5406-XR1(ospf)# area 50 range 125.100.50.0/21 - range: Unable to create

[James_Levit]

Hi,

I am trying to summarize (aggregate) the following 3 subnets in a multi area ospf config:

125.100.50.X

125.100.51.X

125.100.52.X

I counted the bits and come up with 21 and use the area range command in the subject.  It doesn't take with the error in the subject:

5406-XR1(ospf)# area 50 range 125.100.50.0/21

range: Unable to create

I have to use 5406-XR1(ospf)# area 50 range 125.100.50.0/23 - it works but it doesn't summarize properly - all I did was reduce from 3 routes to 2. 

(Output from Cisco Core)

show ip route

O IA    125.100.50.0/23 [110/2] via 172.16.1.18, 07:36:57, GigabitEthernet8/5
O IA    125.100.52.0/24 [110/2] via 172.16.1.18, 07:37:24, GigabitEthernet8/5

Any thoughts?

[Fredrik Lönnman · Accepted solution]

You cant use 125.100.50.0/21 as a summary, the network in that case would be 125.100.48.0/21 and cover 125.100.48-55 (there are no CIDR to match exactly your three networks).

[James_Levit]

Ohhh.  I see now.  So, if I were to try to implement more meaningful route aggregation, I would have to re-ip the entire network...over 100 subnets.  Not likely to happen.  I just happened to get lucky on the other 2 routers.

Thank for the feedback.