RE: BGP - Preventing the AS from advertising local net

Could you show full config of BGP, and the whole prefix list and route-map,
don't cut anything out. Also, is 172.16.0.0/24 a local net that you mention,
or the local net is something else?

When you remove route map, do you see everything back to normal, so it's a
route-map that gives you an issue?

Do you have an empty entry in your route map to permit other networks to
pass, in case the local network is not 172.16.0.0/24? If that's the only
route map entry, then everything that is not matched there will be filtered
out.

Cheers,

Adel Abouchaev, CCIE# 12037, CISSP, MCSE

Technical Support Engineer
Netmasterclass LLC, Cisco Learning Partner
RFC821: adel_at_netmasterclass.net
E.164: +18886772669
HTTP: www.netmasterclass.net

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
ccie_ka_at_gmx.de
Sent: Saturday, April 03, 2010 8:41 AM
To: ccielab_at_groupstudy.com
Subject: BGP - Preventing the AS from advertising local net

Hi GS,

assume there is one AS with the network 172.16.0.0/24
Also there are 2 other AS's

What is the best practice to prevent _only_ this network to advertise to the
BB routers ?

router bgp 33
 neighbor x.x.x.x remote-as 33
 neighbor x.x.x.x send-community both
 neighbor x.x.x.x route-map PREV out

ip prefix-list prevent seq 5 172.16.0.0/24

route-map PREV
 match ip address prefix-list prevent
 set community no-advertise

THis soulution prevent the local net to send to the neighbor..

Right now my problem is I doesn't understand why...;-)
Because I thought the community no-advertise is send to the _next_ AS and
prevent the specific prefix to send outr the neighbor AS ?!?!

Please can anyone explain me if this a normal behaviour...

Thanks

Dennis

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