HSRP and spanning tree

[Steven Williams]

What are some “gotchas” with hsrp and spanning tree? I have read that you should use a layer 3 link between the hsrp routers but I can’t seem to wrap my brain around that. How does that work? Also your active router should have its vlans set for active set to spanning tree priority 0 and its standby vlans for priority 4096

and the opposite for the other hsrp router. How are people designing their networks with with cat9k core switches and nexus switches connecting to them with vpc. Spanning tree can become confusing with all that going on. 

[Seb Rupik]

Hi there,

The Layer3 link between HSRP peers provides a away for packets to be routed to an adjenect router which has aditional routes not available on the active HSRP router. You would need to run a IGP across this Layer3 link.

Again, ensuring that the route bridge for a VLAN is also the active router keeps you STP topology in a optimal state. 

With VPC you still need a FHRP configure as the chassis do not share Layer3 information, so the same STP design decision must be implemented.

cheers,

Seb.

[rishrapsody1]

Important is to make sure we align STP Root and HSRP Primary router or else we will end up with sub optimal path.

L3 link between peers is preferred when there is no need to span vlan across access switches, or to say, when vlan spanning can be avoided

[Steven Williams]

Yes I have made active vlans priority 0 on active hsrp and standby vlans on same device 4096.
then on second peer its active vlans priority 0 and standby ones 4096

[Steven Williams]

what happens when the active becomes the standby though.
That means the standby will be the root for that vlan still.