Hi,
I am implementing BGP in my network. I have a valid AS and my own range of IP adresses. My AS is multihomed to two providers, and I wont be passing traffic to anybody(not a transit AS). I have two routers, each one with the link of one provider, so if one of the routers fails, my network wonīt be unreachable from the Internet. The BGP configuration(route maps, metrics, as prepend, local preference, ...) I know how to do.
To have redundancy for my internal servers/routers, I decided to configure HSRP in the ethernet interface of the routers, and in the preferential router, I also configure the HSRP to monitor the serial interface(link), so if this preferential router or itīs serial link goes down, the other router will assume itīs IP, and the internal servers/routers will route traffic through it automatically.

Both of the routers ethernet interfaces are in the same subnet linked to the same switch. My doubt is:
I pretend to use both of the links when both of them are online, I will achieve it through AS path and local preference manipulation. For some networks the prefered route will be one link, and for others the prefered route will be the other link. But all of the internal servers/machines will have the default gateway configured as the HSRP IP, so all the traffic will be primarily directed to the prefered router, even if the destination is to exit my AS through the other link. So for this traffic, that is supposed to leave my AS trhough the other link, the prefered router will receive the traffic, and then route it to my other BGP router through the SAME interface. Is there any problem in designing the network this way? With one router receiving some traffic and routing it through the same interface? Will there be any performance loss? How could i measure this loss?
My links are both dedicated 2 MB links, and the ethernet are 100MB(fast ethernet), so I suppose that this traffic wont be enough to affect the ethernet traffic right?

My other doubt is:
When the routers are working with HSRP, both in the same logical and phisical network, and the router that is using the HSRP IP receiving all traffic, when this router receives traffic that is to leave my AS through the other router, will the prefered router send ICMP redirects to the internal servers/routers, telling them that the prefered gateway for this traffic is the other router? If yes, is this bad? Will it influence the network in any way? Can I disable it?

Thanks in advance.

Last edited by sf1 on 07-29-03 at 01:57 PM

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You are overlooking one major point. You have no control over return traffic and you are going to find that one ISP is preferred for more than 70% of that return traffic.

Sounds to me like you are trying to over engineer your side of the connection and that usually means trouble.

You could let your border routers each receive the entire internet BGP table from the attached ISP and pass that table back to another router (or two for redundancy) that would determine which provider has the best path to the destination. We also have to connections and puzzled long and hard on how to handle it before deciding on this method.

just me two cents,

Yankee

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Yeah, I know that the best would have another router to decide it, but the fact is that I dont have this third router.
So, I just would like to know if there would be any impact on the prefered router's ethernet interface performance with this design.
You said that I dont have any control over the return traffic, but as far as I know I have control over returning traffic by changing my routes AS paths with route maps(AS prepend). Is this wrong?

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http://www.cisco.com/warp/public/45...oc.html#BGPsec1

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you could also have both your providers send you meds and use always-compare-med.

you have ibgp between the routers right ?

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Yeah, I have iBGP runnnig betwen the routers.
But you guys didn't understand, my doubt is not about BGP, my doubt is with my internal design, with one router receiving some traffic in it's ethernet interface, and routing this traffic to another router via this same ethernet interface. Is there any problem with this?
Thanks very much for your time anyway.

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don't expect anyone to understand your
design unless you provide a better description or diagram of what's going on.
bgp is awesome .....
try reading halabi or parkhurst or look
at the case studies i provided.

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dang I hate agreeing with my old buddy Darth, but as always he is right

Yankee

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Do you mean routing out the same interface a packet came in on? If so I can't see why there would be any issues with that on a purely routning perspective...

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