Multihomed to 2 ISPs - Load Balance?

Mon Jun 26 01:34:18 UTC 2006

Replying to what most of the offline replies that i received said:

>> We wish to load balance the traffic for a block/range of IP addresses
>> that we learn via BGP4 from our two upstream providers. The problem is
>> that my favorite vendor does not let me install ECMP routes in case of
>> routes learnt from extrnal BGP peers. Assuming that we are able to
>> install EBGP ECMP routes, how do we advertise this information to our
>> downstream peers? As far as my working knowledge of BGP4 goes, it wouldnt
>> let me do this.
>> I wish to understand how other network operators do this?

> You don't, not usually anyway.  You advertise the best path to your 
> downstreams.  If you want to 'load balance' per packet or otherwise to one 
> or more upstreams that's an internal/your AS decision only.  There's 
> nothing to tell the downstreams about from BGP's point of view.
>

I think there is a need to tell my downstream peers about ASes the traffic is gonna go through. 

I'm thinking wildly, and it may not make a lot of sense but heres the scenario i have in mind: You load balance (per stream which is usually what most of the vendors do) and you distribute your traffic through ASes 10 and 20. Now you are advertising only one BGP path, say the one through AS 10. Isnt this a problem? Isnt "Advertise what you yourself use" one of the basic shibboleths of BGP or routing for that matter?

Regards,
John

> How exactly you loadbalance the outgoing traffic totally depends on your 
> hardware of choice.

>
> You can, if you wish, send me a message offline and i will collate all
> the information that i receive and send out a consolidated reply for the
> benefit of others to this mailing list.
> Thanks,
> John
>
>
>

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into trouble of all kinds."
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