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How do I configure BGP conditional advertising such that it stops advertising if it loses certain networks?

How do I configure BGP conditional advertising such that it stops advertising if it loses certain networks?

I want BGP to track certain networks learned via an IGP, and if it loses these networks due to an outage or link failure, I want it to stop advertising these networks to its peers.

Given: Networks A, B, and C are learned via an IGP.

Goal: I want BGP to summarize A, B, and C as D, and advertise D to its peers.

Restriction: BGP is to only advertise D if A, B, and C are all present in the routing table. If any one of A, B, or C is missing, BGP should not advertise D. For example, if C is not present, but A and B are, BGP should not advertise D.

I will use the aggregate address command to create D.

However, I am unsure how to create the condition that makes BGP ensure that A, B, and C are present before it advertises D. I am currently researching the advertise map, but I don't know if that will do it.

Does anyone have any pointers or suggestions, or can confirm I am heading in the right direction?

If you use the aggregate command, do you need individual network statements for the networks summarized?

1 REPLY
Anonymous
N/A

Re: How do I configure BGP conditional advertising such that it

Aggregate map or suppress map would not do this for you.

aggregate map just specifies which prefixes are sent as an aggregate while those

excluded are sent as specific routes.

We know that to send an aggregate anyway you need to

distribute igp in bgp and the use the aggregate -address command to

import an agrregate for the igp routes. if you use summary -only is suppresses

the more specific route and send an aggregate instead.

Now to your question, even if one route is missing we would still send an aggregate for the rest

and leave the filtering to be done by the router when it receives a route to the now inactive next-hop.

The only way the aggregate cannot be sent is if there is no igp entry of a route

which you're aggregating i.e no A,b or C.

AS of now i don't think there is a feature that can achive the requested goal. The work around is don't send any aggregate,

advertise only the specific route on as present basic.

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