Re: BGP load balancing question

Hi Aaron,

It would be nice if you could provide more information about your
topology. But from what i gather, in your AS, you have 2 border
routers connected to 2 different ISPs and you'd like to load balance
inbound and outbound traffic.

I've thought about the scenario and i personally don't think it would
be possible to load balance outgoing traffic via bgp through any
manipulation of attributes as bgp always installs only one best route
to the ip routing table. Also, load balancing of inbound traffic from
two different ISPs in a real world implementation seems impossible as
both ISPs would be separated by multiple Autonomous Systems.

If you have a solution to implementing such a scenario, i would
appreciate if you shared such information. I'm also studying for my
ccie lab and my opinion might not be the correct one. Thanks.

Ifepe Okwudili.

On 1/22/11, Aaron <aaron1_at_gvtc.com> wrote:
> Equal cost 0/0 routing would seem to be sufficient for influencing outbound
> traffic.... I believe accomplished with underlying Cef switching mechanism
> (src/dst pair hash).... I think u just gotta get the dynamically learned 0/0
> route into your igp... Would seem to save resources (bwidth/mem/CPU) too
> since you only maintain one route from SP.... that's outbound.... Perhaps
> someone else can tackle inbound.... Been a while since I had my dual oc3s to
> att and sprint .... Now I just have dual oc48s to single SP (att) less
> challenging I think with one ISP....can speak to that if you wish
>
> Aaron
>
> On Jan 22, 2011, at 10:30 AM, istong_at_stong.org wrote:
>
>> Hi,
>>
>> I have a scenario I'm looking at and wondering if anyone is
>> aware of any gotchas. I have two different ISP'sconencted
>> to two different boarder routers. The inside network
>> connects to the two border routers via BGP and learns
>> defaults routes from the routers (outbound traffic points to
>> the boarder routers via load balanced default routes). I'm
>> thinking about ways to get the traffic to load balance on
>> the wan links in and out.
>>
>> One thought is to have full routes sent to the border
>> routers and advertise internal routes out both border
>> routers to the ISP's. Then connect the border routers via
>> iBGP and exchange all routes. Lastly I would implement an
>> outbound as-path filter to only permit ^$ (to prevent
>> transit traffic).
>>
>> Any problems with the above scenario. I'm labbing it up but
>> hard to test without a lot of routes to simulate the ISP's,
>> etc.
>>
>>
>> Thanks
>>
>>
>>
>>
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Received on Wed Jan 26 2011 - 08:49:14 ART