Unanswered Question
Sep 26th, 2007
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I have seen many posts on people with 6500's looking for some layer 3 redundancy and using either HSRP and separating the VLANs between the devices or using GLBP...

I have two 6500's and currently have it setup using GLBP. Should I be using HSRP instead? Is there any reason why I would use GLBP or HSRP over another? Seeing as you can set both up practically the same way why would I use one over the other?

Just a note, if I have half of the VLANs on one and half on the other the "one stays dormant" arguement is off the table. I guess this is a question for the experts!

I also have two FWSM's, one in each device, which I hope to run in active/active mode... This may complicate the answer...

Thanks in advance for your comments!


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IanTarasevitsch1995 Wed, 09/26/2007 - 11:12
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The biggest difference is that GLBP will distribute traffic over multiple routers simultaneously, while HSRP will only push traffic over one active router at a time. If you are running multiple VLANs and are able to group them so that HSRP spreads your traffic load well, then it may not be much of an issue.

Also, keep in mind that HSRP is available on almost all Layer 3 platforms, while GLBP is limited to routers and a small subset of Catalyst switches.

We were running a GLBP network built on two Cisco 3745 routers with 36-port switch modules. The routers did not handle the aggregate LAN load we put on them well, so we installed a pair of Catalyst 3750G's to handle the in-house switching and routing. The CPU utilization is *much* lower, but the 3750s cannot run GLBP, so we had to go back to HSRP.

Also, BTW, we did see an intermittent problem with GLBP. One of our routers crashed, and when we brought it back up, it would cause a broadcast storm every time is tried to re-initialize GLBP. We eventually turned GLBP off and installed the switches instead. Your mileage may vary. Hope this helps!



Joseph W. Doherty Wed, 09/26/2007 - 16:40
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The major difference, GLBP attempts to split the load across a single subnet. This usually results in better load balancing even when there are multiple subnets going to the same routers.

The major caution of GLBP deals with issues of asymmetric path flows.


Ian's mention of 3750 not supporting GLBP is correct, but since you can make a redundant stack, there no real need for GLBP.


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