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Beginner

Default Action for Route Maps applied to BGP

Can some one explain to me the expected default action on a route map like this:

router bgp 64516

neighbour x.x.x.x route-map Prepend out

route-map Prepend permit 10

match ip address ACL (10.0.0.0/24)

set as-path prepend 64516

What i found today is that all other networks weren't be advertised

I had to change my config to

router bgp 64516

neighbour x.x.x.x route-map Prepend out

route-map Prepend permit 10

match ip address ACL (10.0.0.0/24)

set as-path prepend 64516

route-map Prepend permit 20

Then the other networks were advertised correctly.

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Hall of Fame Master

Hello Martin,

the way in which route-maps have to be terminated depends on their use:

route-maps used for PBR do not need a last empty clause because the implicit action in this case is normal destination based routing

A route-map used on a BGP session both inbound or outbound is a route filter that decides what routes can be advertised/received to/from the neighbor and allows also to perform some BGP attributes manipulation.

In this case a last empty clause matching anything else is needed if all other routes have to be advertised/received,  because otherwise the filtering action blocks all routes not matching the previous route-map clauses.

So your findings are correct and the way we terminate a route-map is a key point to be taken in account.

Also route-maps used for redistribution are route filters and have to be terminated accordingly.

Hope to help

Giuseppe

View solution in original post

2 REPLIES 2
Highlighted
Hall of Fame Master

Hello Martin,

the way in which route-maps have to be terminated depends on their use:

route-maps used for PBR do not need a last empty clause because the implicit action in this case is normal destination based routing

A route-map used on a BGP session both inbound or outbound is a route filter that decides what routes can be advertised/received to/from the neighbor and allows also to perform some BGP attributes manipulation.

In this case a last empty clause matching anything else is needed if all other routes have to be advertised/received,  because otherwise the filtering action blocks all routes not matching the previous route-map clauses.

So your findings are correct and the way we terminate a route-map is a key point to be taken in account.

Also route-maps used for redistribution are route filters and have to be terminated accordingly.

Hope to help

Giuseppe

View solution in original post

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Martin ,

You just need to remember the route-map logic i-e

The route-map command includes an implied deny all clause at the end; to configure a permit all, use the route-map command, with a permit action, but without a match command.

Hope this helps you.

Regards.