BGP Aggregate AS-SET

[lagapidis (Lazarus Agapidis)]

Hello David

@davidilles

If I create a summary route which includes both of the 172.16.x.x networks like this

We can see that the AS Path information has been lost.

Yes, this is to be expected as you suggest.

@davidilles

But if I create a summary route which will only include R3’s 172.16.3.3/32 network

The AS Path information is retained??

In this case it is retained, because you are using the as-set keyword. And since the route contained within the summary comes from a single eBGP peer, it has a single AS path and not multiple ones as shown in the lesson with the curly brackets or braces “{ }”.

I’m not quite sure where your concern is. The only thing that I find strange in the output of your BGP table is the existence of AS number 8, which I don’t see in the topology.

@davidilles

In my first example, why doesn’t BGP just set the AS Path to “2, 1” since those have the networks that we are summarizing, why does it completley remove the AS Path information?

In the first example, the as-set keyword was not used, and that is why the AS path information was removed.

If I have misunderstood your query, please clarify and let me know.

I hope this has been helpful!

Laz