BGP and Conditionally Advertisement

[smitesh kharecha]

Hi,

Just a quick one...

Do deny statement in prefix-list / access-list works for advertise-map in BGP conditional advertisement ??

I tried a lot of combinations, but it is not working; so just need to confirm is there anything I'm missing.

PS: Talking about the deny statement in prefix-list / Access-list in route-map for Advertise-map and NOT non-exist-map or exist-map.

Regards,

Smitesh

[cadet alain]

Hi,

you need to permit the prefixes you want to conditionnaly advertise.

Regards

Alain

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[paul driver]

Hello,

Are you specifying an condition for the advertised route?

Pleaser post you confg for this conditional route advertisement?

res
paul

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[smitesh kharecha]

Hi Cadet,

Thanks for your feedback; so shall I take that as deny statements in prefix-list /access-list are ignored irrespective of whether it is advertise-map or exist-map or non-exist-map.

Regards,

Smitesh

[paul driver]

Hello

I am not clear on what you are trying to achieve with your deny statements?

If you want to deny or permit a specific route in aggregation, then suppress-map can be used.

The suppress-map logic can use deny/permit acls, with the logic of :
Permit=suprress the route
Deny =not to suppress the route

Advertise-map are to determine what AS path information is retained when performing aggregation on the basis that only if a more specific route of the aggregate is in the bgp table and the as-set option applied.

This can be accomplished by acl or ip as-path acl using permit statements.

res

Paul.

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[smitesh kharecha]

Hi Paul,

Aggregation and suppress-map are not classified as conditional advertisement as far as Cisco DOC goes.

Secondly, Its was not something of production issue, but I was just playing around with BGP in dynnamips ( haven't saved configs ). So where I discovered that

neighbour X.X.X.X advrtise-map ABC exist-map/non-exist-map XYZ

It is documented in cisco DOCs even that deny statement in the prefix-list / access-list in route-map associated with exist-map or non-exist-map ( as per above XYZ )are ignored; however nothing has been said about advertise-map.

When I was playing with the same, I found that any deny statement in prefix-list/ access-list associated with route-map for advertise-map ( as per above ABC ) doesn't have any effect; whatsoever logic you try to implement.

Regards,

Smitesh

[paul driver]

Hello Smitesh -

I mis-understood your use of the advertise-map, I thought it had to do with you performing aggregation, going by your first query -PS: Talking about the deny statement in prefix-list / Access-list in route-map for Advertise-map and NOT non-exist-map or exist-map

So i took this as you didn't want the conditional part of the exist-map or not exist maps to be included, so that's  why I wrongly steered you towards to aggregation and using the suppress-map option.

res

Paul

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[cadet alain]

Hi,

the prefixes to advertise have to be permitted in the prefix-list matched in the advertised-map

Regards

Alain

[smitesh kharecha]

Hi Alain,

Thanks again, so deny statements in prefix-list matched in the advertise-map are ignored ??

Thats what my question is.

Regards,

Smitesh

[cadet alain]

Hi,

they are not advertised, doe that answer your question ?

Regards

Alain

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[smitesh kharecha]

Alain,

Unfortunately, whether the condition ( exist-map or non-exist-map ) is true or false; what I have observered is that prefixes which are denied are always advertised.

Regards,

Smitesh

[Giuseppe Larosa · Accepted solution]

Hello Smitesh,

your test results show that a prefix matching a deny statement in a prefix-list invoked in the advertise-map is NOT processed by the BGP conditional advertisement feature, and so it is always advertised regardless of exist-map or non-exist-map.

This makes sense as the advertise-map should list the IP prefixes to be advertised conditionally depending on the state of the exist-map or non-exist-map.

All IP prefixes not matching the advertise-map are not considered for conditionally advertising including those matching a deny statement in the IP prefix-list invoked within the advertise-map.

Hope to help

Giuseppe

[Bibin Paul]

Hi Smithesh,

If u r using deny statement in prefixlist go for exist map nd if u r using permit prefixlist the go for non exist map

[smitesh kharecha]

Hi Bibin,

You talking about deny statement in prefix-list matched for exist-map / non-exist-map ??

If thats the case, then deny statement matched in exist-map / non-exist-map are ignored.

And if you talking about deny statements in prefix-list matched in advertise-map, do you have any working solution you can present ? Asking as I have tried every possible logics for route-map.

Regards,

Smitesh