OSPF interArea: why advertise /32 prefixes?

Answered Question
Jan 31st, 2009
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<p>Hi,<br />

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

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

<br />

example on R2:<br />

"     192.168.9.0/32 is subnetted, 1 subnets<br />

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

<br />

although the subnets are configured with /24 prefix. <br />

Any ideas? and how to advertise the correct subnet mask?</p>

Correct Answer by Giuseppe Larosa about 8 years 4 months ago


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


 

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Correct Answer
Giuseppe Larosa Sat, 01/31/2009 - 02:29
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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 Sat, 01/31/2009 - 02:34
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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

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