question about the command spanning-tree portfast bpdufilter default !!

[Dr.X]

hi ,

i just want to ask about the command

case 1

i have  port and i assigned on it portfast feature then from global command i typed  ,

#spanning-tree portfast bpdufilter default

i read about it that every port that has portfast feature will enable the bpdufilter on it  , it just disable the port from spanning tree and dont send or recive bpdu .

but i want to ask ,

if by mistake a bpdy was recived on that port .

what will happen ??

will it go into error disable or it will lose the portfast feature and become as normal port  or it just ignores the bpdu ?

case 2

if i have another switchport interface and i just typed under interface command ,

spanning-tree bpu filter enable

what will happen if this port recive by mistake a bpdu ?

will it go into error disable ?

or

it will become normal stp port ???!!!

or

ignore the bpdus ?

==========================

plz advice in this point i have some confusion

regards

[paul driver · Accepted solution]

Hello,

This one always gets me! - have look at link below from Keith Barker.

BPDU Filter:
###########
If applied to Global config

Stops BPDUs from being sent or received on ports that are operationally using portfast.

BPDUs will trigger the port to stop using portfast, and BPDU filtering will stop on that port.  

If applied in interface config,
BPDUs will be filtered, regardless of portfast operational state protential

Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in spanning-tree loops.

https://learningnetwork.cisco.com/message/153796#153796

res

Paul

Please don't forget to rate this post if it has been helpful.

[Dr.X]

hi paul ,

thanks so much for explanation ,

let me ask you another question ,

what about bpduguard ???

if applied on global config

and

if applied under interface config

wt will happen if recieved bpdu ??

regards

[paul driver · Accepted solution]

Hello,

Bpduguard operates differently depending on what node it is configured.

Global - spanning-tree portfast bpduguard default

Its enabled on portfast enabled ports and stp will shut down the port of bpdu are seen on that port - ( err-disable)

Interface - spanning-tree bpduguard enable

will err-disable the port if bpdu's are seen with or without portfast enabled

res

Paul

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_55_se/configuration/guide/swstpopt.html#wp1095752

Please don't forget to rate this post if it has been helpful.

[Dr.X]

hi paul ,

thanks very much .

you really gave me nice explanation about my confusing points

thanks alot

regards