An Open Shortest Path First (OSPF) autonomous system all areas must be physically connected to the backbone area (Area 0). In some cases, if this is not possible, we can use a virtual link to connect to the backbone (Area 0) through a non-backbone area. We can also use the virtual links to connect two parts of a partitioned backbone (Area 0) through a non-backbone area. The area through which we configure the virtual link, known as a transit area, must have full routing information. Remember the transit area cannot be a stub area.





Virtual link must be configuring both sides with the same area ID and the corresponding virtual link OSPF neighbor router ID. Show IP OSPF neighbors command give you the router ID information.





area-id Is identifier for the OSPF area assigned to the transit area for the virtual link. OSPF area ID can be from 0 to 4294967295 or an IP address. router-id Router ID is associated with the virtual link neighbor. Specify as an IP address. The router ID appears in the show IP OSPF neighbors command.























configuration virtual link:





Topology:









GOAL:





Configure interfaces and assigned IP addresses as per the Topology

advertise the interfaces using multiple areas defined as per the Topology

configure the manual router id (RID) R1-11.1.1.1, R2-22.1.1.1, and R3-33.1.1.1

make sure that the loop-back of R1- 11.0.0.0 routes should be seen on all the other routers

R1#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet 0/0 10.1.1.1 YES manual up up

Serial3/0 1.1.1.1 YES manual up up

Loopback0 11.0.0.1 YES manual up up

Loopback1 11.0.1.1 YES manual up up

Loopback2 11.0.2.1 YES manual up up

Loopback3 11.0.3.1 YES manual up up







R2#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 20.1.1.1 YES manual up up

Serial3/0 1.1.1.2 YES manual up up

Serial3/1 2.2.2.1 YES manual up up





R3#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 30.1.1.1 YES manual up up

Serial3/1 2.2.2.2 YES manual up up

Serial3/2 3.3.3.1 YES manual up up







R4#show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 40.1.1.1 YES manual up up Serial3/2 3.3.3.2 YES manual up up Loopback0 14.0.0.1 YES manual up up Loopback1 14.0.1.1 YES manual up up Loopback2 14.0.2.1 YES manual up up Loopback3 14.0.3.1 YES manual up up





R1(config)#router ospf 1 R1(config-router)# router-id 11.1.1.1 R1(config-router)#NETwork 1.0.0.0 0.255.255.255 Area 20 R1(config-router)#NETwork 10.0.0.0 0.255.255.255 Area 20 R1(config-router)#NETwork 11.0.0.0 0.0.0.255 area 10





R2(config)#router ospf 1 R2(config-router)# router-id 22.1.1.1 R2(config-router)#network 1.0.0.0 0.255.255.255 area 20 R2(config-router)#network 2.0.0.0 0.255.255.255 area 20

R2(config-router)#network 20.0.0.0 0.255.255.255 area 20





R3(config)#router ospf 1 R3(config-router)# router-id 33.1.1.1 R3(config-router)#network 2.0.0.0 0.255.255.255 a 20 R3(config-router)#network 3.0.0.0 0.255.255.255 area 0 R3(config-router)#network 30.0.0.0 0.255.255.255 area 20





R4(config)#router ospf 1 R4(config-router)#network 3.0.0.0 0.255.255.255 area 0 R4(config-router)#network 40.0.0.0 0.255.255.255 area 0 R4(config-router)#network 14.0.0.0 0.0.0.255 area 0





R2#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 + - replicated route, % - next hop override

Gateway of last resort is not set

O IA 3.0.0.0/8 [110/128] via 2.2.2.2, 00:28:48, Serial3/1 O 10.0.0.0/8 [110/65] via 1.1.1.1, 00:31:39, Serial3/0 14.0.0.0/32 is subnetted, 1 subnets O IA 14.0.0.1 [110/129] via 2.2.2.2, 00:26:24, Serial3/1 O 30.0.0.0/8 [110/65] via 2.2.2.2, 00:29:55, Serial3/1 O IA 40.0.0.0/8 [110/129] via 2.2.2.2, 00:26:39, Serial3/1







R3#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 + - replicated route, % - next hop override

Gateway of last resort is not set

O 1.0.0.0/8 [110/128] via 2.2.2.1, 00:29:41, Serial3/1 O 10.0.0.0/8 [110/129] via 2.2.2.1, 00:29:41, Serial3/1 14.0.0.0/32 is subnetted, 1 subnets O 14.0.0.1 [110/65] via 3.3.3.2, 00:27:06, Serial3/2 O 20.0.0.0/8 [110/65] via 2.2.2.1, 00:29:41, Serial3/1 O 40.0.0.0/8 [110/65] via 3.3.3.2, 00:27:21, Serial3/2





R4#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 + - replicated route, % - next hop override

Gateway of last resort is not set

O IA 1.0.0.0/8 [110/192] via 3.3.3.1, 00:28:06, Serial3/2 O IA 2.0.0.0/8 [110/128] via 3.3.3.1, 00:28:06, Serial3/2 O IA 10.0.0.0/8 [110/193] via 3.3.3.1, 00:28:06, Serial3/2 O IA 20.0.0.0/8 [110/129] via 3.3.3.1, 00:28:06, Serial3/2 O IA 30.0.0.0/8 [110/65] via 3.3.3.1, 00:28:06, Serial3/2





No routes from 11.0.0.0 coming in to routing table of R2, R3, R3, and R4 as it belong to area 10 which in not directly connected to area 0





in order to make sure that the loopback of R1 (11.0.0.0) routes should be seen on all the other routes we need to configure Virtual-link which allows area 10 to area 0 virtually over area 20 virtual area.





R1#show ip protocols *** IP Routing is NSF aware ***

Routing Protocol is "ospf 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 11.1.1.1 Number of areas in this router is 2. 2 normal 0 stub 0 nssa Maximum path: 4 Routing for Networks: 1.0.0.0 0.255.255.255 area 20 10.0.0.0 0.255.255.255 area 20 11.0.0.0 0.0.0.255 area 10 Routing Information Sources: Gateway Distance Last Update 22.1.1.1 110 00:37:30 33.1.1.1 110 00:32:35 Distance: (default is 110)









R3#show ip protocols *** IP Routing is NSF aware ***

Routing Protocol is "ospf 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 33.1.1.1 It is an area border router Number of areas in this router is 2. 2 normal 0 stub 0 nssa Maximum path: 4 Routing for Networks: 2.0.0.0 0.255.255.255 area 20 3.0.0.0 0.255.255.255 area 0 30.0.0.0 0.255.255.255 area 20 Routing Information Sources: Gateway Distance Last Update 11.1.1.1 110 00:35:57 14.0.3.1 110 00:33:22 22.1.1.1 110 00:35:57 Distance: (default is 110)





R1(config)#router ospf 1 R1(config-router)# area 20 virtual-link 33.1.1.1





R3(config)#router ospf 1 R3(config-router)# area 20 virtual-link 11.1.1.1





R2#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 + - replicated route, % - next hop override

Gateway of last resort is not set

O IA 3.0.0.0/8 [110/128] via 2.2.2.2, 00:40:25, Serial3/1 O 10.0.0.0/8 [110/65] via 1.1.1.1, 00:43:16, Serial3/0 11.0.0.0/32 is subnetted, 1 subnets O IA 11.0.0.1 [110/65] via 1.1.1.1, 00:02:47, Serial3/0 14.0.0.0/32 is subnetted, 1 subnets O IA 14.0.0.1 [110/129] via 2.2.2.2, 00:38:01, Serial3/1 O 30.0.0.0/8 [110/65] via 2.2.2.2, 00:41:32, Serial3/1 O IA 40.0.0.0/8 [110/129] via 2.2.2.2, 00:38:16, Serial3/1







R3#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 + - replicated route, % - next hop override

Gateway of last resort is not set

O 1.0.0.0/8 [110/128] via 2.2.2.1, 00:41:43, Serial3/1 O 10.0.0.0/8 [110/129] via 2.2.2.1, 00:41:43, Serial3/1 11.0.0.0/32 is subnetted, 1 subnets O IA 11.0.0.1 [110/129] via 2.2.2.1, 00:03:18, Serial3/1 14.0.0.0/32 is subnetted, 1 subnets O 14.0.0.1 [110/65] via 3.3.3.2, 00:39:08, Serial3/2 O 20.0.0.0/8 [110/65] via 2.2.2.1, 00:41:43, Serial3/1 O 40.0.0.0/8 [110/65] via 3.3.3.2, 00:39:23, Serial3/2





R4#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 + - replicated route, % - next hop override

Gateway of last resort is not set

O IA 1.0.0.0/8 [110/192] via 3.3.3.1, 00:40:10, Serial3/2 O IA 2.0.0.0/8 [110/128] via 3.3.3.1, 00:40:10, Serial3/2 O IA 10.0.0.0/8 [110/193] via 3.3.3.1, 00:40:10, Serial3/2 11.0.0.0/32 is subnetted, 1 subnets O IA 11.0.0.1 [110/193] via 3.3.3.1, 00:03:35, Serial3/2 O IA 20.0.0.0/8 [110/129] via 3.3.3.1, 00:40:10, Serial3/2 O IA 30.0.0.0/8 [110/65] via 3.3.3.1, 00:40:10, Serial3/2









R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface 33.1.1.1 0 FULL/ - - 2.2.2.2 OSPF_VL0 22.1.1.1 0 FULL/ - 00:00:32 1.1.1.2 Serial3/0





R1#show ip ospf virtual-links Virtual Link OSPF_VL0 to router 33.1.1.1 is up Run as demand circuit DoNotAge LSA allowed. Transit area 20, via interface Serial3/0 Topology-MTID Cost Disabled Shutdown Topology Name 0 128 no no Base Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:04 Adjacency State FULL (Hello suppressed) Index 1/2, retransmission queue length 0, number of retransmission 0 First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0) Last retransmission scan length is 0, maximum is 0 Last retransmission scan time is 0 msec, maximum is 0 msec





R4#ping 11.0.0.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 11.0.0.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 80/131/172 ms

















