BGP route selection - need help


My site has implemented BGP, two routers connecting with 2 different ISP (A & B), uneven bandwidth on these two lines, running IBGP between two routers. I'd like to choose ISP A as the primary and ISP B as backup. Which means both inbound & outbound traffic will route thru ISP A. If router A fails, it will fall back to ISP B. Can anyone post the parameter here ?

Much appreciated and thanks.

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How is it routing today? Both are running an IGP back with your core I presume? Which route does the core prefer for As for return traffic, that needs to be coordinated between your ISPs. If it is instead preferring the wrong connection (which would very much surprise me due to the bandwidth differences), then you can use a weight or something similar (depending which IGP you are running: eigrp, ospf, etc) to ensure that one router's is preferred in the core.

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Do your two BGP routers receive a default route from each ISP or a full routing table?

In a nutshell, to get inbound traffic preferred over ISP you would prepend your AS number to ISP B so that the path to you is longer over that ISP and therefore preferred via ISP A (with no prepend).

Outbound depends on how you have implemented BGP. Generally I would tag inbound routes with a local pref (the higher the local pref the more preferred the route) and set a higher local pref for the routes received from the preferred ISP.


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