From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Mon Aug 14 2006 - 16:19:30 ART
The documentation is correct, however badly worded it is. "the
condition is met when the prefix exists in both the advertise map and
the exist map" means that the prefix matched in the exist map must be in
the BGP table, and that the prefix matched in the advertise map must
also be in the BGP table.
They're basically saying that you can't choose an arbitrary
prefix w.x.y.z/len to advertise in the advertise map if you don't
already have it in the BGP table, i.e. this feature is not for prefix
origination but instead just for conditional prefix propagation.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Radoslav Vasilev
> Sent: Monday, August 14, 2006 3:13 AM
> To: ccielab@groupstudy.com
> Subject: BGP Conditional advertisement - exist-map option
>
> Hi Group,
>
> Advice on the following highly appreicated:
>
> <doccd>
> The route map associated with the advertise-map specifies the prefix
that
> will be advertised to the specified neighbor when the condition is
met.
> When
> configuring an exist map, the condition is met when the prefix exists
in
> both the advertise map and the exist map.
> </doccd>
>
> Does the above mean that this feature only allows us to advertise a
prefix
> to peer A only if we receive it from peer B.
> As far I as i get the command reference, I'm not supposed to be able
to
> have
> different prefix in the EXIST map than the one in the ADVERTISE map
(as
> the
> condition won't be met acording to DocCD).
>
> Yet, while labbing this up, I am able to use two distinc prefixes...
> Just worried that it might differ from ios to ios, or is it just
crappy
> documentation?!
>
>
> sh ip bg neighbor x.x.x.x
> [...]
> Condition-map EXIST, Advertise-map ADVERTISE, status: Advertise
>
> Rack1R4#sh route-map ADVERTISE
> route-map ADVERTISE, permit, sequence 10
> Match clauses:
> ip address (access-lists): 51
> Set clauses:
> Policy routing matches: 0 packets, 0 bytes
> Rack1R4#sh route-map EXIST
> route-map EXIST, permit, sequence 10
> Match clauses:
> ip address (access-lists): 50
> Set clauses:
> Policy routing matches: 0 packets, 0 byte
>
> Standard IP access list 50
> 10 permit 10.0.0.0, wildcard bits 0.0.255.255 (28 matches)
> Standard IP access list 51
> 10 permit 10.1.0.0, wildcard bits 0.0.255.255 (20 matches)
>
>
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