Spanning Tree Root & Active HSRP switch

Unanswered Question
Dec 3rd, 2009

Should the spanning-tree root be the same switch as the active hsrp switch for a vlan.

If so could someone explain why?

Many Thanks

I have this problem too.
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Jon Marshall Thu, 12/03/2009 - 09:36

darrenriley5 wrote:

Should the spanning-tree root be the same switch as the active hsrp switch for a vlan.

If so could someone explain why?

Many Thanks

Darren

That's a bit of a general statement but for a certain design it does make sense to set it up this way. So

DS1/DS2 are 2 distribution layer switches connected together via a L2 trunk.

AS1 is an access-layer switch with end devices connected in on vlan 10.

AS1 has a L2 connection to both DS1 and DS2. So there is a L2 loop in this setup and STP has to block one of the links.

DS1 is the active HSRP for vlan 10 so the clients will send traffic to DS1 if they want to communicate with other devices outside vlan 10. Now if the STP root for vlan 10 is DS2 then traffic has to go from AS1 to DS2 to DS1 via the L2 trunk.

If you make DS1 the STP root then traffic can go straight to DS1 from AS1.

So that's why it makes sense but it's not critical if they don't match, just be aware that the interconnect between DS1 and DS2 will be more utilised if you don't.

Jon

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