To configure virtual-link, enter the following command in OSPF configuration mode.
(config-router)#area <area-id> virtual-link <router-id>
<process-id> : process ID
<area-id> : area ID of transit area
<router-id> : Router ID of the router on the other side of the virtual-link
Virtual-link is configured between two ABRs. The area to which the ABRs of the endpoints of the virtual-link commonly belong is the transit area. Note that when configuring virtual-link, the router ID, not the IP address of the router on the other side, is specified.
Please also see the following article about the use of virtual-link.
The following commands are the main show commands for verifying virtual-link.
|show ip ospf interface [brief]||Displays the interfaces with OSPF enabled.|
|show ip ospf virtual-links||Displays the details of virtual-link.|
|show ip ospf neighbor||Displays OSPF neighbors.|
show ip ospf interface
When virtual link is configured, a virtual interface “OSPF_VL<number>” is automatically created. <number> will be assigned in order starting from “0”.
R2#show ip ospf interface brief Interface PID Area IP Address/Mask Cost State Nbrs F/C VL0 1 0 10.23.23.2/24 10 P2P 1/1 Fa0/0 1 0 10.0.12.2/24 10 DR 1/1 Fa0/1 1 23 10.23.23.2/24 10 BDR 1/1 R2#show ip ospf interface OSPF_VL0 is up, line protocol is up Internet Address 10.23.23.2/24, Area 0 Process ID 1, Router ID 22.214.171.124, Network Type VIRTUAL_LINK, Cost: 10 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 2/3, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 1 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 126.96.36.199 (Hello suppressed) Suppress hello for 1 neighbor(s) -- omitted --
show ip ospf virtual-links
Use the show ip ospf virtual-links command to display the details of virtual-links. If it is successful in forming an adjacency with the opposing endpoint router, virtual-link is working properly.
R2#show ip ospf virtual-links Virtual Link OSPF_VL0 to router 188.8.131.52 is up Run as demand circuit DoNotAge LSA allowed. Transit area 23, via interface FastEthernet0/1, Cost of using 10 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:06 Adjacency State FULL (Hello suppressed) Index 2/3, 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
show ip ospf neighbor
Look at the show ip ospf neighbor command, and if it is in the FULL state with the opposite router on the virtual OSPF interface “OSPF_VL”, it is OK.
R2#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 184.108.40.206 0 FULL/ - - 10.23.23.3 OSPF_VL0 220.127.116.11 1 FULL/BDR 00:00:33 10.0.12.1 FastEthernet0/0 18.104.22.168 1 FULL/DR 00:00:30 10.23.23.3 FastEthernet0/1
The following articles are examples of configuring OSPF virtual links on Cisco routers.
- OSPF Overview
- OSPF process flow
- OSPF Router ID : Identify OSPF routers
- What if the router ID of the OSPF router is duplicated?
- OSPF Neighbor and Adjacency
- OSPF DR/BDR
- How show ip ospf neighbor looks on Ethernet
- OSPF Network Type : Classification of OSPF-enabled interfaces
- Synchronization process of OSPF LSDB
- Problems with large-scale OSPF network
- OSPF Area – Inside the area, in detail; outside the area, just a summary
- OSPF Router Type
- OSPF LSA Type
- OSPF Area Type
- OSPF Basic Configuration and Verification Commands
- Details of enabling OSPF on the interface
- OSPF Advertising Loopback Interface
- Configuring and Verifying OSPF Hello/Dead interval
- OSPF Cost Configuration and Verification
- Configuring and Verifying OSPF Router Priority
- Configuring OSPF Neighbor Authentication
- Neighbor Authentication over Virtual-link
- OSPF Configuring and Verifying Stub area [Cisco]
- OSPF Stub Area Configuration Example [Cisco]
- OSPF default route generation : default-information originate command
- Configuration Example of OSPF default route generation : stub area
- OSPF Virtual-Link : Virtual area 0 point-to-point link
- Configuring and Verifying OSPF Virtual-link [Cisco]
- OSPF Virtual-link Configuration Example [Cisco]
- OSPF Virtual-link for discontinuous backbone configuration example
- OSPF Route Summary and Configuration
- Cisco OSPF Route Summary Configuration Example
- OSPF Route Type Preference
- Why the OSPF neighbor state gets stuck in Exstart?
- OSPF packet type and header format
- OSPF Hello Packet
- OSPF DD(Database Description) Packet
- OSPF LSR(Link State Request) Packet
- OSPF LSU(Link State Update) Packet
- OSPF LSAck(Link State Acknowledgement) Packet
- Limitation of OSPF redistribution routes – redistribute maximum-prefix command
- Overview of LSA Filters for OSPF – Filter LSA Type 3/Type 5
- Configuration example of LSA type 3 filter
- Configuration example of LSA type 5 filter
- OSPFv3 Configuration Example [Cisco]
- Configuration Example of OSPFv3 Route Summary [Cisco]