How to remove a BGP route from a summary

[Kevin Brennan]

Hi All,

Is it possible to use a prefix list to remove a specific network from a summary advertisment that was received from a BGP peer?

Example:

I receive 192.168.0.0/22 from an EBGP peer. I want to filter out only 192.168.0.0/24 whilst still allowing 192.168.1.0/24, 192.168.2.0/24 and 192.168.3.0/24.

Can a route map help? Can I remove the summary inbound and replace it with a non-summerised list of routes and then use a prefix list?

Any help would be appreciated.

Thanks

Kevin

[paul driver]

Hello

I assume you are not advetising the aggreegate with the  summary-only commands?
( aggregate-address 192.168.0.0 255.255.240 0 summary-only as-set)

try this: if not using summary-only

access-list 10 permit 192.168.0.0 0.0.0.255

route-map SUP permit 10

match ip access 10

router bgp xx

neigbour xxxx suppress-map SUP

try this: if  using summary-only

access-list 10 deny 192.168.0.0 0.0.0.255

access-list 10- permit any

route-map UNSUP permit 10

match ip access 10

router bgp xx

neigbour xxxx unsuppress-map UNSUP

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[Jose Jara]

Hello Kevin,

Yes, you can use a filter like prefix-list/route-map/distribute-list to filter a specific prefix. I would use a route-map because gives you more flexibility and it is easier to maintain.

In case you are going to generate the aggregate and do not want to advertise a specific prefixes, you could use the methods proposed by Paul, ( except that in the first case the suppress-map is applied with the aggregate command and not with neighbor... ), but I suppose that you just want to deny a specific prefix.

Best Regards,

Jose.

[cadet alain]

Hi,

I don't see how you could filter routes that don't even exist. You only know about the /22 prefix not about the /24s so you can't filter those /24s.

Regards

Alain

Don't forget to rate helpful posts.

[Jose Jara · Accepted solution]

Hi,

I said you could use a filter to deny the specifics of the summary understanding that obviusly you are receiving specific routes of the summary. However, if you are just receiving the summary and not the specifics and you would like to inject specific prefixes from the aggregate, you could do de-aggregation with a BGP feature called Inject-Map. It all depends what are you trying to achieve.

Best Regards,

Jose.

[Kevin Brennan]

Hi All,

Thank you for the assistance. Inject-Map can help me out here.

Regards

Kevin