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EDGE Routing to Single ISP

Unanswered Question
Sep 26th, 2013
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Hello All,

We have the following setup

C1 and C2 are Core Routers peering with same ISP through ebgp and ospf peering with D1 and E1. There is no firewall between C's and E but there is active/passive setup between C's and D. Now, let's assume D1 is advertising and networks to C's which is intern advertising in BGP to the world. My understanding is we would announce those  two network statement's and bunch of other networks from E (not 1918) in both the routers C1 and C2 , to better load sharing and redundancy. Will that cause any assymetric routing issues ?  If we do announce on both routers, should we expect load sharing on both the routers as both has a GiG Internet Connectivity  , or should we tweak in with bgp attributes ?




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Lei Tian Fri, 09/27/2013 - 05:13
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  • Cisco Employee,

Hi Josh,

I think your approach is right. Advertise all prefixs from both C1 and C2 to the ISP will give you the redundancy. Asymemtric routing shouldn't be an issue, if that's one FW between C and D. BGP doesnt do load sharing by default, unless ISP agree to config multi-path ebgp, only one path will be installed in the routing table for one prefix. If you want get inbound traffic load balanced acorss C1 and C2, you need to play the bgp attribute or advertise different prefixs on each WAN router. For bgp attribute, you can do as-prepend of the prefixs on the WAN router to make that path less prefer.


Lei Tian


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