OSPF and Loopback Interfaces

[kfarrington]

Hello all,

Can anyone tell me why OSPF treats loopback interfaces in it's updates as /32s.

Many thx

Ken

[mazhar71]

Hi,

RFC 2328 says

"

If the state of the interface is Loopback, add a Type 3 link (stub network) as long as this is not an interface to an unnumbered point-to-point network. The Link ID should be set to the IP interface address, the Link Data set to the mask 0xffffffff (indicating a host route), and the cost set to 0.

"

Regards

[ruwhite]

Essentially, because it's a "virtual interface." In fact, with Cisco IOS, you can put the command "ip ospf network-type point-to-point" under the loopback interface, and it will be advertised as with the mask you have configured.

Russ.W