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HPSwitch & 3Com switch PBDU dismatch.

Senior Member

HPSwitch & 3Com switch PBDU dismatch.



I had a customer, when he connect from Switch HP5500 to 3com4526, the port at 3Com4526 site will auto disable during operation. I check on the log on 3Com switch display as below:


#Apr 24 22:59:46:714 2000 3C4526-L4#2 MSTP/2/LGEXP:- 1 - I am the root of instance 0 now!
%Apr 24 22:59:46:897 2000 3C4526-L4#2 MSTP/3/BPDUFORMATERROR:- 1 -Port GigabitEthernet1/0/28 received different format of BPDU packets continually! Shut down it in order to avoid broadcast
#Apr 24 22:59:47:401 2000 3C4526-L4#2 L2INF/2/PORT LINK STATUS CHANGE:- 1 -
 Trap portIndex is 4227841, ifAdminStatus is 2, ifOperStatus is 2



Both side port been configure it trunk as below:


HP5500 switch:

interface GigabitEthernet1/0/19
 port link-mode bridge
 port link-type trunk
 port trunk permit vlan all
 broadcast-suppression pps 3000
 undo jumboframe enable
 stp edged-port enableinterface


3Com switch:

interface GigabitEthernet1/0/28
 stp edged-port enable
 port link-type trunk
 port trunk permit vlan 1 106 to 107



What does it mean by the log? Could anyone assist me on this matter, thanks.

Honored Contributor

Re: HPSwitch & 3Com switch PBDU dismatch.

It means the 3com doesn't understand the kind of spanning tree protocol the 5500 is using (in the top line of display stp output). This might potentially cause a forwarding loop, and network storm, so it shuts down the port.


You could downgrade the spanning tree protocol to an earlier version (e.g. to RSTP). Or you might get later firmware for the 3com, from ther HP support site.

Senior Member

Re: HPSwitch & 3Com switch PBDU dismatch.

I had found the root cause few month ago and it was a big mistake! That is because the HP5500 switch STP feature don't enable. It was new switch come with no stp enable, i never thought stp is disable by default.


I enable stp then the problem sloved. Thanks for your reply.