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Community Member

OSPF Route Summary

Hi,

I have a range of network addresses that I would like to summarize into area 0.

router ospf 100

log-adjacency-changes

network 10.70.0.0 0.0.255.255 area 70

network 192.168.70.0 0.0.0.3 area 0

network 192.168.70.4 0.0.0.3 area 0

I was thinking I could just summarise the address range saying if you want to get to anything 10.70.0.0 come to me. So I used the command

area 70 range 10.70.0.0 255.255.0.0

My worry here is I learn a lot of routes to 10.0.0.0 networks such as 10.3.0.0, I just want to make sure that my core routers won't send traffic into area 70 when a route to 10.3.0.0 exists.

6 REPLIES
Silver

Re: OSPF Route Summary

If you want to announce the 10.70.0.0/16 to area 0 then you should use the area 0 range 10.70.0.0 255.255.0.0 command instead of area 70.

There is no overlap between the 10.3.0.0/16 and 10.70.0.0/16 anyway the longest match is still true in respect to select which path to use.

Hope it helps.

Krisztian

Cisco Employee

Re: OSPF Route Summary

Kristian,

You need to use the "area 70 range" command when you want to summarize routes from this specific area into area 0. Using "area 0 range" would summarize routes from area 0 rather than to area 0.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
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Cisco México
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Ciudad de México, 06600
México

Re: OSPF Route Summary

10.70.0.0/16 would suppress more specific routes in this range. Any routes such as 10.3.0.0/xx would be advertised as it is and wouldn't be summarized as it doesn't fall within the 'area range' scope you configured on the ABR. You should have no problems with your proposed configuration.

HTH

Sundar

Re: OSPF Route Summary

Yes, as hritter stated the area id used in the area range command identifies the native area of the route(s) that's being summarized. In this case subnets of 10.7.0.0/xx exist in area 70 and are being summarized into area 0.

Gavin,

Another thing to bear in mind is if there are multiple ABRs connecting area 70 you need to configure the 'area range' command on all of them otherwise the more specific subnets will be leaked through another ABR.

HTH

Sundar

Community Member

Re: OSPF Route Summary

Thanks Sundar,

I had been using the area 70 command and tried it again with the area 0 command and found that area 0 does not work, so I just reverted to my orignal configuration.

Thanks for the help.

Note the rating!

Gavin

Silver

Re: OSPF Route Summary

Guys,

Sorry I was wrong. The are x range subnet where x is the originating area of the subnet and not the area where the subnet will be announced.

Krisztian

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