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glbp and bgp

 
 
D.Albertson
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      10-27-2003



Anyone have any expierience with GLBP (gateway load balancing proto 12.3
ios) and multihomed bgp?


Lets say for instance


we have 2 ciscos each running bgp with a different upstream
now would it be a bad idea to put GLBP in the mix with the intent
of load balancing out bound traffic across wan links?

Would there be an issue of potentially causing problems with packets
arriving out of order
at the recieving side do to a longer trip for half of the packets


assuming we had one sprint link and one att link and we were sending packets
to a sprint customer
I guess all the packets sent through the sprint pipe would get there before
the ones going through the att pipe.

Maybe some kind of flow cache can be implemented?

I guess I am just wondering if anyone is running a multihomed bgp setup and
GLBP ?

Thanks much!


 
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Mike Gallagher
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      10-28-2003
Well, I'm using GLBP, but not with BGP, but it really doesn't matter.
GLBP has the concept of an Active Virtual Gateway (AVG) and Active
Virtual Forwarders (AVFs). The AVG assigns a virtual mac address to
each member of the GLBP group (including itself). The AVFs are
responsible for forwarding traffic for/responding to their assigned
mac address. The other members of the GLBP group back each other up in
case of failure.

When a host arps for its default gateway (the virtual IP address in
the GLBP group), the AVG responds with a virtual mac address for a
router in the GLBP group. There are several ways to configure this
distribution, check the docs. So, the question is, what is behind
your two routers? A single firewall, a LAN with all your hosts? If a
single firewall, then GLBP really won't do a lot for load distribution
since the firewall will arp once and take that router until it needs
to re-arp. Then it will get the virtual mac of the other router, then
use that one. It's a little better than just using HSRP.

If you have a LAN with all your hosts behind it (same subnet as the
routers), then you'll get good load distribution across the ISPs. You
most likely will have some asymetric routing, but you won't really
have out-of-order packets, because each host is tied to sending data
to a particular router, and in your case, one ISP.

HTH,

Mike

"D.Albertson" <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> Anyone have any expierience with GLBP (gateway load balancing proto 12.3
> ios) and multihomed bgp?
>
>
> Lets say for instance
>
>
> we have 2 ciscos each running bgp with a different upstream
> now would it be a bad idea to put GLBP in the mix with the intent
> of load balancing out bound traffic across wan links?
>
> Would there be an issue of potentially causing problems with packets
> arriving out of order
> at the recieving side do to a longer trip for half of the packets
>
>
> assuming we had one sprint link and one att link and we were sending packets
> to a sprint customer
> I guess all the packets sent through the sprint pipe would get there before
> the ones going through the att pipe.
>
> Maybe some kind of flow cache can be implemented?
>
> I guess I am just wondering if anyone is running a multihomed bgp setup and
> GLBP ?
>
> Thanks much!

 
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