GLBP - Weighting based on bandwidth for one PPP of many?

[mike.welker]

Hi all,

I have two routers at our core data center, a 3845 and a 3640.  These are configured with GLBP.  There are 4 remote sites:

Site #1: One T1 link to the 3825

Site #2: One T1 link to the 3825, and One T1 link to the 3640

Site #3: One T1 link to the 3825, and One T1 link to the 3640

Site #4: One fractional T1 link to the 3825, and One T1 link to the 3640.

My question regards site #4.  If i understand correctly, GLBP works on the premise of "host" balancing, and not true "load" balancing.  The reason I ask is that the large majority of our WAN traffic is from our Exchange server to our remote sites.  In the case of site #4, our exchange server is sending traffic on the fractional T1.  Is there any way with GLBP to either split this traffic from a particular host across two links in a round-robin fashion, but leave other hosts to travel wherever the router sends them, or, to force at least our exchange server to use the full T1, rather than the fractional?

I've read up on the weighting mechanism, and it appears that tracking an interface has nothing to do with bandwidth use.  If I understand correctly, if I were to track the Site #4 PPP to the 3640, and give a weight of 10 to glbp on there, it would really only take affect if the interface is down.  It will have nothing to do with host AVF election.

For the record, exchange traffic is constant to this site, so there is no chance for the host connection to reset and potentially elect to use the larger pipe.

Any thoughts?  It's not a problem necessarily, but I would like to "tweak" this to make better use of available bandwidth.

[marhosenica]

Hello,

I think it's not possible split trafffic from 1 host to 2 links via GLBP. But if you want only true "load" balancing, you can use PPP protocol with Multilink feature. This feature will join two links to one logical and all traffic will bee divided in equal 2 half. This is not GLBP solution, but I hope that can help.

Best Regards, Martin

[mike.welker]

So, now we are presented with a new problem.  We have configured GLBP at site#4 between two 2911 routers, and moved the full T1 over to the new 2911 (One was existing already).

Now ALL traffic is using the full T1.  The fractional is completley unused, except for the periodic eigrp updates between the WAN routers. 

The fractional T1 has a bandwidth statement of 1024 on the remote site router.  Per Cisco, we;ve removed this statement, and we saw all TRANSMIT traffic now using the fractional link, and all RECIEVE traffic to the remote site using the full T1/ new router.

This is odd behavior.  The new router's routing table shows that the learned routes to the core network (an other WAN networks) go through the original 2911. 

We've since rolled back the bandwidth statement removal.  I was under the understanding that GLBP would use host round-robin, regardless of available bandwidth if there were multiple paths, but this behavior is contradictory to that.

Has anyone experienced this behavior with two asynchronous links?