From: Adhu Ajit (adhu_ajit@yahoo.com)
Date: Tue Oct 31 2006 - 02:43:19 ART
Alexei, may be we both are saying the same thing. But here is my opinion.
Narbik sent me an exercise that helped me clarify this option. This is how it works. Let's say a router has 6 indivdual routes and it builds a summary with all these 6 routes. The net route will inherit the properties of all these individual routes that form the aggregate. However, let's say you wish to build the same aggregate using only 4 of those routes and not 6. The advertise-map option can be used to specify the selection criteria for these 4 routes in question.
Thanks,
Adhu.
Alexei Monastyrnyi <alexeim@orcsoftware.com> wrote:
I was completely wrong here.
advertise-map is used to conditionally advertise a summary if a route
matched by this route-map exists.
Tried that in lab and no communities are inherited by summary when using
advertise-map. Must have got confused.
Sorry for the mess.
A.
Alexei Monastyrnyi wrote:
> Hi.
>
> I think it works like this.
>
> If you have a number of routes with long prefix, say /24, and want to
> build /23 or shorter summary out of this set of routes, without
> advertise-map all /24 route attributes will be participating in
> forming a cumulative attribute list for the summary. If you want to
> inherit attributes from particular routes, you pick them with
> advertise-map.
>
> For example some /24 routes have community no-export, you build a
> summary out of all routes and as a result it is going to have
> community no-export. Hence, it is not going to be propagated out of
> your AS even if it was designed to be advertised outside it. Of course
> you can tweak this community explicitly later.. So it is really
> depends on goals, I think, what tool to use.
>
> HTH
> A.
>
> Adhu Ajit wrote:
>> Folks, in the BGP aggregate address command, I do understand how the
>> attribute-map option works. However, I do not quite understand how
>> the option works. Does someone have a config that
>> would explain it to me plain and clear ?
>> Thanks in advance.
>>
>>
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