Network Engineering Stack Exchange is a question and answer site for network engineers. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

enter image description here

Here is a simple network using OSPF. Router2 has got LoopBack0 with IP address I add this network to OSPF:

Router(config-router)#net area 0

When I dispaly routing table in Router2 - I see there directly connected. But in Router3 routing table I see is subnetted, 1 subnets

O [110/65] via, 00:00:12, Serial0/0/0

Why there is prefix /32 ?

share|improve this question
up vote 5 down vote accepted

Loopback interfaces are considered as host routes, so they are always advertised with a /32 mask.

If you want to advertise the whole subnet, you have to change the network type to point to point like this:

Interface loopback 0
 ip ospf network point-to-point

then OSPF will advertise the subnet with the configured mask.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.