BPDU detection

[Antonio_1_2]

Hello,

I need to prove that BPDUs, are exchangeed between my two switches.

Here is the situatuion:

SWITCH 1 port 1 ------ PROVIDER1 NETWORK -------port 1 SWITCH 2

SWITCH 1 port 2 ------ PROVIDER2 NETWORK -------port 2 SWITCH 2

Problem is that I have a loop when switch 1 and switch 2 are interconnected via two different providers. I suspect that one of  providers do not propagate BPDUs, or drop some of BPDUs.

1) with "show spanning-tree interface fastethernet 0/1 detail" I can see BPDU sent and received on interface 0/1. Are those BPDU counters refered only to configuration BPDUs? Configuration BPDUs only flow from root toward downstream switches, is that correct?

2)  (SWITCH1) show spanning-tree int fa0/1 detail

Port 9 (FastEthernet0/1) of MST00 is designated forwarding

    ..................................

     BPDU: sent 40, received 0

if SWITCH 1 sends 40 BPDUs, other side SWITCH2 should have in output BPDU received 40, is that correct?

If there is only 30 BPDUs , then some of them are probably droped, is this correct?

3) I tried to use debbuging with debug spanning-tree bpdu, but it seems that this doesn't print out all sending or receiving BPDUs.

Is there any other debbug command that is usefull?

4) are "Hello BPDUs" exchanged on one link even if one of ports is blocked? Is there a way to see those BPDUs (via show command or debug)?

thanks,

A

[Edison Ortiz · Accepted solution]

1) with "show spanning-tree interface fastethernet 0/1 detail" I can see BPDU sent and received on interface 0/1. Are those BPDU counters refered only to configuration BPDUs? Configuration BPDUs only flow from root toward downstream switches, is that correct?

BPDU contain a lot of information. That information is explained on this link:

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/guide/spantree.html

BPDU contains the following minimal information:

•The unique bridge ID of the network device that the transmitting network device believes to be the root bridge

•The STP path cost to the root

•The bridge ID of the transmitting bridge

•Message age

•The identifier of the transmitting port

•Values for the hello, forward delay, and max-age protocol timers

2)  (SWITCH1) show spanning-tree int fa0/1 detail

Port 9 (FastEthernet0/1) of MST00 is designated forwarding

    ..................................

     BPDU: sent 40, received 0

if SWITCH 1 sends 40 BPDUs, other side SWITCH2 should have in output BPDU received 40, is that correct?

If there is only 30 BPDUs , then some of them are probably droped, is this correct?

If Switch 1 sent 40 BPDUs, Switch 2 must have 40 BPDUs received. If that's not the case, the provider is dropping L2 traffic.

3) I tried to use debbuging with debug spanning-tree bpdu, but it seems that this doesn't print out all sending or receiving BPDUs.

Is there any other debbug command that is usefull?

You can SPAN the port to a monitor station and capture all data entering and exiting the switchport.

4) are "Hello BPDUs" exchanged on one link even if one of ports is blocked? Is there a way to see those BPDUs (via show command or debug)?

During the STP learning process, you may see BDPUs exchange. After the STP has converged and the switchport is blocked, no BPDUs will be seen from the leaf towards the root.

Regards

Edison.