[c-nsp] BGP conditional advertisemet - NON-EXIST route map's access-list problem

[Dale Shaw]

Hi Burak,

On Mon, Mar 16, 2009 at 12:06 AM, Burak Dikici <bdikici at gmail.com> wrote:
> i am trying to use
> BGP conditional advertisemet configuration. I have got a problem with
> NON-EXIST route map's access-list. In the NON-EXIST router map i am using
> the commands which is written below ;

Here are some notes I made recently when playing with BGP conditional
advertising. I hope it helps.

1.) prefixes matched in advertise-map and exist/non-exist map must exist
(or not) in the *BGP* table
 however: they do not need to be locally originated (e.g. R1 can
match routes received from R2 and advertise (or not) to R3
 and: the validity of the prefix in the BGP table (i.e. RIB-failure)
doesn't matter. if there's there, and using exist-map, the condition
is met.

2.) when using 'exist' map, prefixes matched by advertise-map are
advertised when exist-map condition is met
 example: advertise 1.0.0.0/8 (advertise-map) from BGP table when
3.20.20.0/24 (exist-map) exists in BGP table

3.) when exist 'non-exist' map, prefixes matched by advertise-map are
advertised when non-exist-map condition is met
 example: advertise 1.0.0.0/8 (advertise-map) from BGP table when
3.20.20.0/24 (non-exist-map) does NOT exist in BGP table

4.) prefixes matched in advertise-map are the only prefixes affected --
other prefixes that may exist are advertised (or not) as normal

5.) when dealing with conditional advertisement tasks, always consider
what will happen normally (without any config)

I'd be happy to be corrected, but I think the first point is contrary
to what Ivan said. Also consider point #4 -- BGP conditional
advertising is not strictly a route filtering mechanism, although it
can be configured to achieve similar results.

cheers,
Dale