OSPF Summarization

[abbas.ali]

Is it possible to summarize networks 192.100.10.0/24, 192.100.11.0/24, and 192.100.12.0/24?

I redistribute these routes into ospf as connected routes on R1. R2 sees these three routes as E2 in routing table.

I then summarized these three networks into OSPF routing protocol on R1, and hoping that R2 will pick those up. I tried all the combinations, but not luck.

By mathemically , I came up with 192.100.8.0/22, but R2 still shows two E2 routes, one as 192.100.8.0/22 and the second one as 192.100.12.0/24.\

How in the World it would be possible to summarize these three networks as one network, but with /24 prefix not /22?

Any method,

[mehmoodsajid]

yes you can do this with

summary-address

on ASBR

[Georg Pauwen]

Hello,

I have come up with 192.100.8.0/21, see and try if that works.

[rjackson]

Your summary mask should be /21 not /22. /22 includes the "4" bit that makes up 12.

00001100=12

The 22 bit mask with .8.0 includes the bit that makes 12 but requires it to be 0 so .12. shows up as a separate route

.

[abbas.ali]

Thanks everyone. I will try with /21 prefix tonight. Other question was that there is no otherway of summarizing these three routes as a one route with /24 prefix, not /21.

Thanks

[mehmoodsajid]

no there is no way without summarizing

if you want with /24 then you can

summary-address 192.168.x.0 255.255.255.0

but its not good way you know draw backs

only the way is

R1(config)#router ospf 1

R1(router-config)#red static

R1(router-config)#summary-address 192.168.x.x 255.255.248.0

Regards,

Mehmood Sajid

[abbas.ali]

Thanks Mehmood, but I already tried this option:

summar-address 192.168.10.0 255.255.255.0, but it didn't get summarized with just one address such as 192.168.10.0/24. on R2, all three routes 192.168.10.0/24, 192.168.11.0/24, and 192.168.12.0/24 apperared regardless of using the summar-address command on R1.

I guess the only way to summarize with 192.168.8.0/21.