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Friday, February 26, 2010

PBR for HTTP traffic with BGP


How can you force http traffic from behind LAN_RTA's Fa0/0 interface to use RT1's link to RT3 to reach web server 10.10.1.10 using BGP's weight attribute? If we then wanted to set the local-preference value in the route map instead of the weight attribute (if there were multiple routers connected to 10.1.1.0/24 for instance) to force traffic from multiple routers to prefer the same path, would we then just need to modify the route-map to set the local-preference to, say 150? How can we then test to make sure that traffic is preferring this path?

You can increase weight for some BGP routes or for all BGP routes received from a BGP neighbor.

neigh 1.1.1.1 weight 5000

or you can use a route-map to increase selectively weight only for some routes.

PBR acts on user traffic packets and it is totally unrelated from BGP. With BGP you can make use of local preference in an AS, for example AS 65001, to select an exit point towards an IP Prefix. BGP as a routing protocol acts on IP prefixes or subnets and does not handle different type of traffic.

If it is acceptable for you to route all traffic with destination A via the same exit point, regardless of traffic type (http but also FTP, telnet and whatever application can be in use) the use of local preference on border router is a possible solution.

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