CCNP Switch: MST vs HSRP

Hi Everybody,
Sharing a discovery: Ports blocked by MST can interrupt the function of HSRP. I know that sounds obvious, but it wasn't for me at first. Troubleshooting in my lab for why the Standby router was stuck on "unknown" led to this revelation. Just sharing my experience.

Thanks for listening!

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Comments

Heero

Can you be more specific? HSRP just uses IP multicasts to allow the HSRP routers to communicate. If the multicasts don't make it between the HSRP routers on the subnet, you have greater layer 2 issues to deal with that will affect way more than just HSRP.

theodoxa

It sounds like the relevant port(s) was/were in the STP Blocking state, which would prevent HSRP [or anything for that matter] from communicating.

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