Solved: HSRP vs STP

dasmith58 · ‎06-12-2009

I have 2 X 6513's HSRP'ed as my core switches and have about 50 VLANS. I have the vlan interfaces configured with standby priorities set trying to alternate the HSRP "active" interface in an attempt to load balance between the two switches. I then configured "spanning tree vlan ## root and secondary" on each core without taking into consideration which one was "active" in HSRP. Although I've seen no impact, does this matter? Does one protocol override the the other?

Thanks

cisco_lad2004 · ‎06-12-2009

Does each VLAN terminates as an SVI with its own HSRP group ?

you can always have more HSRP groups, matching STP roots.

So VLAN 2-10 with RTR-A as root with A as Active, and VLAN 11-20 with RTR-B as root and Active.

Sam

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cisco_lad2004 · ‎06-12-2009

No, it should not.

Personally, I would ensure HSRP active is same as root...this will make things more predictable.

(Both technologies serve different purposes and can co exist).

HTH

Sam

dasmith58 · ‎06-12-2009

After discovering my error, I planned to mirror the two (active and root). Keeping in mind I'm looking to try and load balance between my two core switches, any suggestions on which protocol to change?

cisco_lad2004 · ‎06-12-2009

Does each VLAN terminates as an SVI with its own HSRP group ?

you can always have more HSRP groups, matching STP roots.

So VLAN 2-10 with RTR-A as root with A as Active, and VLAN 11-20 with RTR-B as root and Active.

Sam

Jon Marshall · ‎06-12-2009

David

"Although I've seen no impact, does this matter?"

No but it does mean that the link between your 2 core switches assuming it is a L2 link will get used quite a bit more as traffic first goes to the STP root then across to the active HSRP gateway.

Common setup is to mirror the STP root/HSRP active gateway. We used to do odd vlans to one switch and even vlans to another but any system will do.

Jon

dasmith58 · ‎06-12-2009

I figured the Port Channel between the two was being impacted. Unfortunately the guy before me was kind of odd and numbered all the vlans with odd numbers. After viewing "show standby brief" it looks like it will be easier to just change my spanning-tree vlan statements.

Thanks for the assist!

mlund · ‎06-14-2009

Hi

I also recomend you to set the "mac aging time" and the "arp timeout" to the same value, to avoid unicast flooding.

Read this for details of unicast flooding.

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094afd.shtml#t8

/Mikael