Best Design for multiple WAN links

Unanswered Question
Feb 11th, 2009

I'm putting in 3 fast ethernet links between 2 buildings. For redundancy purposes I have 2 switches\routers on either side. 4509R1 ----> 6509C1 and 4509R2 ----> 6509C2. The 6509's are running IOS not CatOS.

2 of the fast Ethernet ports are on the R1-C1 connection and the last is on the R2-C2 pair.

I've considered Etherchannel on the R1-C1 and going layer2 back to C1 and letting C1 & C2 handle GLBP and routing. I'm not sure this is the most efficient design to maximize my bandwidth utilization while maintaining redundancy.

Anyone have any suggestions?

I have this problem too.
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amguirado73 Wed, 02/11/2009 - 01:49


which design do you prefer? a L2 or L3 design?. You could do a Etherchannel with a source-destination IP load balance method and used STP (or better RSTP) for the backup link. If you have several VLANS you could tune de STP configuration to balance several VLAN for each links.

As far I know GLBP is similar to HSRP and the device should be in the same LAN segment. I suppose if you want a L3 design, you should use same routing protocol that let you a weighted path. I think EIGRP let you it. HSRP o GLBP should be use as entry point to each pair C1&C2 or R1&C2.


Joseph W. Doherty Wed, 02/11/2009 - 04:27

If you use GLBP on C1/C2, you might use the weighed option so that twice as many MACs are processed by C1. That will better balance traffic, in proportion to your links' bandwidth.

Reverse direction going to be more difficult, and you did't describe what's on the 6500 side. You'll likely end up with 50/50 split unless you running EIGRP and what to enable unequal cost.

rshum Wed, 02/11/2009 - 06:08

The 6500's are my core switch/routers and have multiple VLAN's on them. I realized GLBP won't really benefit me on that side.

The 4500 side is a DR site for the most part. Most of the traffic will be flowing out from the 6500's to the 4500 side. It's the nature of the applications, mostly replication and back up stuff being pushed to the 4500's.

I guess I'll go with a layer 3 etherchannel for the C1/R1 connection and just let EIGRP's routing load balance per connection for me. I can't think of a better way to utilize my bandwidth.


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