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eBGP multihop


I'm configuring eBGP multihop between two Cisco routers, between the two routers there is a L3 Switch.  proxy is connected to the L3 switch and we are using WCCP to intercept the traffic between the two routers.

On the L3 switch, I'll configure two static routes to the two BGP peering addresses of the two routers. Is that enough? Does the switch need to know the full routing table?

So let's assume that a user is trying to access Cisco web site, when the packet arrives the switch, what is going to happen? does the switch have to have a route for Cisco web site (default route) or no need?




6 Replies 6

Joseph W. Doherty
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Your configuration just needs to insure that the BGP TCP packets, from both peers, are routed correctly.  From what you describe, a couple of static route statements may do the trick.  (BTW, eBGP multihop, is much like iBGP needing the BGP packets to be routed by transit devices, w/o BGP route info.)

Edit - that is what you meant :)


More or less.  ;)

I might add, if the two peers are directly connected to the L3 switch, and routing is enabled on it, it should route between the connected network without the need for route statements.  Route statements should only be needed, if either peer is not directly connected to the L3 switch.

Oh, and to the OP's user traffic question, there's insufficient information to say as you didn't describe the rest of you topology, i.e. how your eBGP peers are involved.  The WCCP proxy muddles the waters for that (user traffic) too because you also didn't note where the proxy is in the topology.  Again, it shouldn't have anything to do with the eBGP peering session, if it's just a proxy for web traffic.

The two peers are directly connected to the L3 switch and no route is required to bring the BGP up.

The Proxy is connected to the L3 switch, and we are forwarding all the traffic to the Proxy (not only web). Only traffic sourced and destined  to/from the BGP peer IPs are excluded from the proxy forwarding..

If your L3 switch is doing route lookups on the destination IPs then it needs routes for those destination IPs.

See my previous post for details.


Jon Marshall
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You will need the following routes.

When traffic arrives from inside to the BGP router it will do a route lookup for the destination IP and see the other BGP peer as the next hop IP so it then needs to work out how to get to that next hop IP.

I assume you will be adding a static to each BGP router for the peer IP address pointing to the L3 switch as the next hop ?

For the L3 switch you don't need the full routing table but it will have to have a default route pointing to the upstream BGP router because it is doing route lookups on the destination IP.

For return traffic the L3 switch will also need to know all the internal subnets so it can forward the traffic back.


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