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portfast and bpdufilter

AXISHK
AXISHK asked
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What's the difference between portfast and bpdufilter ? They both block the bpdu prevent a loop ?


spanning-tree bpdufilter enable

spanning-tree portfast
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dmdaviesNetwork Systems Engineer

Commented:
BPDUfilter filters BPDUs in both directions, which will actually disable STP on the port.  Bpdu filter prevents inbound and outbound bpdu and will remove the portfast state on a port, if a bpdu is received.  Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in spanning-tree loops.

spanning-tree portfast enables you to bypass the listening, learning states of STP on a trunk or access port, and is intended more for connecting single host devices, if you configure this on a port connecting to another switch you still run the risk of a network loop.

Author

Commented:
" Bpdu filter prevents inbound and outbound bpdu and will remove the portfast state on a port, if a bpdu is received. "

If it is enabled, bpud shouldn't be received as it has been filtered out.  Why a bpud can still be received in the statement ?

Where should we apply bpdufilter ? Tks
Network Systems Engineer
Commented:
Apologies my comment was in the context of "spanning-tree portfast bpdufilter default"  (a global command) which enables bpdu filtering on all ports configured with portfast, the difference here is that when a port then receives a bpdu packet it reverts to behaving like a normal port, essentially removing the portfast functionality from that port.

If you apply the interface specific configuration:- spanning-tree bpdufilter enable, then as you say you will filter all bpdu's - however you need to be certain of your switch topology with this approach as you would run the risk of a loop occurring.
Don JohnstonInstructor
Top Expert 2015
Commented:
Portfast just bypasses the initial listening/learning phase when a port comes up. Portfast does not alter the behavior of BPDUs.

BPDU filter stops sending of BPDUs.

IMO, it is rarely a good idea to use BPDU filter.  It was originally created to solve a problem that simply doesn't exist anymore.

Author

Commented:
Tks