3550 BGP routing issue

Unanswered Question
May 6th, 2007
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Hi

I want to know ,does cat 3550 can advertise dynamic routes learned via bgp to another peer or not ?


We have this topology in our network :


3660---- cat3550 ---- 3745----- Internet


Cat 3550 learns the routes from 3660 very well but it does not advertise the learned routes to 3745 ,also it can learns routes from 3745 but it cant advertises routes to 3660 so what should i do if i want my Cat3550 advertises routes to its neighbors.


Any help or configuration guidance will be appreciated.

Thanks.

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mohammedmahmoud Sun, 05/06/2007 - 00:37
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Hi,


If 3660 is running iBGP with the cat3550 and the cat3550 is in turn running iBGP with the 3745, then it would be normal that every iBGP router won't advertise the routes learned from an iBGP router to another iBGP router (iBGP loop prevention mechanism), to over come this problem you'll need to run full mesh iBGP or have a RR (Route Reflector).



HTH, please rate if it does help,

Mohammed Mahmoud.



mrmozaffari Sun, 05/06/2007 - 01:11
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Thanks for your reply ,They are all in same (AS) number ,look the 3660 learn the two dynamic routes from external eigrp and the redistribute it into bgp after this the switch learns the routes but it does not advertise it to next router ,so could you please help me with configuration or something else or refer me to a document ?


Thanks.

mohammedmahmoud Sun, 05/06/2007 - 01:32
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Hi,


Since they are in the same AS they are running iBGP with each other, accordingly they must either be iBGP fully meshed or you have to use a RR (one of them can act as the RR - but in your case since they are just 3 routers, then the full mesh would be ok), any way can you attach the configuration of the 3 routers ?



HTH, please do rate all helpful replies,

Mohammed Mahmoud.

sandow Mon, 05/07/2007 - 05:22
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Be sure the 3550 has "no synchronization" in the bgp config unless you are running an IGP and have all BGP routes injected into the IGP. Otherwise the 3550 will not advertise the routes.


Also helpful to use "next hop self" when configuring iBGP peers in non-fully meshed networks. 3745 will not install routes advertised by 3550 if it does not have a valid route to the 3660, which will be the next hop in the advertisements from the 3550 to the 3745 by default.

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