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bpdu guard on bridge/switch/hub?

Hi,

I would appreciate some comments on the below:

1) is it true that bpdu is sent on bridge or switch. hubs don't send bpdu.

2) when bpdu guard is implemented on a cisco switch with portfast enabled and connected to 3com/HP switches, the port is not shutdown/disabled?

Thanks.

Christina

2 REPLIES
Cisco Employee

Re: bpdu guard on bridge/switch/hub?

Hi Christina,

For #1, that is correct. Hubs do not send BPDUs.

For #2, the expected behavior would be that any port with bpdu guard enabled that receives a BPDU should be shut down. Secondly, a link that is connected to a switch should never be configured with portfast.

HTH,

Bobby

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Re: bpdu guard on bridge/switch/hub?

bpdu's are sent on switches. (basically a smart bridge). bpdu's are not generated by hubs or responded too by hubs.

if a switch that has bpdu guard enabled receives a bpdu via a portFast port, it puts the portFast port into errorDisable mode, effectively stopping all packet forwarding. (this is the guard that keeps the portFast port from allowing the connected switch from taking over as the root bridge)

the best way to prevent this is to configure the 3com/HPswitch from sending bpdu's (raise the bridge priority) or better yet, have it participate in spanningTree (disable portFast for that port; also with a higher bridge priority on the 3com/HP switch)

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