how to tagg STP BPDU frame

[yoram12345]

Hi all,

I have a switch catalyst 3750 which runs spanning tree (MST).

The switch is connected via  gige link to 3rd party equipment that can pass only L2 vlans , but not the RSTP BPDU.

I need a cisco command or configuration in which i could send the BPDU frames Tagged with specific vlan.

I tried to use MST , PVST but when i connected wireshark sniffer to teh gig ports , i noticed only untagged BPDU frames.

Is it possible with catalyzt 3750 ?

BR,

Yoram

[tverhell · Accepted solution]

Correct,

also check following link, how to make sure your PC will capture vlan-tags when using wireshark

http://wiki.wireshark.org/CaptureSetup/VLAN

Tom

[yoram12345]

hi all,

I managed to view the vlan tagg via wireshark after i updated the intel NIC via regeedit commands as appears  in the link you have sent, thanks.

I have anotehr problem that when i connect the wireshark directly ro cisco STP ports i can view the packets , however when i configure the cisco with port mirror and pass the sniffer to the mirrored port but it seems the cisco mirrored port does not pass the frames .

any ideas

[Giuseppe Larosa]

Hello Yoram,

as Tom and Jon have already noted the destination port of the monitor session has to be configured as a trunk port in order to see vlan tags of mirrored traffic.

Please note:

you can easily verify that PVST+ or Rapid STP BPDU frames are carried over the L2 transport service by using

show spanning-tree interface type x/y detail

where type x/y is the Cisco switch interface that acts as L2 CE node

you should be able to see a line called designated bridge ...

if there is communication both Cisco switches will agree on Designated Bridge bridge-id

if there is no communication each sides thinks to be the designated bridge/ DP for the link

This applies to each L2 Vlan permitted over the link

Hope to help

Giuseppe