RE: BGP load balancing question

I labbed it up and then put it in production as it worked well in the lab.
The outcome was as follows:

routerA to ISPA
routerB to ISPB

routerA iBGP peers with routerB

routerA and routerB are fed full BGP routes from their different ISP's

The routers prefer different routes within BGP from each ISP for various
reasons (AS path, egp vs igp, etc, etc. The net affect is about a 60/40
split on both inbound and outbound traffic. That was the desired affect so
that I can use both links from the ISP's, since I was maxing out the link
when just using an active/standby routing solution using AS prepend and
higher local pref on one router versus the other.

The obvious remaining issue is if one link goes down the other will be
overutilized. I'm ordering upgrades for both links to address that failure
scenario :)

Thanks for the input guys,

Ian

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Narbik Kocharians
Sent: Wednesday, January 26, 2011 11:31 AM
To: Okwudili Ifepe
Cc: Aaron; istong_at_stong.org; <ccielab_at_groupstudy.com>
Subject: Re: BGP load balancing question

It is possible to load share for a given prefix or bunch of prefixes
when you have one router connecting to two different ISPs, but here you have
two. Do these border routers connect to both ISPs?

On Tue, Jan 25, 2011 at 11:49 PM, Okwudili Ifepe
<okwudilic2003_at_gmail.com>wrote:

> 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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-- 
*Narbik Kocharians
*CCSI#30832, CCIE# 12410 (R&S, SP, Security)
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