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HSRP Load balancing and CST

I'm thinking about making use of both of our core routers. At this moment one core is the active router for all 30 vlans. I was thinking about making one core the active router for odd vlans and one for the even vlans. Also, making the cores be the spanning tree root bridge for their respective active vlans. This way, both cores would be sharing the load and both links going to them from the data closets will be used. My dilema is this: some of the switches in our enviroment are 3500 XLs. And 3500 XLs don't support pvst, only cst. Will this somehow cause a problem when we try to make both cores share the routing? Some of the 3500s are in the middle of a stack and some are at the end, connected directly to the core. Either way, will there be a problem with spanning tree and or vlans going in and out of these switches? By the way, the rest of our switches, 3650s and 3750s are using either pvst or rspt. I'm in the process of moving them to rspt.

Thanks, Pat.

Cisco Employee

Re: HSRP Load balancing and CST

HSRP is loadbalancing traffic based on Vlan's. Spanning tree methods used has nothing to do with this. It will not have any effect on this.

All you need to be careful is that you divide the traffic coming from these switches wisely instead of load balancing odd and evens.

What I mean is that

if there are 10 switches on Vlan 1 and 2 on Vlan 2 and 6 on vlan 3 HSRP can help load balance even and odd vlan's but it will not be balanced evenly. so you might put Vlan 2 and 2 on 1 core and vlan 1 on the other to make is a little better balanced.



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