Virtual Link Configuration

ccnp-routing

Step by step OSPF virtual link configuration in a five router lab, verifying routing tables and DoNotAge LSAs, plus link authentication.

Published

Dec 8, 2017

This is an example we work on

ospf

Basic OSPF Configuration

R1:

router ospf 1
 network 12.12.12.1 0.0.0.0 area 12

R2:

router ospf 1
 network 12.12.12.2 0.0.0.0 area 12
 network 172.16.234.2 0.0.0.0 area 234

R3:

router ospf 1
 network 35.35.35.3 0.0.0.0 area 0
 network 172.16.234.3 0.0.0.0 area 234

R4:

router ospf 1
 area 234 virtual-link 2.2.2.2
 network 45.45.45.4 0.0.0.0 area 0
 network 172.16.234.4 0.0.0.0 area 234

R5:

router ospf 1
 network 10.10.0.0 0.0.7.255 area 0
 network 35.35.35.5 0.0.0.0 area 0
 network 45.45.45.5 0.0.0.0 area 0

Basic verification on R5:

Routing Table:

R5#show ip route ospf
Gateway of last resort is not set

   172.16.0.0/24 is subnetted, 1 subnets
O IA     172.16.234.0 [110/2] via 45.45.45.4, GigabitEthernet0/4
                   [110/2] via 35.35.35.3, GigabitEthernet0/3

LSDB:

R5#show ip ospf database
     OSPF Router with ID (50.5.5.5) (Process ID 1)

 Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count 3.3.3.3 3.3.3.3 616 0x80000008 0x0094A3 1 4.4.4.4 4.4.4.4 613 0x80000008 0x00B042 1 50.5.5.5 50.5.5.5 612 0x80000004 0x005037 6

    Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum 35.35.35.5 50.5.5.5 615 0x80000001 0x00A2A1 45.45.45.5 50.5.5.5 611 0x80000001 0x006BB6

    Summary Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum 172.16.234.0 3.3.3.3 607 0x80000002 0x0099ED 172.16.234.0 4.4.4.4 602 0x80000004 0x00770A

Virtual Link Configuration

R2:

R2(config)# router ospf 1
R2(config-router)#area 234 virtual-link 4.4.4.4
R2(config-router)#area 234 virtual-link 3.3.3.3

When R2 was configured, we received these console logs on R3 and R4 every 10 seconds

R3#
*Dec  9 02:27:56.261: %OSPF-4-ERRRCV: Received invalid packet: mismatched area ID from backbone area from 172.16.234.2, GigabitEthernet0/0
R3#
*Dec  9 02:28:05.558: %OSPF-4-ERRRCV: Received invalid packet: mismatched area ID from backbone area from 172.16.234.2, GigabitEthernet0/0

R4#
*Dec  9 02:29:14.726: %OSPF-4-ERRRCV: Received invalid packet: mismatched area ID from backbone area from 172.16.234.2, GigabitEthernet0/0
R4#
*Dec  9 02:29:24.691: %OSPF-4-ERRRCV: Received invalid packet: mismatched area ID from backbone area from 172.16.234.2, GigabitEthernet0/0

R3:

R3(config)#router ospf 1
R3(config-router)#area 234 virtual-link 2.2.2.2
*Dec  9 02:31:02.743: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on OSPF_VL1 from LOADING to FULL, Loading Done

Then we no longer received the console log for R3 but R4 still had it every 10 seconds

For now let us look at the tables on R5

R5#show ip route ospf
Gateway of last resort is not set

    12.0.0.0/30 is subnetted, 1 subnets
O IA     12.12.12.0 [110/3] via 35.35.35.3, GigabitEthernet0/3
    172.16.0.0/24 is subnetted, 1 subnets
O IA     172.16.234.0 [110/2] via 45.45.45.4, GigabitEthernet0/4
                    [110/2] via 35.35.35.3, GigabitEthernet0/3

R5#show ip ospf database

            OSPF Router with ID (50.5.5.5) (Process ID 1)

        Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         2     (DNA) 0x80000007 0x00055F 1
3.3.3.3         3.3.3.3         376         0x8000000B 0x00E986 2
4.4.4.4         4.4.4.4         1109        0x8000000A 0x00AC44 1
50.5.5.5        50.5.5.5        856         0x80000005 0x004E38 6

        Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
35.35.35.5      50.5.5.5        856         0x80000002 0x00A0A2
45.45.45.5      50.5.5.5        856         0x80000002 0x0069B7

        Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
12.12.12.0      2.2.2.2         65    (DNA) 0x80000001 0x00937F
172.16.234.0    2.2.2.2         65    (DNA) 0x80000001 0x00B9D2
172.16.234.0    3.3.3.3         719         0x80000003 0x0097EE
172.16.234.0    4.4.4.4         667         0x80000005 0x00750B

R4:

R4(config)#router ospf 1
R4(config-router)#area 234 virtual-link 2.2.2.2
*Dec  9 02:33:37.668: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on OSPF_VL0 from LOADING to FULL, Loading Done

Now let us check the routing table and LSDB in R5

R5#show ip route ospf
Gateway of last resort is not set

    12.0.0.0/30 is subnetted, 1 subnets
O IA     12.12.12.0 [110/3] via 45.45.45.4, GigabitEthernet0/4
                  [110/3] via 35.35.35.3, GigabitEthernet0/3
    172.16.0.0/24 is subnetted, 1 subnets
O IA     172.16.234.0 [110/2] via 45.45.45.4, GigabitEthernet0/4
                    [110/2] via 35.35.35.3, GigabitEthernet0/3

R5#show ip ospf database

            OSPF Router with ID (50.5.5.5) (Process ID 1)

        Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         2     (DNA) 0x80000003 0x00F8A3 2
3.3.3.3         3.3.3.3         455         0x80000003 0x003048 2
4.4.4.4         4.4.4.4         353         0x80000003 0x00032F 2
50.5.5.5        50.5.5.5        470         0x80000003 0x005236 6

        Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
35.35.35.5      50.5.5.5        470         0x80000001 0x00A2A1
45.45.45.5      50.5.5.5        475         0x80000001 0x006BB6

        Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
12.12.12.0      2.2.2.2         12    (DNA) 0x80000001 0x00937F
172.16.234.0    2.2.2.2         12    (DNA) 0x80000001 0x00B9D2
172.16.234.0    3.3.3.3         507         0x80000001 0x009BEC
172.16.234.0    4.4.4.4         514         0x80000001 0x007D07

R5#ping 12.12.12.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 12.12.12.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/11 ms

Authentication

Customer’s requirement:
1. R2 and R3 authenticate each other using clear text
2. R2 and R4 authenticate each other using MD5

R2(config-router)#area 234 virtual-link 3.3.3.3 authentication-key cisco
R2(config-router)#area 234 virtual-link 4.4.4.4 authentication message-digest-key 89 md5 cisco

R3(config-router)#area 234 virtual-link 2.2.2.2 authentication-key cisco

R4(config-router)#area 234 virtual-link 2.2.2.2 authentication message-digest-key 89 md5 cisco