Cisco’s OSPF implementation supports these area types: normal/standard areas, backbone area (area 0), transit areas, stub areas, totally stubby areas, NSSA areas, and NSSA totally stubby areas. In a normal OSPF stub area or simply stub area, ABRs exclude external LSAs from being advertised to the area’s routers, which rely on default routing to reach destinations outside the current OSPF autonomous system. This post focuses on normal stub areas and answers the following questions:

  • What is OSPF stub area?
  • What is its purpose?
  • How do OSPF stub areas work?
  • What are the pros and cons of OSPF stub areas?
  • How to configure an OSPF area as a stub area?

Moreover, you will find a lab to set up OSPF stub areas at the end of this tutorial. Note that OSPF stub areas are outside of the CCNA exam’s scope; however, they are part of the CCNP Enterprise ENCOR and ENARSI exams.

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What is OSPF Stub Area, and What is its Purpose?

An OSPF stub area is a special area type that excludes LSAs Type 4 and 5, while it allows only LSAs Type 1, 2, and 3. The purpose of a stub area is to reduce the size of the LSDB; thus, the stub area’s nodes consume fewer CPU cycles than normal area nodes when performing SPF calculations, and decrease convergence time. Remember that the SPF algorithm operates per area; the more the area’s LSA content is smaller, the fastest SPF calculations get done.

Finally, here are some rules that control an OSPF stub area:

  • Routers, including ABRs, cannot inject external routes within the stub area. Therefore, no router can be considered ASBR in the area. However, backbone routers can still redistribute external routes into OSPF and advertise them using LSAs Type 5 into area 0, and normal areas.
  • ABRs cannot flood external AS LSAs into the area.
  • Each ABR advertises a default route using an LSA Type 3 in the area in order to keep external prefixes reachable to the area’s routers. This is a common rule for all the four types of stub areas: normal stub, totally stub, Not-So-Stubby Area (NSSA), and totally Not-So-Stubby Area (NSSA).
  • An OSPF stub area cannot be used as a transit area for virtual links.
  • The backbone area (area 0) cannot become stub.
  • All routers within a stub area should be configured as stub nodes. If an OSPF stub area includes two neighboring routers, one is configured as a stub router while the other does not, they won’t establish a full neighbor relationship in that area.

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How Does an OSPF Stub Area Work?

In this section, I will use the following network topology to explain how OSPF stub areas work.

ospf-stub-area-network-diagram

Figure 1 – Network topology of an OSPF autonomous system

First of all, we configure OSPF and EIGRP according to the network diagram. Each OSPF router has been assigned a router ID written in the N.N.N.N form, where N is the router’s number in Figure 1. Additionally, no virtual link has been established, and we redistributed routes between EIGRP and OSPF on router R2. Here are the configurations applied to the routers.

Router(config)# hostname R1
R1(config)# interface gigabitethernet 0/2
R1(config-if)# ip address 10.0.12.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface gigabitethernet 0/3
R1(config-if)# ip address 10.0.13.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface gigabitethernet 0/4
R1(config-if)# ip address 10.0.14.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface gigabitethernet 0/7
R1(config-if)# ip address 10.0.17.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface gigabitethernet 0/8
R1(config-if)# ip address 10.0.18.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# router ospf 1
R1(config-router)# router-id 1.1.1.1
R1(config-router)# network 10.0.12.1 0.0.0.0 area 0
R1(config-router)# network 10.0.18.1 0.0.0.0 area 0
R1(config-router)# network 10.0.13.1 0.0.0.0 area 13489
R1(config-router)# network 10.0.14.1 0.0.0.0 area 13489
R1(config-router)#
R1(config-router)# router eigrp 100
R1(config-router)# network 10.0.17.1 0.0.0.0
R1(config-router)# no auto-summary

Router(config)# hostname R2
R2(config)# interface gigabitethernet 0/1
R2(config-if)# ip address 10.0.12.2 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)#
R2(config-if)# interface gigabitethernet 0/5
R2(config-if)# ip address 10.0.25.2 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)#
R2(config-if)# interface gigabitethernet 0/6
R2(config-if)# ip address 10.0.26.2 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)#
R2(config-if)# router ospf 1
R2(config-router)# router-id 2.2.2.2
R2(config-router)# network 10.0.12.2 0.0.0.0 area 0
R2(config-router)# network 10.0.25.2 0.0.0.0 area 25
R2(config-router)# redistribute eigrp 200 subnets
R2(config-router)#
R2(config-router)# router eigrp 200
R2(config-router)# network 10.0.26.2 0.0.0.0
R2(config-router)# redistribute ospf 1 metric 1 1 1 1 1
R2(config-router)# no auto-summary

Router(config)# hostname R3
R3(config)# interface gigabitethernet 0/1
R3(config-if)# ip address 10.0.13.3 255.255.255.0
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface gigabitethernet 0/4
R3(config-if)# ip address 10.0.34.3 255.255.255.0
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface gigabitethernet 0/8
R3(config-if)# ip address 10.0.38.3 255.255.255.0
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface gigabitethernet 0/9
R3(config-if)# ip address 10.0.39.3 255.255.255.0
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# router ospf 1
R3(config-router)# router-id 3.3.3.3
R3(config-router)# network 10.0.13.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.34.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.38.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.39.3 0.0.0.0 area 13489

Router(config)# hostname R4
R4(config)# interface gigabitethernet 0/1
R4(config-if)# ip address 10.0.14.4 255.255.255.0
R4(config-if)# no shutdown
R4(config-if)#
R4(config-if)# interface gigabitethernet 0/3
R4(config-if)# ip address 10.0.34.4 255.255.255.0
R4(config-if)# no shutdown
R4(config-if)#
R4(config-if)# interface gigabitethernet 0/7
R4(config-if)# ip address 10.0.47.4 255.255.255.0
R4(config-if)# no shutdown
R4(config-if)#
R4(config-if)# router ospf 1
R4(config-router)# router-id 4.4.4.4
R4(config-router)# network 10.0.14.4 0.0.0.0 area 13489
R4(config-router)# network 10.0.34.4 0.0.0.0 area 13489
R4(config-router)#
R4(config-router)# router eigrp 100
R4(config-router)# network 10.0.47.4 0.0.0.0
R4(config-router)# no auto-summary

Router(config)# hostname R5
R5(config)# interface gigabitethernet 0/2
R5(config-if)# ip address 10.0.25.5 255.255.255.0
R5(config-if)# no shutdown
R5(config-if)#
R5(config-if)# router ospf 1
R5(config-router)# router-id 5.5.5.5
R5(config-router)# network 10.0.25.5 0.0.0.0 area 25

Router(config)# hostname R6
R6(config)# interface gigabitethernet 0/2
R6(config-if)# ip address 10.0.26.6 255.255.255.0
R6(config-if)# no shutdown
R6(config-if)#
R6(config-if)# router eigrp 200
R6(config-router)# network 10.0.26.6 0.0.0.0
R6(config-router)# no auto-summary

Router(config)# hostname R7
R7(config)# interface gigabitethernet 0/1
R7(config-if)# ip address 10.0.17.7 255.255.255.0
R7(config-if)# no shutdown
R7(config-if)#
R7(config-if)# interface gigabitethernet 0/4
R7(config-if)# ip address 10.0.47.7 255.255.255.0
R7(config-if)# no shutdown
R7(config-if)#
R7(config-if)# router eigrp 100
R7(config-router)# network 10.0.17.7 0.0.0.0
R7(config-router)# network 10.0.47.7 0.0.0.0
R7(config-router)# no auto-summary

Router(config)# hostname R8
R8(config)# interface gigabitethernet 0/1
R8(config-if)# ip address 10.0.18.8 255.255.255.0
R8(config-if)# no shutdown
R8(config-if)#
R8(config-if)# interface gigabitethernet 0/3
R8(config-if)# ip address 10.0.38.8 255.255.255.0
R8(config-if)# no shutdown
R8(config-if)#
R8(config-if)# interface gigabitethernet 0/9
R8(config-if)# ip address 10.0.89.8 255.255.255.0
R8(config-if)# no shutdown
R8(config-if)#
R8(config-if)# router ospf 1
R8(config-router)# router-id 8.8.8.8
R8(config-router)# network 10.0.18.8 0.0.0.0 area 0
R8(config-router)# network 10.0.38.8 0.0.0.0 area 13489
R8(config-router)# network 10.0.89.8 0.0.0.0 area 89

Router(config)# hostname R9
R9(config)# interface gigabitethernet 0/3
R9(config-if)# ip address 10.0.39.9 255.255.255.0
R9(config-if)# no shutdown
R9(config-if)#
R9(config-if)# interface gigabitethernet 0/8
R9(config-if)# ip address 10.0.89.9 255.255.255.0
R9(config-if)# no shutdown
R9(config-if)#
R9(config-if)# interface gigabitethernet 0/10
R9(config-if)# ip address 10.0.91.9 255.255.255.0
R9(config-if)# no shutdown
R9(config-if)#
R9(config-if)# router ospf 1
R9(config-router)# router-id 9.9.9.9
R9(config-router)# network 10.0.39.9 0.0.0.0 area 13489
R9(config-router)# network 10.0.89.9 0.0.0.0 area 89
R9(config-router)# network 10.0.91.9 0.0.0.0 area 91

Router(config)# hostname R10
R10(config)# interface gigabitethernet 0/9
R10(config-if)# ip address 10.0.91.10 255.255.255.0
R10(config-if)# no shutdown
R10(config-if)#
R10(config-if)# router ospf 1
R10(config-router)# router-id 10.10.10.10
R10(config-router)# network 10.0.91.10 0.0.0.0 area 91

The OSPF routing domain in Figure 1 includes 5 areas: 0, 25, 89, 91, and 13489. Routers in areas 91 and 13489 need to know every subnet in the OSPF autonomous system but do not require detailed routing information about external destinations. Thus, configuring areas 91 and 13489 as stub areas is enough to meet these requirements. However, that may lead to nonoptimal routing, as we will discover later in this section.

To set up a normal/standard area as a stub area, use the area area-id stub command in router configuration mode (Exhibits 1 to 6), where area-id is the area intended to become a stub. The command must be issued on all routers in the stub area.

Router R1

R1(config)# router ospf 1
R1(config-router)# area 13489 stub

Exhibit 1 – Configuring an OSPF stub area on R1

Router R3

R3(config)# router ospf 1
R3(config-router)# area 13489 stub

Exhibit 2 – Configuring an OSPF stub area on R3

Router R4

R4(config)# router ospf 1
R4(config-router)# area 13489 stub

Exhibit 3 – Configuring an OSPF stub area on R4

Router R8

R8(config)# router ospf 1
R8(config-router)# area 13489 stub

Exhibit 4 – Configuring an OSPF stub area on R8

Router R9

R9(config)# router ospf 1
R9(config-router)# area 13489 stub
R9(config-router)# area 91stub

Exhibit 5 – Configuring two OSPF stub areas on R9

Router R10

R10(config)# router ospf 1
R10(config-router)# area 91 stub

Exhibit 6 – Configuring an OSPF stub area on R10

Before converting area 13489 into a stub, R3’s routing table already included an external OSPF route (Exhibit 7).

Router R3

R3# show ip route ospf


omitted output

Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 14 subnets, 2 masks
O IA     10.0.12.0/24 [110/2] via 10.0.13.1, 00:10:47, GigabitEthernet0/1
O        10.0.14.0/24 [110/2] via 10.0.34.4, 00:10:29, GigabitEthernet0/4
[110/2] via 10.0.13.1, 00:10:47, GigabitEthernet0/1
O IA     10.0.18.0/24 [110/2] via 10.0.38.8, 00:09:21, GigabitEthernet0/8
[110/2] via 10.0.13.1, 00:10:47, GigabitEthernet0/1
O IA     10.0.25.0/24 [110/3] via 10.0.13.1, 00:10:47, GigabitEthernet0/1
O E2     10.0.26.0/24 [110/20] via 10.0.13.1, 00:10:47, GigabitEthernet0/1
O IA     10.0.89.0/24 [110/2] via 10.0.38.8, 00:09:21, GigabitEthernet0/8

Exhibit 7 – OSPF routes installed in R3’s routing table before converting area 13489 into a stub area

Now, router R3 does not have external routes; however, it still can reach subnet 10.0.26.0/24 (advertised in EIGRP AS 200) thanks to the default route advertised by ABRs R1 and R8 (Exhibit 8). Before continuing, remember that we did not inject EIGRP AS 100’s subnets into OSPF yet. Therefore, 10.0.26.0/24 is the only external IP prefix that got advertised in our OSPF autonomous system.

Router R3

R3# show ip route ospf
omitted output

Gateway of last resort is 10.0.38.8 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/2] via 10.0.38.8, 00:21:27, GigabitEthernet0/8
                [110/2] via 10.0.13.1, 00:21:47, GigabitEthernet0/1
      10.0.0.0/8 is variably subnetted, 13 subnets, 2 masks
O IA     10.0.12.0/24 [110/2] via 10.0.13.1, 00:21:57, GigabitEthernet0/1
O        10.0.14.0/24 [110/2] via 10.0.34.4, 00:21:37, GigabitEthernet0/4
                      [110/2] via 10.0.13.1, 00:21:37, GigabitEthernet0/1
O IA     10.0.18.0/24 [110/2] via 10.0.38.8, 00:21:27, GigabitEthernet0/8
                      [110/2] via 10.0.13.1, 00:21:57, GigabitEthernet0/1
O IA     10.0.25.0/24 [110/3] via 10.0.13.1, 00:21:57, GigabitEthernet0/1
O IA     10.0.89.0/24 [110/2] via 10.0.38.8, 00:21:27, GigabitEthernet0/8

Exhibit 8 – OSPF routes installed in R3’s routing table after converting area 13489 into a stub area

The show ip ospf database command outputs below indicate that area 13489’s LS set includes LSAs Type 1, 2, and 3 only (Exhibit 9), while area 89’s LS sets contain LSAs Type 1, 2, 3, and 4 (Exhibit 10). Additionally, area 91’s LSDB consists of Type 1 and Type 2 LSAs (Exhibit 11) because the area does not have an ABR. In fact, routers R9 and R10 are not ABRs .

Router R3

R3# show ip ospf database         

            OSPF Router with ID (3.3.3.3) (Process ID 1)

                Router Link States (Area 13489)

Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         577         0x8000000A 0x009B10 2
3.3.3.3         3.3.3.3         486         0x8000000E 0x003F33 4
4.4.4.4         4.4.4.4         501         0x80000009 0x002C38 2
8.8.8.8         8.8.8.8         652         0x80000007 0x005B22 1
9.9.9.9         9.9.9.9         451         0x80000008 0x003839 1

                Net Link States (Area 13489)

Link ID         ADV Router      Age         Seq#       Checksum
10.0.13.3       3.3.3.3         486         0x80000006 0x00C13F
10.0.14.4       4.4.4.4         501         0x80000002 0x00B842
10.0.34.4       4.4.4.4         501         0x80000006 0x0038A2
10.0.38.8       8.8.8.8         652         0x80000002 0x00FBBA
10.0.39.9       9.9.9.9         451         0x80000002 0x00EAC1

                Summary Net Link States (Area 13489)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         1.1.1.1         577         0x80000002 0x0091A7
0.0.0.0         8.8.8.8         652         0x80000002 0x00BE5E
10.0.12.0       1.1.1.1         577         0x80000005 0x00849B
10.0.12.0       8.8.8.8         652         0x80000005 0x00BB47
10.0.18.0       1.1.1.1         577         0x80000005 0x0042D7
10.0.18.0       8.8.8.8         652         0x80000005 0x006F8E
10.0.25.0       1.1.1.1         577         0x80000005 0x00FE13
10.0.25.0       8.8.8.8         652         0x80000005 0x0036BE
10.0.89.0       1.1.1.1         577         0x80000005 0x003C95
10.0.89.0       8.8.8.8         652         0x80000005 0x005F57

Exhibit 9 – Router R3’s LSDB

Router R8

R8# show ip ospf database 

omitted output


                Router Link States (Area 89)

Link ID         ADV Router      Age         Seq#       Checksum Link count
8.8.8.8         8.8.8.8         1696        0x80000006 0x00AF65 1
9.9.9.9         9.9.9.9         1729        0x80000006 0x006E9E 1

                Net Link States (Area 89)

Link ID         ADV Router      Age         Seq#       Checksum
10.0.89.9       9.9.9.9         1729        0x80000004 0x009BC6

                Summary Net Link States (Area 89)

Link ID         ADV Router      Age         Seq#       Checksum
10.0.12.0       8.8.8.8         1696        0x80000004 0x009F62
10.0.13.0       8.8.8.8         1696        0x80000004 0x00946C
10.0.14.0       8.8.8.8         1696        0x80000004 0x00936B
10.0.18.0       8.8.8.8         1696        0x80000004 0x0053A9
10.0.25.0       8.8.8.8         1696        0x80000004 0x001AD9
10.0.34.0       8.8.8.8         1696        0x80000004 0x00AC3F
10.0.38.0       8.8.8.8         1696        0x80000004 0x007672
10.0.39.0       8.8.8.8         1696        0x80000004 0x007571

                Summary ASB Link States (Area 89)

Link ID         ADV Router      Age         Seq#       Checksum
2.2.2.2         8.8.8.8         1696        0x80000004 0x003CD2



omitted output

Exhibit 10 – Router R8’s LSDB

Router R10

R10# show ip ospf database 

            OSPF Router with ID (10.10.10.10) (Process ID 1)

                Router Link States (Area 91)

Link ID         ADV Router      Age         Seq#       Checksum Link count
9.9.9.9         9.9.9.9         25          0x80000007 0x00C048 1
10.10.10.10     10.10.10.10     24          0x80000006 0x00847C 1

                Net Link States (Area 91)

Link ID         ADV Router      Age         Seq#       Checksum
10.0.91.10      10.10.10.10     24          0x80000001 0x00D582

Exhibit 11 – Router R10’s LSDB

As a general rule, when a router is connected to normal stub areas only, it cannot receive Type 4 and 5 LSAs. However, if it is connected to areas of different types and it is ABR or attached to an area containing an ABR, it may get/generate LSAs Type 4 and 5.

Consequently, R3 and R4’s LSDBs do not include LSAs Type 5, while the LSDBs of routers R1, R2, R5, R8, and R9 do (Exhibit 12). Note that OSPF LSAs Type 5 do not get associated with a particular area, unlike LSAs Type 1, 2, 3, and 4.

Router R9

R9# show ip ospf database 

omitted output


                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
10.0.26.0       2.2.2.2         833         0x80000005 0x00026E 0

Exhibit 12 – Router R9’s LSDB

Another issue with OSPF stub areas is that routers cannot use them as transit areas to build up virtual links. If you try to configure a virtual link using a stub area, Cisco IOS displays the following message.

R9(config-router)# area 13489 virtual-link 8.8.8.8
% OSPF: Virtual links are not allowed in NSSA and stub areas

Router R10 cannot reach IP prefixes outside OSPF area 91 because it is connected to one area, which does not include an ABR. To fix this, we have to connect R9 to area 0. This can be done using a GRE tunnel or OSPF virtual link with R1 or R8. R9 cannot establish a virtual link with R1 because they connected via area 13489 only, which is a stub area.

In contrast, R9 can build up a virtual link with R8 through area 89 (non-stub area) (Exhibits 15 and 16). To do this, use the area virtual-link command on both R9 and R8 (Exhibits 13 and 14). This way, R9 will advertise all internal OSPF prefixes and a default into area 91; thus, R10 can have full IP reachability to all internal and external IP prefixes advertised in the OSPF domain (Exhibit 17).

Router R8

R8(config)# router ospf 1
R8(config-router)# area 89 virtual-link 9.9.9.9

Exhibit 13 – Configuring a virtual link to R9

Router R9

R9(config)# router ospf 1
R9(config-router)# area 89 virtual-link 8.8.8.8

Exhibit 14 – Configuring a virtual link to R8

Exhibits 15 and 16 state that the virtual link between routers R8 and R9 is up and running.

Router R8

R8# show ip ospf interface
OSPF_VL0 is up, line protocol is up
Internet Address 10.0.89.8/24, Area 0, Attached via Not Attached
Process ID 1, Router ID 8.8.8.8, Network Type VIRTUAL_LINK, Cost: 1
Topology-MTID    Cost    Disabled    Shutdown      Topology Name
0           1         no          no            Base
Configured as demand circuit
Run as demand circuit
DoNotAge LSA allowed
Transmit Delay is 1 sec, State POINT_TO_POINT
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:01
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/2/4, flood queue length 0
Next 0x0(0)/0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 1 msec, maximum is 1 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 9.9.9.9  (Hello suppressed)
Suppress hello for 1 neighbor(s)

omitted output

Exhibit 15 – OSPF virtual link interface on R8

Router R9

R9# show ip ospf interface
OSPF_VL0 is up, line protocol is up
Internet Address 10.0.89.9/24, Area 0, Attached via Not Attached
Process ID 1, Router ID 9.9.9.9, Network Type VIRTUAL_LINK, Cost: 1
Topology-MTID    Cost    Disabled    Shutdown      Topology Name
0           1         no          no            Base
Configured as demand circuit
Run as demand circuit
DoNotAge LSA allowed
Transmit Delay is 1 sec, State POINT_TO_POINT
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:07
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/1/4, flood queue length 0
Next 0x0(0)/0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 1 msec, maximum is 1 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 8.8.8.8  (Hello suppressed)
Suppress hello for 1 neighbor(s)


omitted output

Exhibit 16 – OSPF virtual link interface on R9

The show ip route ospf command output in Exhibit 17 states that R10’s routing database includes routes to all internal subnets in the network. It does not have routes to external subnets, but it contains a gateway of last resort that can be used to forward IP packets to destinations that do have a matching entry.

Router R10

R10# show ip route ospf

omitted output

Gateway of last resort is 10.0.91.9 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/2] via 10.0.91.9, 00:17:51, GigabitEthernet0/9
      10.0.0.0/8 is variably subnetted, 11 subnets, 2 masks
O IA     10.0.12.0/24 [110/4] via 10.0.91.9, 00:17:47, GigabitEthernet0/9
O IA     10.0.13.0/24 [110/3] via 10.0.91.9, 00:17:51, GigabitEthernet0/9
O IA     10.0.14.0/24 [110/4] via 10.0.91.9, 00:17:51, GigabitEthernet0/9
O IA     10.0.18.0/24 [110/3] via 10.0.91.9, 00:17:47, GigabitEthernet0/9
O IA     10.0.25.0/24 [110/5] via 10.0.91.9, 00:17:47, GigabitEthernet0/9
O IA     10.0.34.0/24 [110/3] via 10.0.91.9, 00:17:51, GigabitEthernet0/9
O IA     10.0.38.0/24 [110/3] via 10.0.91.9, 00:17:51, GigabitEthernet0/9
O IA     10.0.39.0/24 [110/2] via 10.0.91.9, 00:17:51, GigabitEthernet0/9
O IA     10.0.89.0/24 [110/2] via 10.0.91.9, 00:17:51, GigabitEthernet0/9

Exhibit 17 – OSPF routes installed in R10’s routing table

Routers cannot become ASBRs in a stub area. This means OSPF routers cannot inject external prefixes into a stub area. In other words, they can not share external destinations with OSPF nodes within a stub area. However, if a router, whether it is ABR or not, is connected to multiple areas, including stub and normal areas, the router can still inject external routes into normal areas.

For example, if we instruct router R4 to redistribute EIGRP AS 100’s routes into OSPF, this action won’t succeed, no route will get advertised in area 13489 (the only area to which R4 is attached), and Cisco IOS will display an error message (Exhibit 18).

Router R4

R4(config)# router ospf 1
R4(config-router)# redistribute eigrp 100 subnets
R4(config-router)# 
*Jul 16 00:06:22.571: %OSPF-4-ASBR_WITHOUT_VALID_AREA: Router is currently an ASBR while having only one area which is a stub area

Exhibit 18 – Attempting to redistribute EIGRP 100’s routes on R4

On the other hand, if we try to redistribute those routes into OSPF on router R1, they will get advertised using LSAs Type 5 to OSPF nodes across non-stub areas. In fact, router R1 won’t advertise EIGRP AS 100’s routes to R3 and R4 because it has full neighbor relationships with them in the 13489 stub area only.

In contrast, R8 and R2 will get LSAs Type 5 for those routes from R1 since it is establishing OSPF adjacencies with R2 and R8 in area 0. Additionally, router R2 and R8 will flood those LSAs Type 5 in areas 25 and 89 because they are not stub areas.

Finally, OSPF routers R1, R2, R5, R8, and R9 have detailed routing information about all IP prefixes advertised in the OSPF routing domain, as you can see in the show ip route command output below.

R1# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 18 subnets, 2 masks
C 10.0.12.0/24 is directly connected, GigabitEthernet0/2
L 10.0.12.1/32 is directly connected, GigabitEthernet0/2
C 10.0.13.0/24 is directly connected, GigabitEthernet0/3
L 10.0.13.1/32 is directly connected, GigabitEthernet0/3
C 10.0.14.0/24 is directly connected, GigabitEthernet0/4
L 10.0.14.1/32 is directly connected, GigabitEthernet0/4
C 10.0.17.0/24 is directly connected, GigabitEthernet0/7
L 10.0.17.1/32 is directly connected, GigabitEthernet0/7
C 10.0.18.0/24 is directly connected, GigabitEthernet0/8
L 10.0.18.1/32 is directly connected, GigabitEthernet0/8
O IA 10.0.25.0/24 [110/2] via 10.0.12.2, 00:05:51, GigabitEthernet0/2
O E2 10.0.26.0/24 [110/20] via 10.0.12.2, 00:05:51, GigabitEthernet0/2
O 10.0.34.0/24 [110/2] via 10.0.14.4, 02:47:12, GigabitEthernet0/4
               [110/2] via 10.0.13.3, 02:47:12, GigabitEthernet0/3
O 10.0.38.0/24 [110/2] via 10.0.13.3, 02:47:12, GigabitEthernet0/3
O 10.0.39.0/24 [110/2] via 10.0.13.3, 02:47:01, GigabitEthernet0/3
D 10.0.47.0/24 [90/3072] via 10.0.17.7, 04:06:06, GigabitEthernet0/7
O IA 10.0.89.0/24 [110/2] via 10.0.18.8, 02:47:43, GigabitEthernet0/8
O IA 10.0.91.0/24 [110/3] via 10.0.18.8, 00:53:11, GigabitEthernet0/8
R2# show ip route 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 16 subnets, 2 masks
C 10.0.12.0/24 is directly connected, GigabitEthernet0/1
L 10.0.12.2/32 is directly connected, GigabitEthernet0/1
O IA 10.0.13.0/24 [110/2] via 10.0.12.1, 00:06:30, GigabitEthernet0/1
O IA 10.0.14.0/24 [110/2] via 10.0.12.1, 00:06:30, GigabitEthernet0/1
O E2 10.0.17.0/24 [110/20] via 10.0.12.1, 00:02:51, GigabitEthernet0/1
O 10.0.18.0/24 [110/2] via 10.0.12.1, 00:06:30, GigabitEthernet0/1
C 10.0.25.0/24 is directly connected, GigabitEthernet0/5
L 10.0.25.2/32 is directly connected, GigabitEthernet0/5
C 10.0.26.0/24 is directly connected, GigabitEthernet0/6
L 10.0.26.2/32 is directly connected, GigabitEthernet0/6
O IA 10.0.34.0/24 [110/3] via 10.0.12.1, 00:06:30, GigabitEthernet0/1
O IA 10.0.38.0/24 [110/3] via 10.0.12.1, 00:06:30, GigabitEthernet0/1
O IA 10.0.39.0/24 [110/3] via 10.0.12.1, 00:06:30, GigabitEthernet0/1
O E2 10.0.47.0/24 [110/20] via 10.0.12.1, 00:02:51, GigabitEthernet0/1
O IA 10.0.89.0/24 [110/3] via 10.0.12.1, 00:06:30, GigabitEthernet0/1
O IA 10.0.91.0/24 [110/4] via 10.0.12.1, 00:06:30, GigabitEthernet0/1
R5# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 14 subnets, 2 masks
O IA 10.0.12.0/24 [110/2] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
O IA 10.0.13.0/24 [110/3] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
O IA 10.0.14.0/24 [110/3] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
O E2 10.0.17.0/24 [110/20] via 10.0.25.2, 00:04:05, GigabitEthernet0/2
O IA 10.0.18.0/24 [110/3] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
C 10.0.25.0/24 is directly connected, GigabitEthernet0/2
L 10.0.25.5/32 is directly connected, GigabitEthernet0/2
O E2 10.0.26.0/24 [110/20] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
O IA 10.0.34.0/24 [110/4] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
O IA 10.0.38.0/24 [110/4] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
O IA 10.0.39.0/24 [110/4] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
O E2 10.0.47.0/24 [110/20] via 10.0.25.2, 00:04:05, GigabitEthernet0/2
O IA 10.0.89.0/24 [110/4] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
O IA 10.0.91.0/24 [110/5] via 10.0.25.2, 00:07:44, GigabitEthernet0/2
R8# show ip route 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 16 subnets, 2 masks
O 10.0.12.0/24 [110/2] via 10.0.18.1, 00:08:45, GigabitEthernet0/1
O 10.0.13.0/24 [110/2] via 10.0.38.3, 02:50:13, GigabitEthernet0/3
O 10.0.14.0/24 [110/3] via 10.0.38.3, 02:50:03, GigabitEthernet0/3
O E2 10.0.17.0/24 [110/20] via 10.0.18.1, 00:05:01, GigabitEthernet0/1
C 10.0.18.0/24 is directly connected, GigabitEthernet0/1
L 10.0.18.8/32 is directly connected, GigabitEthernet0/1
O IA 10.0.25.0/24 [110/3] via 10.0.18.1, 00:08:35, GigabitEthernet0/1
O E2 10.0.26.0/24 [110/20] via 10.0.18.1, 00:08:35, GigabitEthernet0/1
O 10.0.34.0/24 [110/2] via 10.0.38.3, 02:50:13, GigabitEthernet0/3
C 10.0.38.0/24 is directly connected, GigabitEthernet0/3
L 10.0.38.8/32 is directly connected, GigabitEthernet0/3
O 10.0.39.0/24 [110/2] via 10.0.38.3, 02:50:03, GigabitEthernet0/3
O E2 10.0.47.0/24 [110/20] via 10.0.18.1, 00:05:01, GigabitEthernet0/1
C 10.0.89.0/24 is directly connected, GigabitEthernet0/9
L 10.0.89.8/32 is directly connected, GigabitEthernet0/9
O IA 10.0.91.0/24 [110/2] via 10.0.89.9, 00:55:59, GigabitEthernet0/9
R9# show ip route 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 16 subnets, 2 masks
O 10.0.12.0/24 [110/3] via 10.0.89.8, 00:09:27, GigabitEthernet0/8
O 10.0.13.0/24 [110/2] via 10.0.39.3, 00:56:56, GigabitEthernet0/3
O 10.0.14.0/24 [110/3] via 10.0.39.3, 00:56:56, GigabitEthernet0/3
O E2 10.0.17.0/24 [110/20] via 10.0.89.8, 00:05:43, GigabitEthernet0/8
O 10.0.18.0/24 [110/2] via 10.0.89.8, 00:56:46, GigabitEthernet0/8
O IA 10.0.25.0/24 [110/4] via 10.0.89.8, 00:09:17, GigabitEthernet0/8
O E2 10.0.26.0/24 [110/20] via 10.0.89.8, 00:09:17, GigabitEthernet0/8
O 10.0.34.0/24 [110/2] via 10.0.39.3, 00:56:56, GigabitEthernet0/3
O 10.0.38.0/24 [110/2] via 10.0.39.3, 00:56:56, GigabitEthernet0/3
C 10.0.39.0/24 is directly connected, GigabitEthernet0/3
L 10.0.39.9/32 is directly connected, GigabitEthernet0/3
O E2 10.0.47.0/24 [110/20] via 10.0.89.8, 00:05:43, GigabitEthernet0/8
C 10.0.89.0/24 is directly connected, GigabitEthernet0/8
L 10.0.89.9/32 is directly connected, GigabitEthernet0/8
C 10.0.91.0/24 is directly connected, GigabitEthernet0/10
L 10.0.91.9/32 is directly connected, GigabitEthernet0/10

Similar to R3 and R4, R10 has detailed routing data about internal destinations in the OSPF autonomous system and uses a default route generated by router R9 to reach external IP prefixes, as shown in the following show ip route command outputs.

R3# show ip route 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is 10.0.39.9 to network 0.0.0.0

O*IA 0.0.0.0/0 [110/2] via 10.0.39.9, 00:54:50, GigabitEthernet0/9
               [110/2] via 10.0.38.8, 02:48:39, GigabitEthernet0/8
               [110/2] via 10.0.13.1, 02:48:59, GigabitEthernet0/1
10.0.0.0/8 is variably subnetted, 14 subnets, 2 masks
O IA 10.0.12.0/24 [110/2] via 10.0.13.1, 02:49:09, GigabitEthernet0/1
C 10.0.13.0/24 is directly connected, GigabitEthernet0/1
L 10.0.13.3/32 is directly connected, GigabitEthernet0/1
O 10.0.14.0/24 [110/2] via 10.0.34.4, 02:48:49, GigabitEthernet0/4
               [110/2] via 10.0.13.1, 02:48:49, GigabitEthernet0/1
O IA 10.0.18.0/24 [110/2] via 10.0.38.8, 02:48:39, GigabitEthernet0/8
                  [110/2] via 10.0.13.1, 02:49:09, GigabitEthernet0/1
O IA 10.0.25.0/24 [110/3] via 10.0.13.1, 00:07:17, GigabitEthernet0/1
C 10.0.34.0/24 is directly connected, GigabitEthernet0/4
L 10.0.34.3/32 is directly connected, GigabitEthernet0/4
C 10.0.38.0/24 is directly connected, GigabitEthernet0/8
L 10.0.38.3/32 is directly connected, GigabitEthernet0/8
C 10.0.39.0/24 is directly connected, GigabitEthernet0/9
L 10.0.39.3/32 is directly connected, GigabitEthernet0/9
O IA 10.0.89.0/24 [110/2] via 10.0.39.9, 00:54:50, GigabitEthernet0/9
                  [110/2] via 10.0.38.8, 02:48:39, GigabitEthernet0/8
O IA 10.0.91.0/24 [110/2] via 10.0.39.9, 00:54:50, GigabitEthernet0/9
R4# show ip route 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is 10.0.14.1 to network 0.0.0.0

O*IA 0.0.0.0/0 [110/2] via 10.0.14.1, 02:49:04, GigabitEthernet0/1
10.0.0.0/8 is variably subnetted, 15 subnets, 2 masks
O IA 10.0.12.0/24 [110/2] via 10.0.14.1, 02:49:14, GigabitEthernet0/1
O 10.0.13.0/24 [110/2] via 10.0.34.3, 02:49:14, GigabitEthernet0/3
               [110/2] via 10.0.14.1, 02:49:14, GigabitEthernet0/1
C 10.0.14.0/24 is directly connected, GigabitEthernet0/1
L 10.0.14.4/32 is directly connected, GigabitEthernet0/1
D 10.0.17.0/24 [90/3072] via 10.0.47.7, 04:08:00, GigabitEthernet0/7
O IA 10.0.18.0/24 [110/2] via 10.0.14.1, 02:49:14, GigabitEthernet0/1
O IA 10.0.25.0/24 [110/3] via 10.0.14.1, 00:07:29, GigabitEthernet0/1
C 10.0.34.0/24 is directly connected, GigabitEthernet0/3
L 10.0.34.4/32 is directly connected, GigabitEthernet0/3
O 10.0.38.0/24 [110/2] via 10.0.34.3, 02:48:54, GigabitEthernet0/3
O 10.0.39.0/24 [110/2] via 10.0.34.3, 02:48:54, GigabitEthernet0/3
C 10.0.47.0/24 is directly connected, GigabitEthernet0/7
L 10.0.47.4/32 is directly connected, GigabitEthernet0/7
O IA 10.0.89.0/24 [110/3] via 10.0.34.3, 00:55:02, GigabitEthernet0/3
                  [110/3] via 10.0.14.1, 02:49:14, GigabitEthernet0/1
O IA 10.0.91.0/24 [110/3] via 10.0.34.3, 00:55:02, GigabitEthernet0/3
R10# show ip route 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is 10.0.91.9 to network 0.0.0.0

O*IA 0.0.0.0/0 [110/2] via 10.0.91.9, 01:01:53, GigabitEthernet0/9
10.0.0.0/8 is variably subnetted, 11 subnets, 2 masks
O IA 10.0.12.0/24 [110/4] via 10.0.91.9, 01:01:49, GigabitEthernet0/9
O IA 10.0.13.0/24 [110/3] via 10.0.91.9, 01:01:53, GigabitEthernet0/9
O IA 10.0.14.0/24 [110/4] via 10.0.91.9, 01:01:53, GigabitEthernet0/9
O IA 10.0.18.0/24 [110/3] via 10.0.91.9, 01:01:49, GigabitEthernet0/9
O IA 10.0.25.0/24 [110/5] via 10.0.91.9, 00:14:17, GigabitEthernet0/9
O IA 10.0.34.0/24 [110/3] via 10.0.91.9, 01:01:53, GigabitEthernet0/9
O IA 10.0.38.0/24 [110/3] via 10.0.91.9, 01:01:53, GigabitEthernet0/9
O IA 10.0.39.0/24 [110/2] via 10.0.91.9, 01:01:53, GigabitEthernet0/9
O IA 10.0.89.0/24 [110/2] via 10.0.91.9, 01:01:53, GigabitEthernet0/9
C 10.0.91.0/24 is directly connected, GigabitEthernet0/9
L 10.0.91.10/32 is directly connected, GigabitEthernet0/9

Three default routes have been installed in R3’s routing table (Exhibit 19). After configuring a virtual link between R9 and R8, R9 becomes ABR; and since it is in the 13489 stub area, it injects a default route in that area. The default routes have the same metric. Therefore, OSPF will load-balance traffic destined to external networks across routers R1, R8, and R9 even though those routes are not equal since routers R8 and R9’s paths to external destinations traverse R1.

Router R3

R3# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is 10.0.39.9 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/2] via 10.0.39.9, 01:13:56, GigabitEthernet0/9
                [110/2] via 10.0.38.8, 03:07:45, GigabitEthernet0/8
                [110/2] via 10.0.13.1, 03:08:05, GigabitEthernet0/1



omitted output

Exhibit 19 – Displaying R3’s routing table

To verify this analysis, you can start monitoring R1, R8, and R9’s interfaces connected to R3 with Wireshark, and then ping all external IPs on the network, which are 10.0.17.1, 10.0.17.7, 10.0.26.2, 10.0.26.6, 10.0.47.4, and 10.0.47.7.

Exhibit 20 shows that ICMP echo requests destined to 10.0.17.7 got forwarded to R1.

Exhibit 20 – Traffic capture on subnet 10.0.13.0/24.

Exhibit 21 shows that ICMP echo request packets destined to 10.0.17.1 got forwarded to R8.

Exhibit 21 – Traffic capture on subnet 10.0.38.0/24.

Exhibit 22 shows that ICMP echo request packets destined to 10.0.26.2, 10.0.26.6, 10.0.47.4, and 10.0.47.7 got forwarded to R9.

Exhibit 22 – Traffic capture on subnet 10.0.39.0/24.

To sum up, OSPF stub areas help reduces the size of the LSDB but may lead to suboptimal routing.

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OSPF Stub Area vs Not-So-Stubby Area (NSSA)

Both stub and NSSA areas do not support external AS LSAs, rely on default routes advertised by ABRs to reach IP prefixes outside the OSPF routing domain, and accept LSAs Type 1, 2, and 3. However, NSSA areas allow configuring ASBRs within the area and flooding external routes into it using LSAs Type 7 instead of Type 5.

OSPF Stub Area vs NSSA Totally Stub Area

Both stub and NSSA Totally Stub areas do not support external AS LSAs, rely on default routes advertised by ABRs to reach IP prefixes outside the OSPF routing domain, and accept LSAs Type 1, 2. However, NSSA totally stub areas allow configuring ASBRs within the area and flooding external routes into it using LSAs Type 7 instead of Type 5, while it prohibits LSAs Type 3 except default summary LSAs, unlike an OSPF stub area.

OSPF Stub Area Flag and Neighbor Relationships

OSPF nodes in a stub area set the stub area flag, the (E) bit in the options field, to 0 in OSPF Hellos sent within the area, as illustrated in the following OSPF hello packet sample.

Open Shortest Path First
    OSPF Header
        Version: 2
        Message Type: Hello Packet (1)
        Packet Length: 48
        Source OSPF Router: 3.3.3.3
        Area ID: 0.0.52.177
        Checksum: 0x3fc5 [correct]
        Auth Type: Null (0)
        Auth Data (none): 0000000000000000
    OSPF Hello Packet
        Network Mask: 255.255.255.0
        Hello Interval [sec]: 10
        Options: 0x10, (L) LLS Data block
            0... .... = DN: Not set
            .0.. .... = O: Not set
            ..0. .... = (DC) Demand Circuits: Not supported
            ...1 .... = (L) LLS Data block: Present
            .... 0... = (N) NSSA: Not supported
            .... .0.. = (MC) Multicast: Not capable
            .... ..0. = (E) External Routing: Not capable
            .... ...0 = (MT) Multi-Topology Routing: No
        Router Priority: 1
        Router Dead Interval [sec]: 40
        Designated Router: 10.0.39.9
        Backup Designated Router: 10.0.39.3
        Active Neighbor: 9.9.9.9

If two OSPF stub area neighbors do not agree on the stub area flag, they cannot build up an OSPF neighbor relationship. On the other hand, within a normal OSPF area, routers set the E to 1, as shown in the following OSPF Hello packet example. This means external routes are allowed and the area is not a stub of any kind.

OSPF Hello Packet
        Network Mask: 255.255.255.0
        Hello Interval [sec]: 10
        Options: 0x12, (L) LLS Data block, (E) External Routing
            0... .... = DN: Not set
            .0.. .... = O: Not set
            ..0. .... = (DC) Demand Circuits: Not supported
            ...1 .... = (L) LLS Data block: Present
            .... 0... = (N) NSSA: Not supported
            .... .0.. = (MC) Multicast: Not capable
            .... ..1. = (E) External Routing: Capable
            .... ...0 = (MT) Multi-Topology Routing: No
        Router Priority: 1
        Router Dead Interval [sec]: 40
        Designated Router: 10.0.100.10
        Backup Designated Router: 10.0.100.9
        Active Neighbor: 9.9.9.9

OSPF LSA Types Allowed within OSPF Stub Areas

An OSPF stub area, regardless of its type, has one goal: to reduce the size of the LSDB in order to calculate the SPF tree fast as possible; besides, stub area nodes rely on default routes, advertised as inter-area OSPF routes by ABRs, to forward IP packets to external destinations. However, stub areas do not allow the same OSPF LSA types, as illustrated in the following table.

Stub Area Type LSA Types External Routes ASBR
LSA Type 1 LSA Type 2 LSA Type 3 LSA Type 4 LSA Type 5 LSA Type 7
Stub yes yes yes No No No No No
Totally stub yes yes No, except for default routes No No No No No
NSSA yes yes yes No No Yes Yes Yes
Totally NSSA yes yes No, except for default routes No No Yes Yes Yes

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Configuring and Verifying an OSPF Stub Area

Stub Area OSPF Configuration and Verification on Cisco IOS

Routers within a stub area should all declare the area as a stub. On Cisco IOS, use the area stub command to achieve this, as shown in the following example.

R1(config)# router ospf 1
R1(config-router)# area 10 stub

To configure an OSPF area as a totally stubby area, use the area stub no-summary command in router configuration mode.

Finally, the show ip ospf command allows you to verify whether an area gets converted to a stub area, as you can see in the following example.

R15# show ip ospf



omitted output


 Cisco NSF helper support enabled
    Area 3
        Number of interfaces in this area is 2 (1 loopback)
        It is a stub area
        Area has no authentication
        SPF algorithm last executed 00:00:04.540 ago
        SPF algorithm executed 2 times
        Area ranges are
        Number of LSA 1. Checksum Sum 0x0046C2
        Number of opaque link LSA 0. Checksum Sum 0x000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0

Stub Area OSPF Configuration on Cisco IOS-XR

On Cisco IOS-XR, use the stub command in area configuration mode in order to set up a specific area as a stub (Exhibit 23).

RP/0/0/CPU0:ios(config)# router ospf 1
RP/0/0/CPU0:ios(config-ospf)# area 20
RP/0/0/CPU0:ios(config-ospf-ar)# stub
RP/0/0/CPU0:ios(config-ospf-ar)# commit

Exhibit 23 – Configuring stub area on Cisco IOS-XR

To verify your configuration, use the show ospf command as shown in the example below.

RP/0/0/CPU0:ios# show ospf



omitted output


 Strict-SPF capability is enabled
    Area 20
        Number of interfaces in this area is 1
        It is a stub area
        SPF algorithm executed 2 times
        Number of LSA 1.  Checksum Sum 0x00a172
        Number of opaque link LSA 0.  Checksum Sum 00000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0
        Number of LFA enabled interfaces 0, LFA revision 0
        Number of Per Prefix LFA enabled interfaces 0
        Number of neighbors forming in staggered mode 0, 0 ful

Stub Area OSPF Configuration on Juniper

Juniper JunOS supports OSPF stub areas. First, use the set protocols ospf area stub command on all routers in the area to configure an area as a stub (Exhibit 24); then issue the set protocols ospf area stub default-metric command on the ABRs intended to inject default routes into the stub area (Exhibit 25).

mohamed@itsb# set protocols ospf area 0.0.0.2 stub
mohamed@itsb# commit

Exhibit 24 – Configuring stub area on Juniper JunOS

mohamed@itsb# set protocols ospf area 0.0.0.2 stub default-metric 20
mohamed@itsb# commit

Exhibit 25 – Injecting a default route into a stub area on Juniper JunOS

To check whether an area is a stub, use the show protocols ospf command. When you issue the command on a non-ABR router, it will display an output similar to Exhibit 26, telling if the area is a stub area. However, when you use the command on an ABR (Exhibit 27), it will display additional information, such as a default route has been injected, the area is totally stubby, etc.

mohamed@itsb#  show protocols ospf
area 0.0.0.2 {
     stub;
}

Exhibit 26 – Verifying a stub area on a non-ABR Juniper router

mohamed@itsb#  show protocols ospf
area 0.0.0.2 {
        stub default-metric 20;
}

Exhibit 27 – Verifying a stub area on an ABR Juniper router

Finally, to configure an OSPF area as a totally stubby area on JunOS, use the set protocols ospf area stub no-summaries command on the area’s ABRs.

Stub Area OSPF Configuration on Mikrotik RouterOS

The /routing ospf area add name area-id type inject-summary-lsa command allows you to set up stub areas on Mikrotik RouterOS. You have to specify the area name, ID, and type, and tell the router to inject summary LSAs (Exhibit 28). Moreover, if you want to set up a totally stubby area, set the inject-summary parameter to no.

[admin@MikroTik] >   /routing ospf area add name=area2 area-id=2.2.2.2 type=stub inject-summary-lsa=yes

Exhibit 28 – Configuring stub area on Mikrotik

To verify your stub area configuration, use the routing ospf area print command (Exhibit 29).

[admin@MikroTik] >  routing ospf area print
Flags: X - disabled, I - invalid, * - default
#    NAME                                 AREA-ID         TYPE    DEFAULT-COST
0  * backbone                             0.0.0.0         default
1    area1                                1.1.1.1         stub               1
2    area2                                2.2.2.2         stub               1

Exhibit 29 – Verifying OSPF stub areas on Mikrotik RouterOS

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OSPF Stub Area Lab

In this lab, you learn commands and develop skills concerning the following topics:

  • OSPF
  • OSPF stub area
  • OSPF virtual links
  • Route redistribution
  • Adjusting OSPF metric
  • EIGRP

Network diagram

ospf-stub-area-network-diagram

IP Addressing and Routing Settings

Router Interface IP Address Autonomous System
or
OSPF Area
R1 GigabitEthernet 0/2 10.0.12.1/24 Area 0
GigabitEthernet 0/3 10.0.13.1/24 Area 13489
GigabitEthernet 0/4 10.0.14.1/24 Area 13489
GigabitEthernet 0/7 10.0.17.1/24 EIGRP 100
GigabitEthernet 0/8 10.0.18.1/24 Area 0
Loopback0 10.0.110.1/32 Area 1
Loopback1 10.0.111.1/32 Area 1
Loopback2 10.0.112.1/32 Area 1
R2 GigabitEthernet 0/1 10.0.12.2/24 Area 0
GigabitEthernet 0/5 10.0.25.2/24 Area 25
GigabitEthernet 0/6 10.0.26.2/24 EIGRP 200
Loopback0 10.0.120.2/32 Area 2
Loopback1 10.0.121.2/32 Area 2
Loopback2 10.0.122.2/32 Area 2
R3 GigabitEthernet 0/1 10.0.13.3/24 Area 13489
GigabitEthernet 0/4 10.0.34.3/24 Area 13489
GigabitEthernet 0/8 10.0.38.3/24 Area 13489
GigabitEthernet 0/9 10.0.39.3/24 Area 13489
Loopback0 10.0.130.3/32 Area 13489
Loopback1 10.0.131.3/32 Area 13489
Loopback2 10.0.132.3/32 Area 13489
R4 GigabitEthernet 0/1 10.0.14.4/24 Area 13489
GigabitEthernet 0/3 10.0.34.4/24 Area 13489
GigabitEthernet 0/7 10.0.47.4/24 EIGRP 100
Loopback0 10.0.140.4/32 EIGRP 100
Loopback1 10.0.141.4/32 EIGRP 100
Loopback2 10.0.142.4/32 Area 13489
R5 GigabitEthernet 0/2 10.0.25.5/24 Area 25
Loopback0 10.0.150.5/32 Area 25
Loopback1 10.0.151.5/32 Area 25
Loopback2 10.0.152.5/32 Area 25
R6 GigabitEthernet 0/2 10.0.26.6/24 EIGRP 200
Loopback0 10.0.160.6/32 EIGRP 200
Loopback1 10.0.161.6/32 EIGRP 200
Loopback2 10.0.162.6/32 EIGRP 200
R7 GigabitEthernet 0/1 10.0.17.7/24 EIGRP 100
GigabitEthernet 0/4 10.0.47.7/24 EIGRP 100
Loopback0 10.0.170.7/32 EIGRP 100
Loopback1 10.0.171.7/32 EIGRP 100
Loopback2 10.0.172.7/32 EIGRP 100
R8 GigabitEthernet 0/1 10.0.18.8/24 Area 0
GigabitEthernet 0/3 10.0.38.8/24 Area 13489
GigabitEthernet 0/9 10.0.89.8/24 Area 89
Loopback0 10.0.180.8/32 Area 8
Loopback1 10.0.181.8/32 Area 8
Loopback2 10.0.182.8/32 Area 8
R9 GigabitEthernet 0/3 10.0.39.9/24 Area 13489
GigabitEthernet 0/8 10.0.89.9/24 Area 89
GigabitEthernet 0/10 10.0.100.9/24 Area 91
Loopback0 10.0.190.9/32 Area 89
Loopback1 10.0.191.9/32 Area 89
Loopback2 10.0.192.9/32 Area 89
R10 GigabitEthernet 0/9 10.0.100.10/24 Area 91
Loopback0 10.0.200.10/32 Area 91
Loopback1 10.0.201.10/32 Area 91
Loopback2 10.0.202.10/32 Area 91

Tasks

Task 1: Configure hostnames and IP addresses according to the table above.

Router(config)# hostname R1
R1(config)#
R1(config)# interface GigabitEthernet0/2
R1(config-if)# ip address 10.0.12.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface GigabitEthernet0/3
R1(config-if)# ip address 10.0.13.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface GigabitEthernet0/4
R1(config-if)# ip address 10.0.14.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface GigabitEthernet0/7
R1(config-if)# ip address 10.0.17.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface GigabitEthernet0/8
R1(config-if)# ip address 10.0.18.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface Loopback0
R1(config-if)# ip address 10.0.110.1 255.255.255.255
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface Loopback1
R1(config-if)# ip address 10.0.111.1 255.255.255.255
R1(config-if)# no shutdown
R1(config-if)#
R1(config-if)# interface Loopback2
R1(config-if)# ip address 10.0.112.1 255.255.255.255
R1(config-if)# no shutdown

Router(config)# hostname R2
R2(config)#
R2(config)# interface GigabitEthernet0/1
R2(config-if)# ip address 10.0.12.2 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)#
R2(config-if)# interface GigabitEthernet0/5
R2(config-if)# ip address 10.0.25.2 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)#
R2(config-if)# interface GigabitEthernet0/6
R2(config-if)# ip address 10.0.26.2 255.255.255.0
R2(config-if)# no shutdown
R2(config-if)#
R2(config-if)# interface Loopback0
R2(config-if)# ip address 10.0.120.2 255.255.255.255
R2(config-if)# no shutdown
R2(config-if)#
R2(config-if)# interface Loopback1
R2(config-if)# ip address 10.0.121.2 255.255.255.255
R2(config-if)# no shutdown
R2(config-if)#
R2(config-if)# interface Loopback2
R2(config-if)# ip address 10.0.122.2 255.255.255.255
R2(config-if)# no shutdown

Router(config)# hostname R3
R3(config)#
R3(config)# interface GigabitEthernet0/1
R3(config-if)# ip address 10.0.13.3 255.255.255.0
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface GigabitEthernet0/4
R3(config-if)# ip address 10.0.34.3 255.255.255.0
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface GigabitEthernet0/8
R3(config-if)# ip address 10.0.38.3 255.255.255.0
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface GigabitEthernet0/9
R3(config-if)# ip address 10.0.39.3 255.255.255.0
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface Loopback0
R3(config-if)# ip address 10.0.130.3 255.255.255.255
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface Loopback1
R3(config-if)# ip address 10.0.131.3 255.255.255.255
R3(config-if)# no shutdown
R3(config-if)#
R3(config-if)# interface Loopback2
R3(config-if)# ip address 10.0.132.3 255.255.255.255
R3(config-if)# no shutdown

Router(config)# hostname R4
R4(config)#
R4(config)# interface GigabitEthernet0/1
R4(config-if)# ip address 10.0.14.4 255.255.255.0
R4(config-if)# no shutdown
R4(config-if)#
R4(config-if)# interface GigabitEthernet0/3
R4(config-if)# ip address 10.0.34.4 255.255.255.0
R4(config-if)# no shutdown
R4(config-if)#
R4(config-if)# interface GigabitEthernet0/7
R4(config-if)# ip address 10.0.47.4 255.255.255.0
R4(config-if)# no shutdown
R4(config-if)#
R4(config-if)# interface Loopback0
R4(config-if)# ip address 10.0.140.4 255.255.255.255
R4(config-if)# no shutdown
R4(config-if)#
R4(config-if)# interface Loopback1
R4(config-if)# ip address 10.0.141.4 255.255.255.255
R4(config-if)# no shutdown
R4(config-if)#
R4(config-if)# interface Loopback2
R4(config-if)# ip address 10.0.142.4 255.255.255.255
R4(config-if)# no shutdown

Router(config)# hostname R5
R5(config)#
R5(config)# interface GigabitEthernet0/2
R5(config-if)# ip address 10.0.25.5 255.255.255.0
R5(config-if)# no shutdown
R5(config-if)#
R5(config-if)# interface Loopback0
R5(config-if)# ip address 10.0.150.5 255.255.255.255
R5(config-if)# no shutdown
R5(config-if)#
R5(config-if)# interface Loopback1
R5(config-if)# ip address 10.0.151.5 255.255.255.255
R5(config-if)# no shutdown
R5(config-if)#
R5(config-if)# interface Loopback2
R5(config-if)# ip address 10.0.152.5 255.255.255.255
R5(config-if)# no shutdown

Router(config)# hostname R6
R6(config)#
R6(config)# interface GigabitEthernet0/2
R6(config-if)# ip address 10.0.26.6 255.255.255.0
R6(config-if)# no shutdown
R6(config-if)#
R6(config-if)# interface Loopback0
R6(config-if)# ip address 10.0.160.6 255.255.255.255
R6(config-if)# no shutdown
R6(config-if)#
R6(config-if)# interface Loopback1
R6(config-if)# ip address 10.0.161.6 255.255.255.255
R6(config-if)# no shutdown
R6(config-if)#
R6(config-if)# interface Loopback2
R6(config-if)# ip address 10.0.162.6 255.255.255.255
R6(config-if)# no shutdown

Router(config)# hostname R7
R7(config)#
R7(config)# interface GigabitEthernet0/1
R7(config-if)# ip address 10.0.17.7 255.255.255.0
R7(config-if)# no shutdown
R7(config-if)#
R7(config-if)# interface GigabitEthernet0/4
R7(config-if)# ip address 10.0.47.7 255.255.255.0
R7(config-if)# no shutdown
R7(config-if)#
R7(config-if)# interface Loopback0
R7(config-if)# ip address 10.0.170.7 255.255.255.255
R7(config-if)# no shutdown
R7(config-if)#
R7(config-if)# interface Loopback1
R7(config-if)# ip address 10.0.171.7 255.255.255.255
R7(config-if)# no shutdown
R7(config-if)#
R7(config-if)# interface Loopback2
R7(config-if)# ip address 10.0.172.7 255.255.255.255
R7(config-if)# no shutdown

Router(config)# hostname R8
R8(config)#
R8(config)# interface GigabitEthernet0/1
R8(config-if)# ip address 10.0.18.8 255.255.255.0
R8(config-if)# no shutdown
R8(config-if)#
R8(config-if)# interface GigabitEthernet0/3
R8(config-if)# ip address 10.0.38.8 255.255.255.0
R8(config-if)# no shutdown
R8(config-if)#
R8(config-if)# interface GigabitEthernet0/9
R8(config-if)# ip address 10.0.89.8 255.255.255.0
R8(config-if)# no shutdown
R8(config-if)#
R8(config-if)# interface Loopback0
R8(config-if)# ip address 10.0.180.8 255.255.255.255
R8(config-if)# no shutdown
R8(config-if)#
R8(config-if)# interface Loopback1
R8(config-if)# ip address 10.0.181.8 255.255.255.255
R8(config-if)# no shutdown
R8(config-if)#
R8(config-if)# interface Loopback2
R8(config-if)# ip address 10.0.182.8 255.255.255.255
R8(config-if)# no shutdown

Router(config)# hostname R9
R9(config)#
R9(config)# interface GigabitEthernet0/3
R9(config-if)# ip address 10.0.39.9 255.255.255.0
R9(config-if)# no shutdown
R9(config-if)#
R9(config-if)# interface GigabitEthernet0/8
R9(config-if)# ip address 10.0.89.9 255.255.255.0
R9(config-if)# no shutdown
R9(config-if)#
R9(config-if)# interface GigabitEthernet0/10
R9(config-if)# ip address 10.0.100.9 255.255.255.0
R9(config-if)# no shutdown
R9(config-if)#
R9(config-if)# interface Loopback0
R9(config-if)# ip address 10.0.190.9 255.255.255.255
R9(config-if)# no shutdown
R9(config-if)#
R9(config-if)# interface Loopback1
R9(config-if)# ip address 10.0.191.9 255.255.255.255
R9(config-if)# no shutdown
R9(config-if)#
R9(config-if)# interface Loopback2
R9(config-if)# ip address 10.0.192.9 255.255.255.255
R9(config-if)# no shutdown

Router(config)# hostname R10
R10(config)#
R10(config)# interface GigabitEthernet0/9
R10(config-if)# ip address 10.0.100.10 255.255.255.0
R10(config-if)# no shutdown
R10(config-if)#
R10(config-if)# interface Loopback0
R10(config-if)# ip address 10.0.200.10 255.255.255.255
R10(config-if)# no shutdown
R10(config-if)#
R10(config-if)# interface Loopback1
R10(config-if)# ip address 10.0.201.10 255.255.255.255
R10(config-if)# no shutdown
R10(config-if)#
R10(config-if)# interface Loopback2
R10(config-if)# ip address 10.0.202.10 255.255.255.255
R10(config-if)# no shutdown

 

Task 2: Configure OSPF according to the table above.

R1(config)# router ospf 1
R1(config-router)# router-id 1.1.1.1
R1(config-router)# network 10.0.12.1 0.0.0.0 area 0
R1(config-router)# network 10.0.13.1 0.0.0.0 area 13489
R1(config-router)# network 10.0.14.1 0.0.0.0 area 13489
R1(config-router)# network 10.0.18.1 0.0.0.0 area 0
R1(config-router)# network 10.0.110.1 0.0.0.0 area 1
R1(config-router)# network 10.0.111.1 0.0.0.0 area 1
R1(config-router)# network 10.0.112.1 0.0.0.0 area 1

R2(config)# router ospf 1
R2(config-router)# router-id 2.2.2.2
R2(config-router)# network 10.0.12.2 0.0.0.0 area 0
R2(config-router)# network 10.0.25.2 0.0.0.0 area 25
R2(config-router)# network 10.0.120.2 0.0.0.0 area 2
R2(config-router)# network 10.0.121.2 0.0.0.0 area 2
R2(config-router)# network 10.0.122.2 0.0.0.0 area 2

R3(config)# router ospf 1
R3(config-router)# router-id 3.3.3.3
R3(config-router)# network 10.0.13.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.34.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.38.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.39.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.130.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.131.3 0.0.0.0 area 13489
R3(config-router)# network 10.0.132.3 0.0.0.0 area 13489

R4(config)# router ospf 1
R4(config-router)# router-id 4.4.4.4
R4(config-router)# network 10.0.14.4 0.0.0.0 area 13489
R4(config-router)# network 10.0.34.4 0.0.0.0 area 13489
R4(config-router)# network 10.0.142.4 0.0.0.0 area 13489

R5(config)# router ospf 1
R5(config-router)# router-id 5.5.5.5
R5(config-router)# network 10.0.25.5 0.0.0.0 area 25
R5(config-router)# network 10.0.150.5 0.0.0.0 area 25
R5(config-router)# network 10.0.151.5 0.0.0.0 area 25
R5(config-router)# network 10.0.152.5 0.0.0.0 area 25

R8(config)# router ospf 1
R8(config-router)# router-id 8.8.8.8
R8(config-router)# network 10.0.18.8 0.0.0.0 area 0
R8(config-router)# network 10.0.38.8 0.0.0.0 area 13489
R8(config-router)# network 10.0.89.8 0.0.0.0 area 89
R8(config-router)# network 10.0.180.8 0.0.0.0 area 8
R8(config-router)# network 10.0.181.8 0.0.0.0 area 8
R8(config-router)# network 10.0.182.8 0.0.0.0 area 8

R9(config)# router ospf 1
R9(config-router)# router-id 9.9.9.9
R9(config-router)# network 10.0.39.9 0.0.0.0 area 13489
R9(config-router)# network 10.0.89.9 0.0.0.0 area 89
R9(config-router)# network 10.0.100.9 0.0.0.0 area 91
R9(config-router)# network 10.0.190.9 0.0.0.0 area 89
R9(config-router)# network 10.0.191.9 0.0.0.0 area 89
R9(config-router)# network 10.0.192.9 0.0.0.0 area 89

R10(config)# router ospf 1
R10(config-router)# router-id 10.10.10.10
R10(config-router)# network 10.0.100.10 0.0.0.0 area 91
R10(config-router)# network 10.0.200.10 0.0.0.0 area 91
R10(config-router)# network 10.0.201.10 0.0.0.0 area 91
R10(config-router)# network 10.0.202.10 0.0.0.0 area 91

To verify the solution, use the show ip ospf neighbor command to check that OSPF adjacencies have been established between neighbors.

The OSPF autonomous system includes 8 routers. According to the network diagram, we should have 10 OSPF adjacencies established. In fact, the show ip ospf neighbor command outputs below state that routers built up 10 full OSPF relationships.

Router R1

R1# show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
8.8.8.8           1   FULL/BDR        00:00:35    10.0.18.8       GigabitEthernet0/8
2.2.2.2           1   FULL/DR         00:00:39    10.0.12.2       GigabitEthernet0/2
4.4.4.4           1   FULL/BDR        00:00:37    10.0.14.4       GigabitEthernet0/4
3.3.3.3           1   FULL/BDR        00:00:34    10.0.13.3       GigabitEthernet0/3

Router R2

R2# show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   FULL/BDR        00:00:35    10.0.12.1       GigabitEthernet0/1
5.5.5.5           1   FULL/BDR        00:00:34    10.0.25.5       GigabitEthernet0/5

Router R3

R3# show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
9.9.9.9           1   FULL/BDR        00:00:33    10.0.39.9       GigabitEthernet0/9
8.8.8.8           1   FULL/BDR        00:00:31    10.0.38.8       GigabitEthernet0/8
4.4.4.4           1   FULL/DR         00:00:39    10.0.34.4       GigabitEthernet0/4
1.1.1.1           1   FULL/DR         00:00:35    10.0.13.1       GigabitEthernet0/1

Router R9

R9# show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
8.8.8.8           1   FULL/BDR        00:00:35    10.0.89.8       GigabitEthernet0/8
10.10.10.10       1   FULL/DR         00:00:36    10.0.100.10     GigabitEthernet0/10
3.3.3.3           1   FULL/DR         00:00:38    10.0.39.3       GigabitEthernet0/3

Next, use the show ip route ospf command to check whether OSPF routers, except R10, have routes to all IP prefixes advertised in the OSPF routing domain.

Since router R9 is not ABR, it does not advertise area 91’s IP prefixes into other areas, and vice-versa. Therefore, R10’s routing table does not include routes outside area 91. Additionally, R1, R2, R3, R4, R5, and R8 do not have routes to area 91’s prefixes, while R9 has routes to all prefixes in the OSPF autonomous system, as shown in the show ip route command outputs below.

R1# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 34 subnets, 2 masks
C        10.0.12.0/24 is directly connected, GigabitEthernet0/2
L        10.0.12.1/32 is directly connected, GigabitEthernet0/2
C        10.0.13.0/24 is directly connected, GigabitEthernet0/3
L        10.0.13.1/32 is directly connected, GigabitEthernet0/3
C        10.0.14.0/24 is directly connected, GigabitEthernet0/4
L        10.0.14.1/32 is directly connected, GigabitEthernet0/4
C        10.0.17.0/24 is directly connected, GigabitEthernet0/7
L        10.0.17.1/32 is directly connected, GigabitEthernet0/7
C        10.0.18.0/24 is directly connected, GigabitEthernet0/8
L        10.0.18.1/32 is directly connected, GigabitEthernet0/8
O IA     10.0.25.0/24 [110/2] via 10.0.12.2, 01:16:48, GigabitEthernet0/2
O        10.0.34.0/24 [110/2] via 10.0.14.4, 01:16:38, GigabitEthernet0/4
                      [110/2] via 10.0.13.3, 01:16:06, GigabitEthernet0/3
O        10.0.38.0/24 [110/2] via 10.0.13.3, 01:17:04, GigabitEthernet0/3
O        10.0.39.0/24 [110/2] via 10.0.13.3, 01:17:04, GigabitEthernet0/3
O IA     10.0.89.0/24 [110/2] via 10.0.18.8, 01:15:22, GigabitEthernet0/8
C        10.0.110.1/32 is directly connected, Loopback0
C        10.0.111.1/32 is directly connected, Loopback1
C        10.0.112.1/32 is directly connected, Loopback2
O IA     10.0.120.2/32 [110/2] via 10.0.12.2, 01:16:48, GigabitEthernet0/2
O IA     10.0.121.2/32 [110/2] via 10.0.12.2, 01:16:48, GigabitEthernet0/2
O IA     10.0.122.2/32 [110/2] via 10.0.12.2, 01:16:48, GigabitEthernet0/2
O        10.0.130.3/32 [110/2] via 10.0.13.3, 01:17:04, GigabitEthernet0/3
O        10.0.131.3/32 [110/2] via 10.0.13.3, 01:17:04, GigabitEthernet0/3
O        10.0.132.3/32 [110/2] via 10.0.13.3, 01:17:04, GigabitEthernet0/3
O        10.0.142.4/32 [110/2] via 10.0.14.4, 01:16:38, GigabitEthernet0/4
O IA     10.0.150.5/32 [110/3] via 10.0.12.2, 01:16:21, GigabitEthernet0/2
O IA     10.0.151.5/32 [110/3] via 10.0.12.2, 01:16:21, GigabitEthernet0/2
O IA     10.0.152.5/32 [110/3] via 10.0.12.2, 01:16:21, GigabitEthernet0/2
O IA     10.0.180.8/32 [110/2] via 10.0.18.8, 01:15:22, GigabitEthernet0/8
O IA     10.0.181.8/32 [110/2] via 10.0.18.8, 01:15:22, GigabitEthernet0/8
O IA     10.0.182.8/32 [110/2] via 10.0.18.8, 01:15:22, GigabitEthernet0/8
O IA     10.0.190.9/32 [110/3] via 10.0.18.8, 01:14:40, GigabitEthernet0/8
O IA     10.0.191.9/32 [110/3] via 10.0.18.8, 01:14:40, GigabitEthernet0/8
O IA     10.0.192.9/32 [110/3] via 10.0.18.8, 01:14:40, GigabitEthernet0/8
R2# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 32 subnets, 2 masks
C        10.0.12.0/24 is directly connected, GigabitEthernet0/1
L        10.0.12.2/32 is directly connected, GigabitEthernet0/1
O IA     10.0.13.0/24 [110/2] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O IA     10.0.14.0/24 [110/2] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O        10.0.18.0/24 [110/2] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
C        10.0.25.0/24 is directly connected, GigabitEthernet0/5
L        10.0.25.2/32 is directly connected, GigabitEthernet0/5
C        10.0.26.0/24 is directly connected, GigabitEthernet0/6
L        10.0.26.2/32 is directly connected, GigabitEthernet0/6
O IA     10.0.34.0/24 [110/3] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O IA     10.0.38.0/24 [110/3] via 10.0.12.1, 01:23:00, GigabitEthernet0/1
O IA     10.0.39.0/24 [110/3] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O IA     10.0.89.0/24 [110/3] via 10.0.12.1, 01:23:00, GigabitEthernet0/1
O IA     10.0.110.1/32 [110/2] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O IA     10.0.111.1/32 [110/2] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O IA     10.0.112.1/32 [110/2] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
C        10.0.120.2/32 is directly connected, Loopback0
C        10.0.121.2/32 is directly connected, Loopback1
C        10.0.122.2/32 is directly connected, Loopback2
O IA     10.0.130.3/32 [110/3] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O IA     10.0.131.3/32 [110/3] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O IA     10.0.132.3/32 [110/3] via 10.0.12.1, 01:24:31, GigabitEthernet0/1
O IA     10.0.142.4/32 [110/3] via 10.0.12.1, 01:24:21, GigabitEthernet0/1
O        10.0.150.5/32 [110/2] via 10.0.25.5, 01:24:04, GigabitEthernet0/5
O        10.0.151.5/32 [110/2] via 10.0.25.5, 01:24:04, GigabitEthernet0/5
O        10.0.152.5/32 [110/2] via 10.0.25.5, 01:24:04, GigabitEthernet0/5
O IA     10.0.180.8/32 [110/3] via 10.0.12.1, 01:23:00, GigabitEthernet0/1
O IA     10.0.181.8/32 [110/3] via 10.0.12.1, 01:23:00, GigabitEthernet0/1
O IA     10.0.182.8/32 [110/3] via 10.0.12.1, 01:23:00, GigabitEthernet0/1
O IA     10.0.190.9/32 [110/4] via 10.0.12.1, 01:22:23, GigabitEthernet0/1
O IA     10.0.191.9/32 [110/4] via 10.0.12.1, 01:22:23, GigabitEthernet0/1
O IA     10.0.192.9/32 [110/4] via 10.0.12.1, 01:22:23, GigabitEthernet0/1
R3# show ip route

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 32 subnets, 2 masks
O IA     10.0.12.0/24 [110/2] via 10.0.13.1, 01:25:53, GigabitEthernet0/1
C        10.0.13.0/24 is directly connected, GigabitEthernet0/1
L        10.0.13.3/32 is directly connected, GigabitEthernet0/1
O        10.0.14.0/24 [110/2] via 10.0.34.4, 01:24:52, GigabitEthernet0/4
                      [110/2] via 10.0.13.1, 01:25:53, GigabitEthernet0/1
O IA     10.0.18.0/24 [110/2] via 10.0.38.8, 01:24:18, GigabitEthernet0/8
                      [110/2] via 10.0.13.1, 01:24:08, GigabitEthernet0/1
O IA     10.0.25.0/24 [110/3] via 10.0.13.1, 01:25:30, GigabitEthernet0/1
C        10.0.34.0/24 is directly connected, GigabitEthernet0/4
L        10.0.34.3/32 is directly connected, GigabitEthernet0/4
C        10.0.38.0/24 is directly connected, GigabitEthernet0/8
L        10.0.38.3/32 is directly connected, GigabitEthernet0/8
C        10.0.39.0/24 is directly connected, GigabitEthernet0/9
L        10.0.39.3/32 is directly connected, GigabitEthernet0/9
O IA     10.0.89.0/24 [110/2] via 10.0.38.8, 01:24:18, GigabitEthernet0/8
O IA     10.0.110.1/32 [110/2] via 10.0.13.1, 01:25:53, GigabitEthernet0/1
O IA     10.0.111.1/32 [110/2] via 10.0.13.1, 01:25:53, GigabitEthernet0/1
O IA     10.0.112.1/32 [110/2] via 10.0.13.1, 01:25:53, GigabitEthernet0/1
O IA     10.0.120.2/32 [110/3] via 10.0.13.1, 01:25:30, GigabitEthernet0/1
O IA     10.0.121.2/32 [110/3] via 10.0.13.1, 01:25:30, GigabitEthernet0/1
O IA     10.0.122.2/32 [110/3] via 10.0.13.1, 01:25:30, GigabitEthernet0/1
C        10.0.130.3/32 is directly connected, Loopback0
C        10.0.131.3/32 is directly connected, Loopback1
C        10.0.132.3/32 is directly connected, Loopback2
O        10.0.142.4/32 [110/2] via 10.0.34.4, 01:24:52, GigabitEthernet0/4
O IA     10.0.150.5/32 [110/4] via 10.0.13.1, 01:25:07, GigabitEthernet0/1
O IA     10.0.151.5/32 [110/4] via 10.0.13.1, 01:25:07, GigabitEthernet0/1
O IA     10.0.152.5/32 [110/4] via 10.0.13.1, 01:25:07, GigabitEthernet0/1
O IA     10.0.180.8/32 [110/2] via 10.0.38.8, 01:24:18, GigabitEthernet0/8
O IA     10.0.181.8/32 [110/2] via 10.0.38.8, 01:24:18, GigabitEthernet0/8
O IA     10.0.182.8/32 [110/2] via 10.0.38.8, 01:24:18, GigabitEthernet0/8
O IA     10.0.190.9/32 [110/3] via 10.0.38.8, 01:23:26, GigabitEthernet0/8
O IA     10.0.191.9/32 [110/3] via 10.0.38.8, 01:23:26, GigabitEthernet0/8
O IA     10.0.192.9/32 [110/3] via 10.0.38.8, 01:23:26, GigabitEthernet0/8
R4# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 34 subnets, 2 masks
O IA     10.0.12.0/24 [110/2] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
O        10.0.13.0/24 [110/2] via 10.0.34.3, 01:26:27, GigabitEthernet0/3
                      [110/2] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
C        10.0.14.0/24 is directly connected, GigabitEthernet0/1
L        10.0.14.4/32 is directly connected, GigabitEthernet0/1
O IA     10.0.18.0/24 [110/2] via 10.0.14.1, 01:25:43, GigabitEthernet0/1
O IA     10.0.25.0/24 [110/3] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
C        10.0.34.0/24 is directly connected, GigabitEthernet0/3
L        10.0.34.4/32 is directly connected, GigabitEthernet0/3
O        10.0.38.0/24 [110/2] via 10.0.34.3, 01:26:27, GigabitEthernet0/3
O        10.0.39.0/24 [110/2] via 10.0.34.3, 01:26:27, GigabitEthernet0/3
C        10.0.47.0/24 is directly connected, GigabitEthernet0/7
L        10.0.47.4/32 is directly connected, GigabitEthernet0/7
O IA     10.0.89.0/24 [110/3] via 10.0.34.3, 01:25:53, GigabitEthernet0/3
                      [110/3] via 10.0.14.1, 01:25:43, GigabitEthernet0/1
O IA     10.0.110.1/32 [110/2] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
O IA     10.0.111.1/32 [110/2] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
O IA     10.0.112.1/32 [110/2] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
O IA     10.0.120.2/32 [110/3] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
O IA     10.0.121.2/32 [110/3] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
O IA     10.0.122.2/32 [110/3] via 10.0.14.1, 01:27:07, GigabitEthernet0/1
O        10.0.130.3/32 [110/2] via 10.0.34.3, 01:26:27, GigabitEthernet0/3
O        10.0.131.3/32 [110/2] via 10.0.34.3, 01:26:27, GigabitEthernet0/3
O        10.0.132.3/32 [110/2] via 10.0.34.3, 01:26:27, GigabitEthernet0/3
C        10.0.140.4/32 is directly connected, Loopback0
C        10.0.141.4/32 is directly connected, Loopback1
C        10.0.142.4/32 is directly connected, Loopback2
O IA     10.0.150.5/32 [110/4] via 10.0.14.1, 01:26:42, GigabitEthernet0/1
O IA     10.0.151.5/32 [110/4] via 10.0.14.1, 01:26:42, GigabitEthernet0/1
O IA     10.0.152.5/32 [110/4] via 10.0.14.1, 01:26:42, GigabitEthernet0/1
O IA     10.0.180.8/32 [110/3] via 10.0.34.3, 01:25:53, GigabitEthernet0/3
                       [110/3] via 10.0.14.1, 01:25:43, GigabitEthernet0/1
O IA     10.0.181.8/32 [110/3] via 10.0.34.3, 01:25:53, GigabitEthernet0/3
                       [110/3] via 10.0.14.1, 01:25:43, GigabitEthernet0/1
O IA     10.0.182.8/32 [110/3] via 10.0.34.3, 01:25:53, GigabitEthernet0/3
                       [110/3] via 10.0.14.1, 01:25:43, GigabitEthernet0/1
O IA     10.0.190.9/32 [110/4] via 10.0.34.3, 01:25:01, GigabitEthernet0/3
                       [110/4] via 10.0.14.1, 01:25:01, GigabitEthernet0/1
O IA     10.0.191.9/32 [110/4] via 10.0.34.3, 01:25:01, GigabitEthernet0/3
                       [110/4] via 10.0.14.1, 01:25:01, GigabitEthernet0/1
O IA     10.0.192.9/32 [110/4] via 10.0.34.3, 01:25:01, GigabitEthernet0/3
                       [110/4] via 10.0.14.1, 01:25:01, GigabitEthernet0/1
R5# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 29 subnets, 2 masks
O IA     10.0.12.0/24 [110/2] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.13.0/24 [110/3] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.14.0/24 [110/3] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.18.0/24 [110/3] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
C        10.0.25.0/24 is directly connected, GigabitEthernet0/2
L        10.0.25.5/32 is directly connected, GigabitEthernet0/2
O IA     10.0.34.0/24 [110/4] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.38.0/24 [110/4] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.39.0/24 [110/4] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.89.0/24 [110/4] via 10.0.25.2, 01:27:06, GigabitEthernet0/2
O IA     10.0.110.1/32 [110/3] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.111.1/32 [110/3] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.112.1/32 [110/3] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.120.2/32 [110/2] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.121.2/32 [110/2] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.122.2/32 [110/2] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.130.3/32 [110/4] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.131.3/32 [110/4] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.132.3/32 [110/4] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
O IA     10.0.142.4/32 [110/4] via 10.0.25.2, 01:28:07, GigabitEthernet0/2
C        10.0.150.5/32 is directly connected, Loopback0
C        10.0.151.5/32 is directly connected, Loopback1
C        10.0.152.5/32 is directly connected, Loopback2
O IA     10.0.180.8/32 [110/4] via 10.0.25.2, 01:27:06, GigabitEthernet0/2
O IA     10.0.181.8/32 [110/4] via 10.0.25.2, 01:27:06, GigabitEthernet0/2
O IA     10.0.182.8/32 [110/4] via 10.0.25.2, 01:27:06, GigabitEthernet0/2
O IA     10.0.190.9/32 [110/5] via 10.0.25.2, 01:26:28, GigabitEthernet0/2
O IA     10.0.191.9/32 [110/5] via 10.0.25.2, 01:26:28, GigabitEthernet0/2
O IA     10.0.192.9/32 [110/5] via 10.0.25.2, 01:26:28, GigabitEthernet0/2
R8# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 31 subnets, 2 masks
O        10.0.12.0/24 [110/2] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O        10.0.13.0/24 [110/2] via 10.0.38.3, 01:28:59, GigabitEthernet0/3
O        10.0.14.0/24 [110/3] via 10.0.38.3, 01:28:59, GigabitEthernet0/3
C        10.0.18.0/24 is directly connected, GigabitEthernet0/1
L        10.0.18.8/32 is directly connected, GigabitEthernet0/1
O IA     10.0.25.0/24 [110/3] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O        10.0.34.0/24 [110/2] via 10.0.38.3, 01:28:59, GigabitEthernet0/3
C        10.0.38.0/24 is directly connected, GigabitEthernet0/3
L        10.0.38.8/32 is directly connected, GigabitEthernet0/3
O        10.0.39.0/24 [110/2] via 10.0.38.3, 01:28:59, GigabitEthernet0/3
C        10.0.89.0/24 is directly connected, GigabitEthernet0/9
L        10.0.89.8/32 is directly connected, GigabitEthernet0/9
O IA     10.0.110.1/32 [110/2] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O IA     10.0.111.1/32 [110/2] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O IA     10.0.112.1/32 [110/2] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O IA     10.0.120.2/32 [110/3] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O IA     10.0.121.2/32 [110/3] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O IA     10.0.122.2/32 [110/3] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O        10.0.130.3/32 [110/2] via 10.0.38.3, 01:28:59, GigabitEthernet0/3
O        10.0.131.3/32 [110/2] via 10.0.38.3, 01:28:59, GigabitEthernet0/3
O        10.0.132.3/32 [110/2] via 10.0.38.3, 01:28:59, GigabitEthernet0/3
O        10.0.142.4/32 [110/3] via 10.0.38.3, 01:28:59, GigabitEthernet0/3
O IA     10.0.150.5/32 [110/4] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O IA     10.0.151.5/32 [110/4] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
O IA     10.0.152.5/32 [110/4] via 10.0.18.1, 01:28:59, GigabitEthernet0/1
C        10.0.180.8/32 is directly connected, Loopback0
C        10.0.181.8/32 is directly connected, Loopback1
C        10.0.182.8/32 is directly connected, Loopback2
O        10.0.190.9/32 [110/2] via 10.0.89.9, 01:28:14, GigabitEthernet0/9
O        10.0.191.9/32 [110/2] via 10.0.89.9, 01:28:14, GigabitEthernet0/9
O        10.0.192.9/32 [110/2] via 10.0.89.9, 01:28:14, GigabitEthernet0/9
R9# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 35 subnets, 2 masks
O IA     10.0.12.0/24 [110/3] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                      [110/3] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O        10.0.13.0/24 [110/2] via 10.0.39.3, 01:29:50, GigabitEthernet0/3
O        10.0.14.0/24 [110/3] via 10.0.39.3, 01:29:50, GigabitEthernet0/3
O IA     10.0.18.0/24 [110/2] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
O IA     10.0.25.0/24 [110/4] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                      [110/4] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O        10.0.34.0/24 [110/2] via 10.0.39.3, 01:29:50, GigabitEthernet0/3
O        10.0.38.0/24 [110/2] via 10.0.39.3, 01:29:50, GigabitEthernet0/3
C        10.0.39.0/24 is directly connected, GigabitEthernet0/3
L        10.0.39.9/32 is directly connected, GigabitEthernet0/3
C        10.0.89.0/24 is directly connected, GigabitEthernet0/8
L        10.0.89.9/32 is directly connected, GigabitEthernet0/8
C        10.0.100.0/24 is directly connected, GigabitEthernet0/10
L        10.0.100.9/32 is directly connected, GigabitEthernet0/10
O IA     10.0.110.1/32 [110/3] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/3] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O IA     10.0.111.1/32 [110/3] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/3] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O IA     10.0.112.1/32 [110/3] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/3] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O IA     10.0.120.2/32 [110/4] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/4] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O IA     10.0.121.2/32 [110/4] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/4] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O IA     10.0.122.2/32 [110/4] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/4] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O        10.0.130.3/32 [110/2] via 10.0.39.3, 01:29:50, GigabitEthernet0/3
O        10.0.131.3/32 [110/2] via 10.0.39.3, 01:29:50, GigabitEthernet0/3
O        10.0.132.3/32 [110/2] via 10.0.39.3, 01:29:50, GigabitEthernet0/3
O        10.0.142.4/32 [110/3] via 10.0.39.3, 01:29:50, GigabitEthernet0/3
O IA     10.0.150.5/32 [110/5] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/5] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O IA     10.0.151.5/32 [110/5] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/5] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O IA     10.0.152.5/32 [110/5] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
                       [110/5] via 10.0.39.3, 01:29:06, GigabitEthernet0/3
O IA     10.0.180.8/32 [110/2] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
O IA     10.0.181.8/32 [110/2] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
O IA     10.0.182.8/32 [110/2] via 10.0.89.8, 01:29:20, GigabitEthernet0/8
C        10.0.190.9/32 is directly connected, Loopback0
C        10.0.191.9/32 is directly connected, Loopback1
C        10.0.192.9/32 is directly connected, Loopback2
O        10.0.200.10/32 [110/2] via 10.0.100.10, 01:29:06, GigabitEthernet0/10
O        10.0.201.10/32 [110/2] via 10.0.100.10, 01:29:06, GigabitEthernet0/10
O        10.0.202.10/32 [110/2] via 10.0.100.10, 01:29:06, GigabitEthernet0/10
R10# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
C        10.0.100.0/24 is directly connected, GigabitEthernet0/9
L        10.0.100.10/32 is directly connected, GigabitEthernet0/9
C        10.0.200.10/32 is directly connected, Loopback0
C        10.0.201.10/32 is directly connected, Loopback1
C        10.0.202.10/32 is directly connected, Loopback2

 

Task 3: Configure EIGRP according to the table above. Disable automatic summarization.

R1(config)# router eigrp 100
R1(config-router)# network 10.0.17.1 0.0.0.0
R1(config-router)# no auto-summary
R2(config)# router eigrp 200
R2(config-router)# network 10.0.26.2 0.0.0.0
R2(config-router)# no auto-summary
R4(config)# router eigrp 100
R4(config-router)# network 10.0.47.4 0.0.0.0
R4(config-router)# network 10.0.140.4 0.0.0.0
R4(config-router)# network 10.0.141.4 0.0.0.0
R4(config-router)# no auto-summary
R6(config)# router eigrp 200
R6(config-router)# network 10.0.26.6 0.0.0.0
R6(config-router)# network 10.0.160.6 0.0.0.0
R6(config-router)# network 10.0.161.6 0.0.0.0
R6(config-router)# network 10.0.162.6 0.0.0.0
R6(config-router)# no auto-summary
R7(config)# router eigrp 100
R7(config-router)# network 10.0.17.7 0.0.0.0
R7(config-router)# network 10.0.47.7 0.0.0.0
R7(config-router)# network 10.0.170.7 0.0.0.0
R7(config-router)# network 10.0.171.7 0.0.0.0
R7(config-router)# network 10.0.172.7 0.0.0.0
R7(config-router)# no auto-summary

To verify the configuration, use the show ip eigrp neighbors and show ip route  eigrp commands.

R1# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
0   10.0.17.7               Gi0/7                    12 00:05:36   16   100  0  5
R1# show ip route eigrp
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 40 subnets, 2 masks
D        10.0.47.0/24 [90/3072] via 10.0.17.7, 00:07:08, GigabitEthernet0/7
D        10.0.140.4/32 [90/131072] via 10.0.17.7, 00:07:08, GigabitEthernet0/7
D        10.0.141.4/32 [90/131072] via 10.0.17.7, 00:07:08, GigabitEthernet0/7
D        10.0.170.7/32 [90/130816] via 10.0.17.7, 00:07:08, GigabitEthernet0/7
D        10.0.171.7/32 [90/130816] via 10.0.17.7, 00:07:08, GigabitEthernet0/7
D        10.0.172.7/32 [90/130816] via 10.0.17.7, 00:07:08, GigabitEthernet0/7
R2# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(200)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
0   10.0.26.6               Gi0/6                    10 00:10:40 1589  5000  0  2
R2# show ip route eigrp
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 35 subnets, 2 masks
D        10.0.160.6/32 [90/130816] via 10.0.26.6, 00:10:46, GigabitEthernet0/6
D        10.0.161.6/32 [90/130816] via 10.0.26.6, 00:10:46, GigabitEthernet0/6
D        10.0.162.6/32 [90/130816] via 10.0.26.6, 00:10:46, GigabitEthernet0/6
R4# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
0   10.0.47.7               Gi0/7                    11 00:14:17 1589  5000  0  3
R4# show ip route eigrp
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 38 subnets, 2 masks
D        10.0.17.0/24 [90/3072] via 10.0.47.7, 00:14:22, GigabitEthernet0/7
D        10.0.170.7/32 [90/130816] via 10.0.47.7, 00:14:22, GigabitEthernet0/7
D        10.0.171.7/32 [90/130816] via 10.0.47.7, 00:14:22, GigabitEthernet0/7
D        10.0.172.7/32 [90/130816] via 10.0.47.7, 00:14:22, GigabitEthernet0/7
R6# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(200)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
0   10.0.26.2               Gi0/2                    12 00:15:36   12   100  0  3
R6# show ip route eigrp
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

R6#
R7# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H   Address                 Interface              Hold Uptime   SRTT   RTO  Q  Seq
                                                   (sec)         (ms)       Cnt Num
1   10.0.17.1               Gi0/1                    13 00:17:25   12   100  0  3
0   10.0.47.4               Gi0/4                    10 00:18:12   12   100  0  4
R7# show ip route eigrp
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
D        10.0.140.4/32 [90/130816] via 10.0.47.4, 00:18:16, GigabitEthernet0/4
D        10.0.141.4/32 [90/130816] via 10.0.47.4, 00:18:16, GigabitEthernet0/4

 

Task 4: Redistribute between EIGRP 200 and OSPF.

Router R2

R2(config)# router ospf 1
R2(config-router)# redistribute eigrp 200 subnets
R2(config-router)# exit
R2(config)# 
R2(config)# router eigrp 200
R2(config-router)# redistribute ospf 1 metric 1 1 1 1 1

To verify the configuration, it is enough to check that router R1 learned EIGRP 200 prefixes, and router R6 learned OSPF prefixes, except those in area 91.
Router R1

R1# show ip route | include E2
       E1 - OSPF external type 1, E2 - OSPF external type 2
O E2     10.0.26.0/24 [110/20] via 10.0.12.2, 00:03:08, GigabitEthernet0/2
O E2     10.0.160.6/32 [110/20] via 10.0.12.2, 00:03:08, GigabitEthernet0/2
O E2     10.0.161.6/32 [110/20] via 10.0.12.2, 00:03:08, GigabitEthernet0/2
O E2     10.0.162.6/32 [110/20] via 10.0.12.2, 00:03:08, GigabitEthernet0/2

Router R6

R6# show ip route | include D EX
D EX     10.0.12.0/24 
D EX     10.0.13.0/24 
D EX     10.0.14.0/24 
D EX     10.0.18.0/24 
D EX     10.0.25.0/24 
D EX     10.0.34.0/24 
D EX     10.0.38.0/24 
D EX     10.0.39.0/24 
D EX     10.0.89.0/24 
D EX     10.0.110.1/32 
D EX     10.0.111.1/32 
D EX     10.0.112.1/32 
D EX     10.0.120.2/32 
D EX     10.0.121.2/32 
D EX     10.0.122.2/32 
D EX     10.0.130.3/32 
D EX     10.0.131.3/32 
D EX     10.0.132.3/32 
D EX     10.0.142.4/32 
D EX     10.0.150.5/32 
D EX     10.0.151.5/32 
D EX     10.0.152.5/32 
D EX     10.0.180.8/32 
D EX     10.0.181.8/32 
D EX     10.0.182.8/32 
D EX     10.0.190.9/32 
D EX     10.0.191.9/32 
D EX     10.0.192.9/32

 

Task 5: Configure area 13489 as a stub area.

R1(config)# router ospf 1
R1(config-router)# area 13489 stub
R3(config)# router ospf 1
R3(config-router)# area 13489 stub
R4(config)# router ospf 1
R4(config-router)# area 13489 stub
R8(config)# router ospf 1
R8(config-router)# area 13489 stub
R9(config)# router ospf 1
R9(config-router)# area 13489 stub

To verify the configuration, issue the show ip ospf command on routers R1, R3, R4, R8, and R9.

R1# show ip ospf | begin Area 13489
    Area 13489
        Number of interfaces in this area is 2
        It is a stub area
        Generates stub default route with cost 1
        Area has no authentication
        SPF algorithm last executed 00:05:19.726 ago
        SPF algorithm executed 15 times
        Area ranges are
        Number of LSA 50. Checksum Sum 0x1AC26F
        Number of opaque link LSA 0. Checksum Sum 0x000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0
R3# show ip ospf | begin Area 13489
    Area 13489
        Number of interfaces in this area is 7 (3 loopback)
        It is a stub area
        Area has no authentication
        SPF algorithm last executed 00:06:38.082 ago
        SPF algorithm executed 11 times
        Area ranges are
        Number of LSA 50. Checksum Sum 0x1AC26F
        Number of opaque link LSA 0. Checksum Sum 0x000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0
R4# show ip ospf | begin Area 13489
    Area 13489
        Number of interfaces in this area is 3 (1 loopback)
        It is a stub area
        Area has no authentication
        SPF algorithm last executed 00:06:40.725 ago
        SPF algorithm executed 11 times
        Area ranges are
        Number of LSA 50. Checksum Sum 0x1AC26F
        Number of opaque link LSA 0. Checksum Sum 0x000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0
R8# show ip ospf | begin Area 13489
    Area 13489
        Number of interfaces in this area is 1
        It is a stub area
        Generates stub default route with cost 1
        Area has no authentication
        SPF algorithm last executed 00:06:39.272 ago
        SPF algorithm executed 9 times
        Area ranges are
        Number of LSA 50. Checksum Sum 0x1AC26F
        Number of opaque link LSA 0. Checksum Sum 0x000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0
R9# show ip ospf | begin Area 13489
    Area 13489
        Number of interfaces in this area is 1
        It is a stub area
        Area has no authentication
        SPF algorithm last executed 00:06:51.292 ago
        SPF algorithm executed 4 times
        Area ranges are
        Number of LSA 50. Checksum Sum 0x1AC26F
        Number of opaque link LSA 0. Checksum Sum 0x000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0

All non-ABR routers in area 13489 installed a default route in their routing tables. R3 and R4 no longer have external routes in their routing tables, while R9 still does because it gets them from R8 through area 89, as you can see in the show ip route command outputs below.

Router R3

R3# show ip route | include E2|/0
       E1 - OSPF external type 1, E2 - OSPF external type 2
O*IA  0.0.0.0/0 [110/2] via 10.0.38.8, 00:04:54, GigabitEthernet0/8

Router R4

R4# show ip route | include E2|/0
       E1 - OSPF external type 1, E2 - OSPF external type 2
O*IA  0.0.0.0/0 [110/2] via 10.0.14.1, 00:05:12, GigabitEthernet0/1

Router R9

R9# show ip route | include E2|/0
       E1 - OSPF external type 1, E2 - OSPF external type 2
O*IA  0.0.0.0/0 [110/3] via 10.0.39.3, 00:04:33, GigabitEthernet0/3
O E2     10.0.26.0/24 [110/20] via 10.0.89.8, 00:04:43, GigabitEthernet0/8
O E2     10.0.160.6/32 [110/20] via 10.0.89.8, 00:04:43, GigabitEthernet0/8
O E2     10.0.161.6/32 [110/20] via 10.0.89.8, 00:04:43, GigabitEthernet0/8
O E2     10.0.162.6/32 [110/20] via 10.0.89.8, 00:04:43, GigabitEthernet0/8

 

Task 6: Redistribute between EIGRP 100 and OSPF.

Router R1

R1(config)# router ospf 1
R1(config-router)# redistribute eigrp 100 subnets
R1(config-router)# exit
R1(config)# 
R1(config)# router eigrp 100
R1(config-router)# redistribute ospf 1 metric 1 1 1 1 1

 

Task 7: Configure the network such that router R10 has access to all subnets in the network.

Router R8

R8(config)# router ospf 1
R8(config-router)# area 89 virtual-link 9.9.9.9

Router R9

R9(config)# router ospf 1
R9(config-router)# area 89 virtual-link 8.8.8.8

The show ip route command output indicates that R10 can reach all destinations in the network.

R10# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 44 subnets, 2 masks
O IA     10.0.12.0/24 [110/4] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.13.0/24 [110/3] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O IA     10.0.14.0/24 [110/4] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O E2     10.0.17.0/24 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O IA     10.0.18.0/24 [110/3] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.25.0/24 [110/5] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O E2     10.0.26.0/24 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O IA     10.0.34.0/24 [110/3] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O IA     10.0.38.0/24 [110/3] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O IA     10.0.39.0/24 [110/2] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O E2     10.0.47.0/24 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O IA     10.0.89.0/24 [110/2] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
C        10.0.100.0/24 is directly connected, GigabitEthernet0/9
L        10.0.100.10/32 is directly connected, GigabitEthernet0/9
O IA     10.0.110.1/32 [110/4] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.111.1/32 [110/4] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.112.1/32 [110/4] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.120.2/32 [110/5] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.121.2/32 [110/5] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.122.2/32 [110/5] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.130.3/32 [110/3] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O IA     10.0.131.3/32 [110/3] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O IA     10.0.132.3/32 [110/3] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O E2     10.0.140.4/32 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O E2     10.0.141.4/32 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O IA     10.0.142.4/32 [110/4] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O IA     10.0.150.5/32 [110/6] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.151.5/32 [110/6] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.152.5/32 [110/6] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O E2     10.0.160.6/32 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O E2     10.0.161.6/32 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O E2     10.0.162.6/32 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O E2     10.0.170.7/32 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O E2     10.0.171.7/32 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O E2     10.0.172.7/32 [110/20] via 10.0.100.9, 00:02:20, GigabitEthernet0/9
O IA     10.0.180.8/32 [110/3] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.181.8/32 [110/3] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.182.8/32 [110/3] via 10.0.100.9, 00:02:26, GigabitEthernet0/9
O IA     10.0.190.9/32 [110/2] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O IA     10.0.191.9/32 [110/2] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
O IA     10.0.192.9/32 [110/2] via 10.0.100.9, 00:02:30, GigabitEthernet0/9
C        10.0.200.10/32 is directly connected, Loopback0
C        10.0.201.10/32 is directly connected, Loopback1
C        10.0.202.10/32 is directly connected, Loopback2

At this point in the lab, R9 starts to advertise area 91’s prefixes. In fact, all routers have learned those prefixes, including R1.
Router R1

R1# show ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 48 subnets, 2 masks
O IA     10.0.25.0/24 [110/2] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O E2     10.0.26.0/24 [110/20] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O        10.0.34.0/24 [110/2] via 10.0.14.4, 00:26:05, GigabitEthernet0/4
                      [110/2] via 10.0.13.3, 00:26:05, GigabitEthernet0/3
O        10.0.38.0/24 [110/2] via 10.0.13.3, 00:25:54, GigabitEthernet0/3
O        10.0.39.0/24 [110/2] via 10.0.13.3, 00:25:44, GigabitEthernet0/3
O IA     10.0.89.0/24 [110/2] via 10.0.18.8, 00:26:35, GigabitEthernet0/8
O IA     10.0.100.0/24 [110/3] via 10.0.18.8, 00:04:34, GigabitEthernet0/8
O IA     10.0.120.2/32 [110/2] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O IA     10.0.121.2/32 [110/2] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O IA     10.0.122.2/32 [110/2] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O        10.0.130.3/32 [110/2] via 10.0.13.3, 00:26:15, GigabitEthernet0/3
O        10.0.131.3/32 [110/2] via 10.0.13.3, 00:26:15, GigabitEthernet0/3
O        10.0.132.3/32 [110/2] via 10.0.13.3, 00:26:15, GigabitEthernet0/3
O        10.0.142.4/32 [110/2] via 10.0.14.4, 00:26:05, GigabitEthernet0/4
O IA     10.0.150.5/32 [110/3] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O IA     10.0.151.5/32 [110/3] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O IA     10.0.152.5/32 [110/3] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O E2     10.0.160.6/32 [110/20] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O E2     10.0.161.6/32 [110/20] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O E2     10.0.162.6/32 [110/20] via 10.0.12.2, 00:26:35, GigabitEthernet0/2
O IA     10.0.180.8/32 [110/2] via 10.0.18.8, 00:26:35, GigabitEthernet0/8
O IA     10.0.181.8/32 [110/2] via 10.0.18.8, 00:26:35, GigabitEthernet0/8
O IA     10.0.182.8/32 [110/2] via 10.0.18.8, 00:26:35, GigabitEthernet0/8
O IA     10.0.190.9/32 [110/3] via 10.0.18.8, 00:04:34, GigabitEthernet0/8
O IA     10.0.191.9/32 [110/3] via 10.0.18.8, 00:04:34, GigabitEthernet0/8
O IA     10.0.192.9/32 [110/3] via 10.0.18.8, 00:04:34, GigabitEthernet0/8
O IA     10.0.200.10/32 [110/4] via 10.0.18.8, 00:04:34, GigabitEthernet0/8
O IA     10.0.201.10/32 [110/4] via 10.0.18.8, 00:04:34, GigabitEthernet0/8
O IA     10.0.202.10/32 [110/4] via 10.0.18.8, 00:04:34, GigabitEthernet0/8

 

Task 8: Configure router R3 to not install R8 and R9’s default routes in the routing table.

Router R3

R3(config)# interface range gigabitEthernet 0/8 - 9
R3(config-if-range)# ip ospf cost 2

ABRs R8 and R9 generates the default route with a cost of 1. When router R3 receives each default route it adds its path cost to the flooding router to route’s cost. After increasing the OSPF cost of the interfaces leading to R8 and R9, R1’s default route becomes the one with the lowest cost on R3, and thus gets preferred over the other default routes, as shown below.

R3# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is 10.0.13.1 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/2] via 10.0.13.1, 00:37:30, GigabitEthernet0/1
      10.0.0.0/8 is variably subnetted, 36 subnets, 2 masks


omitted output

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Related Lessons to OSPF Stub Area

Mohamed Ouamer is a computer science teacher and a self-published author. He taught networking technologies and programming for more than fifteen years. While he loves to share knowledge and write, Mohamed's best passions include spending time with his family, visiting his parents, and learning new things.