From: Dale Shaw (dale.shaw@gmail.com)
Date: Tue Feb 17 2009 - 22:21:38 ARST
Hi,
On Wed, Feb 18, 2009 at 9:23 AM, Mahesh Shivaswamy
<maheshs.cisco@gmail.com> wrote:
> I am not sure why is R2 advertising prefix 136.1.29.0/24 when the
> route 136.1.23.0/24 exist in the routing table ???
Here are my recent notes on BGP conditional advertisement:
bgp conditional advertisement
- 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.
- 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
- 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
- prefixes matched in advertise-map are the only prefixes affected --
other prefixes that may exist are advertised (or not) as normal
- when dealing with conditional advertisement tasks, always consider
what will happen normally (without any config)
I think the first point is probably where you are getting tripped up.
cheers,
Dale
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