Configuring OSPF Virtual Links

Use the following commands to configure OSPF virtual links.

Configure a virtual link if the router is a border router that does not have interfaces in the backbone area.

The virtual link is effectively a tunnel across an adjacent non-backbone area whose endpoint must be any of the adjacent area's border routers that has an interface in the backbone area.

Syntax:

set ospf area backbone virtual-link <IP Address> transit-area <OSPF Area>

authtype

md5 key <Authorization Key>

secret <Secret>

off

none

simple <Password>

dead interval {<1-4294967295> | default}

hello-interval {<1-65535> | default}|

{off | on}

retransmit-interval {<1-4294967295> | default}

Parameters:

Parameter	Description
`virtual-link <IP Address>`	Specifies the IP address of the remote endpoint of the virtual link and transit area, which is a specified OSPF area you configure using the "`set ospf area`" command. Configure the OSPF area you are using as the transit area before you configure the virtual link. The transit area is the area shared by the border router on which you configure the virtual link and the router with an interface in the backbone area. Traffic between the endpoints of the virtual link flow through this area. The virtual link IP address functions as the router ID of the remote endpoint of the virtual link.
`authtype md5 key <Authorization Key> secret <Secret>`	Specifies to use MD5 authorization. Enter at least one key ID and its corresponding MD5 secret. If you configure multiple key IDs, the largest key ID is used for authenticating outgoing packets. All keys can be used to authenticate incoming packets. Generally, routers on a given link must agree on the authentication configuration to form neighbor adjacencies. Use an authentication scheme to guarantee that routing information is accepted only from trusted peers. The value "`off`" disables the configured MD5 key.
`authtype none`	Specifies not to use an authentication scheme for the specified interface.
`authtype simple <Password>`	Specifies to use simple authentication for the specified interface. Enter an ASCII string that is 8 characters long. Generally, routers on a given link must agree on the authentication configuration to form neighbor adjacencies. Use an authentication scheme to guarantee that routing information is accepted only from trusted peers.
`dead-interval {<1-4294967295> \| default}`	Specifies the number of seconds after which a router stops receiving hello packets that it declares the neighbor down. Generally, you should set this value at 4 times the value of the hello interval. Do not set the value at 0. For a given link, this value must be the same on all routers or adjacencies do not form. Default: 10 seconds
`hello-interval {<1-65535> \| default}`	Specifies the interval, in seconds, between hello packets that the router sends on the specified interface. For a given link, this value must be the same on all routers or adjacencies do not form. Default: 10 seconds
`{off \| on}`	Disables (`off`) and enables (`on`) the configured OSPF virtual link.
`retransmit-interval {<1-4294967295> \| default}`	Specifies the number of seconds between link state advertisement transmissions for adjacencies belonging to the specified interface. This value also applies to database description and link state request packets. Set this value conservatively, that is, at a significantly higher value than the expected round-trip delay between any two routers on the attached network. Default: 5 seconds