[c-nsp] Conditional advertise-map

[Oliver Boehmer (oboehmer)]

Richard,
 
> I have a scenario where I have two upstreams ASN5511 and ASN36997.
> Both do send me a default route and I choose ASN5511 as the best path.
> All my outbound traffic is via ASN5511 and the return is distributed
> between the two. What I want however is to use an advertise map so I
> ONLY advertise my prefixes to ASN5511 so I only use his link but
> fail-over to advertising my prefixes to ASN36997 in the event ASN5511
> fails.
> 
> I have created the the two route-maps to be matched NO_DEFAULT_FT and
> AS_LIST and configured as below.
> 
> ## access list below is to avoid me feeding back to my up-streams
> the routes learned from other up-streams. That way I only advertise
> to the up-streams only prefixes from me and my down-streams.
> 
> ip as-path access-list 10 deny ^5511_
> ip as-path access-list 10 deny ^12455_
> ip as-path access-list 10 deny ^36997_
> ip as-path access-list 10 permit .*
> !!
>
> ## Match against filter below. If anything from ASN5511 is available,
> 
> ip as-path access-list 20 permit ^5511_
> !!
> 
> route-map NO_DEFAULT_FT permit 10
> match as-path 20
> !!
>
> route-map AS_LIST permit 10
> match as-path 10
> !!
> neighbor 41.222.1.33 advertise-map AS_LIST non-exist-map NO_DEFAULT_FT
> 
> 
> Any ideas why it doesn't work.

I'm not 100% sure, but as far as I was able to find out, you can't use
an AS-path ACL in the non-exist-map (NO_DEFAULT_FT) to match on the
prefixes. The router searches the main routing table (so the match for
routes is not limited to BGP prefixes), which does not include the AS
path information. 

Can you replace this with a prefix list matching on some AS5511
prefixes?

	oli