BGP 2 Sites /19 Routes - more specific routing?

Unanswered Question
Jun 18th, 2008
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Hello!


We have 2 sites with 7500 Routers and BGP


We own a /19 Network

Our Upstream Provider wants me now for load reduction to accept 2 times the same network 1.2.3.4/19 on both sites.


I should then enter the "real" networks on the routers via "more specific" routes.


1 want 1 /24 network to terminate on site 1 the rest on site 2


I have no idea what my upstream provider means..

http://www.cisco.com/en/US/docs/ios/12_0/np1/configuration/guide/1cbgp.html#wp8238


thanks!

marco

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shivlu jain Wed, 06/18/2008 - 00:09
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It's often useful to conditionally advertise some routes to upstream neighbors-

particularly if you are trying to control which link is crossed by traffic destined to a

particular network.BGP has the capability to conditionally advertise routes;

As per me you can use if the one link down automatically the /24 will be announced by the second pair. For this you can use the given command


neighbor x.x.x.x advertise-map toadvertise non-exist-map ifnotexist


access-list 10 permit 172.28.23.0 0.0.0.255


access-list 10 permit 172.28.23.0 0.0.0.255

access-list 20 deny 10.1.3.0 0.0.0.255

access-list 20 permit any

access-list 30 permit 10.1.3.0 0.0.0.255

….

route-map ifnotexist permit 10

match ip address 30

!

route-map ifnotexist deny 20

!

route-map toadvertise permit 10

match ip address 10


regards

shivlu

kmmehlkmmehl Wed, 06/18/2008 - 00:35
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so i can advertise my /24er routes upstream so only the nets i want will terminate on sitea and siteb?



shivlu jain Wed, 06/18/2008 - 00:44
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you can advertise the /24 by one end and with the conf given the seocnd link will chk will the first goes down then it willl be advertise bty the other end.


regards

shivlu

kmmehlkmmehl Wed, 06/18/2008 - 04:49
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Well i dont want a fallback.. it should be only static.


:-)

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