Virtual Link

In OSPF (Open Shortest Path First) for IPv6, a Virtual Link is a logical connection established between two OSPF routers across a non-backbone area, enabling the creation of a virtual path through that non-backbone area. This mechanism is particularly useful when a router in an OSPF Autonomous System (AS) is not directly connected to the backbone area (Area 0). The Virtual Link allows the routers to exchange routing information and maintain OSPF adjacency, essentially "virtually" connecting them through the non-backbone area. The configuration involves specifying the router IDs of the connecting routers and ensuring a consistent OSPF area ID. Virtual Links play a critical role in preserving OSPF network connectivity, especially in scenarios where a direct physical connection to the backbone is impractical or undesirable.

Lab:

Disclaimer

This Configuration Guide is designed to assist members to enhance their skills in particular technology area. While every effort has been made to ensure that all material is as complete and accurate as possible, the enclosed material is presented on an Dzas isdz basis. Neither the authors nor Forum assume any liability or responsibility to any person or entity with respect to loss or damages incurred from the information contained in this guide. This configuration guide was developed by Forum. Any similarities between material presented in this configuration guide and any other material is completely coincidental.

Cisco IOS Software, Linux Software (I86BI_LINUX-ADVENTERPRISEK9-M), Version 15.2(4)M1, DEVELOPMENT TEST SOFTWARE

Task 1: Configure IPv6 OSPF Virtual Link

Step 1: In the configuration mode of router configure IPv6 OSPF Process for Virtual Link by following command:

R1:
ipv6 router ospf 1
interface s2/0
ipv6 ospf 1 area 0
interface loop1
ipv6 ospf 1 area 0
interface loop2
ipv6 ospf 1 area 0
interface loop3
ipv6 ospf 1 area 0
exit

R2:
interface s2/0
ipv6 ospf 2 area 0
interface loop1
ipv6 ospf 2 area 1
interface loop2
ipv6 ospf 2 area 1
interface loop3
ipv6 ospf 2 area 1
interface e0/0
ipv6 ospf 2 area 1
exit

R3:
ipv6 router ospf 3
interface s2/0
ipv6 ospf 3 area 2
interface e0/0
ipv6 ospf 3 area 1
interface loop1
ipv6 ospf 3 area 1
interface loop2
ipv6 ospf 3 area 1
interface loop3
ipv6 ospf 3 area 1
exit

R4:
ipv6 router ospf 4
interface s2/0
ipv6 ospf 4 area 2
interface loop1
ipv6 ospf 4 area 2
interface loop2
ipv6 ospf 4 area 2
interface loop3
ipv6 ospf 4 area 2
exit

R4#show ipv6 route
IPv6 Routing Table - default - 9 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
       B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP
       H - NHRP, I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
       IS - ISIS summary, D - EIGRP, EX - EIGRP external, NM - NEMO
       ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect
       O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
       ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2, l - LISP
C   34::/64 [0/0]
     via Serial2/0, directly connected
L   34::A8BB:CCFF:FE00:400/128 [0/0]
     via Serial2/0, receive
C   44:0:1::/64 [0/0]
     via Loopback1, directly connected
L   44:0:1::4/128 [0/0]
     via Loopback1, receive
C   44:0:2::/64 [0/0]
     via Loopback2, directly connected
L   44:0:2::4/128 [0/0]
     via Loopback2, receive
C   44:0:3::/64 [0/0]
     via Loopback3, directly connected
L   44:0:3::4/128 [0/0]
via Loopback3, receive
L   FF00::/8 [0/0]
     via Null0, receive

Step 2: Configure IPv6 OSPF Virtual Link

R2:
ipv6 router ospf 2
area 1 virtual-link 33.0.3.3
exit

R3:
ipv6 router ospf 3
area 1 virtual-link 22.0.3.2
exit

Task 2: Verification:

Step 3: Verify virtual link in IPv6 OSPF process

R3#show ipv6 ospf virtual-link
OSPFv3 Router with ID (33.0.3.3) (Process ID 3)

Virtual Link OSPFv3_VL0 to router 22.0.3.2 is up
Interface ID 21, IPv6 address 22:0:1::2
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface Ethernet0/0, Cost of using 10
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Adjacency State FULL (Hello suppressed)
Index 1/1/3, retransmission queue length 0, number of retransmission 0
First 0x0(0)/0x0(0)/0x0(0) Next 0x0(0)/0x0(0)/0x0(0)
Last retransmission scan length is 0, maximum is 0
Last retransmission scan time is 0 msec, maximum is 0 msec

Step 4: Verify routes on R1 & R4 router’s routing table

R1#show ipv6 route
IPv6 Routing Table - default - 20 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
       B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP
       H - NHRP, I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
       IS - ISIS summary, D - EIGRP, EX - EIGRP external, NM - NEMO
       ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect
       O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
       ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2, l - LISP
C   11:0:1::/64 [0/0]
     via Loopback1, directly connected
L   11:0:1::1/128 [0/0]
     via Loopback1, receive
C   11:0:2::/64 [0/0]
     via Loopback2, directly connected
L   11:0:2::1/128 [0/0]
     via Loopback2, receive
C   11:0:3::/64 [0/0]
     via Loopback3, directly connected
L   11:0:3::1/128 [0/0]
     via Loopback3, receive
C   12::/64 [0/0]
     via Serial2/0, directly connected
L   12::A8BB:CCFF:FE00:100/128 [0/0]
via Serial2/0, receive
OI  22:0:1::2/128 [110/64]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  22:0:2::2/128 [110/64]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  22:0:3::2/128 [110/64]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  23::/64 [110/74]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  33:0:1::3/128 [110/74]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  33:0:2::3/128 [110/74]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  33:0:3::3/128 [110/74]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  34::/64 [110/138]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  44:0:1::4/128 [110/138]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  44:0:2::4/128 [110/138]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
OI  44:0:3::4/128 [110/138]
     via FE80::A8BB:CCFF:FE00:200, Serial2/0
L   FF00::/8 [0/0]
     via Null0, receive

IPv6 Routing Table - default - 20 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
       B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP
       H - NHRP, I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
       IS - ISIS summary, D - EIGRP, EX - EIGRP external, NM - NEMO
       ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect
       O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
       ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2, l - LISP
OI  11:0:1::1/128 [110/138]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  11:0:2::1/128 [110/138]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  11:0:3::1/128 [110/138]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  12::/64 [110/138]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  22:0:1::2/128 [110/74]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  22:0:2::2/128 [110/74]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  22:0:3::2/128 [110/74]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  23::/64 [110/74]
via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  33:0:1::3/128 [110/64]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  33:0:2::3/128 [110/64]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
OI  33:0:3::3/128 [110/64]
     via FE80::A8BB:CCFF:FE00:300, Serial2/0
C   34::/64 [0/0]
     via Serial2/0, directly connected
L   34::A8BB:CCFF:FE00:400/128 [0/0]
     via Serial2/0, receive
C   44:0:1::/64 [0/0]
     via Loopback1, directly connected
L   44:0:1::4/128 [0/0]
     via Loopback1, receive
C   44:0:2::/64 [0/0]
     via Loopback2, directly connected
L   44:0:2::4/128 [0/0]
     via Loopback2, receive
C   44:0:3::/64 [0/0]
     via Loopback3, directly connected
L   44:0:3::4/128 [0/0]
     via Loopback3, receive
L   FF00::/8 [0/0]
     via Null0, receive

R4#traceroute 11:0:1::1
Type escape sequence to abort.
Tracing the route to 11:0:1::1

  1 34::A8BB:CCFF:FE00:300 8 msec 9 msec 8 msec
  2 23::A8BB:CCFF:FE00:200 9 msec 9 msec 8 msec
  3 12::A8BB:CCFF:FE00:100 16 msec 16 msec 17 msec

Area 2 can communicate with Area 1 without connecting through Backbone area 0 with the help of Virtual Link