BPDU guard and Root guard on same port

[Andy White]

Hello,

I'm sorting some switches out and it seems many ports have root and BPDU guard enabled on them, but I can't understand why?  Surely if you have BPDU guard enabled it will stop a superior BPDU thus stop STP recalculating paths to a new root bridge?

Thanks

[blau grana]

Hello Andy,

It does not make much sense to have both configured on same switch ports.

BPDU guard - used on edge routers, mostly with portfast, disables port upon receiving BPDU

Root guard - protect your topology against unpredictable root election, used on switch ports toward switches with lower priority [should never become roots]

Just from usage it is clear that configuring both features on same port does not make sense.

Best Regards

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[Andy White]

Good that was what I thought, it confused me when I saw that.  With regards to root guard I normally just set this on the root switch on ports leading to other switches (trunks), what you say that is right?

[InayathUlla Sharieff]

HI Andy,

You got it right. You  need to configure the Root guard on the root switch on ports leading down the tree.

Root guard is best deployed toward ports that connect to switches which should not be the root bridge.

Other way of doing that is:

The Root Guard feature can be enabled on all switch ports in the network off of which the root bridge should not appear (that is, every port that is not a root port , the port on each switch that is considered to be closest to the root

bridge). If a port configured for Root Guard receives a superior BPDU, instead of believing the BPDU, the port goes into a root-inconsistent state. While a port is in the root-inconsistent state, no user data is sent across it. However, after the superior BPDUs stop, the port returns to the forwarding state.

HTH

Regards

Inayath

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