Creating an OSPF virtual link

Create a virtual link if the switch does not connect directly to the backbone. The switch can create automatic virtual links or you can perform this procedure to create virtual links manually. Manual virtual links conserve resources and provide specific control over virtual link placement in your OSPF configuration.

Before you begin

The router must be an ABR to create a virtual router interface.
You configure OSPF on a VRF instance the same way you configure the GlobalRouter, except that you must use VRF Router configuration mode and replace ipv6 with ipv6 ospf.

About this task

Virtual linking is similar to backup redundancy. The switch creates a virtual link for vital traffic paths in your OSPF configuration if traffic is interrupted, such as when an interface cable that provides a connection to the backbone (either directly or indirectly) is disconnected from the switch. Automatic virtual linking ensures that a link is created by using another switch.

OSPF routes cannot be learned through an ABR unless it connects to the backbone directly or through a virtual link.

Procedure

Enter OSPF Router Configuration mode:

enable

configure terminal

router ospf
Create a virtual link:

ipv6 area virtual-link {A.B.C.D} {A.B.C.D}
Configure optional parameters for the virtual link if the default values do not meet your requirements:
1. Configure the router dead interval:
  
  ipv6 area virtual-link {A.B.C.D} {A.B.C.D} dead-interval <1-65535>
  
  The default is 60 seconds.
2. Configure the hello interval:
  
  ipv6 area virtual-link {A.B.C.D} {A.B.C.D} hello-interval <1-65535>
  
  The default is 10 seconds.
3. Configure the retransmit interval:
  
  ipv6 area virtual-link {A.B.C.D} {A.B.C.D} retransmit-interval <1-1800>
  
  The default is 5 seconds.
4. Configure the transit delay:
  
  ipv6 area virtual-link {A.B.C.D} {A.B.C.D} transit-delay <1-1800>
  
  The default is 1 second.

Example

Create a virtual link:

Switch:1(config-ospf)#ipv6 area virtual-link 0.0.0.1 2.2.2.2

Configure optional parameters for a virtual link:

Switch:1(config-ospf)#ipv6 area virtual-link 0.0.0.1 4.4.4.4 dead-interval 90 retransmit-interval 10

Variable definitions

Use the data in the following table to use the ipv6 area virtual-link command.


Variable	Value
{A.B.C.D} {A.B.C.D}	Specifies the ID for the transit area that the virtual link traverses and the router ID of the virtual neighbor. Do not use 0.0.0.0 for the transit area.
dead-interval `<1-65535>`	Specifies the number of seconds after which the neighbor declares the router down if it does not receive hello packets. Configure this value as a multiple of the hello interval. You must configure the same value on the virtual neighbor. The default is 60 seconds.
hello-interval `<1-65535>`	Specifies the number of seconds between hello packets that the router sends on this interface. Configure the same value on the virtual neighbor. The default is 10 seconds.
retransmit-interval `<1-1800>`	Specifies the number of seconds between link-state advertisement retransmissions for adjacencies that belong to this interface. This value also applies to the retransmissions of database description and link-state request packets. The default is 5 seconds.
transit-delay `<1-1800>`	Specifies the estimated number of seconds to transmit a link-state update packet over this interface. The default is 1 second.