Solved: OSPF interArea: why advertise /32 prefixes?

Wassim Aouadi · ‎01-31-2009

Hi,

I have 2 routers R2 and R3 in a point-to-point serial connection. OSPF is configured.

R2 is getting interArea routes forwarded by R3. I still don't know why R2 gets /32 prefixes these routes.

example on R2:

" 192.168.9.0/32 is subnetted, 1 subnets

O IA 192.168.9.1 [110/65] via 172.16.23.3, 00:01:09, Serial0/1 "

although the subnets are configured with /24 prefix.

Any ideas? and how to advertise the correct subnet mask?

Giuseppe Larosa · ‎01-31-2009

Hello Wassim,

if the ip subnet is associated to a loopback interface to have OSPF to advertise the right mask you need:

int loop M

ip ospf network point-to-point

otherwise OSPF will advertise a /32 for a loopback ip address

Hope to help

Giuseppe

Giuseppe Larosa · ‎01-31-2009

Hello Wassim,

if the ip subnet is associated to a loopback interface to have OSPF to advertise the right mask you need:

int loop M

ip ospf network point-to-point

otherwise OSPF will advertise a /32 for a loopback ip address

Hope to help

Giuseppe

royalblues · ‎01-31-2009

I assume 192.168.9.1 is a loopback interface on R3

OSPF by default will advertise the loopbacks as a /32 subnet. Inorder to advertise it as a /24 you need to define the interface as point-to-point

interface loop 1

ip add 192.168.9.1 255.255.255.0

ip ospf network point-to-point

Narayan