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New Member

debugging spanning tree

I am looking into some lan probs and I am using the document:

Troubleshooting Spanning-Tree Protocol and Related Design Considerations

as a resource. In the section:

An Additional CatOS Command

The Catalyst specific software is richer than the IOS as far as STP troubleshooting is concerned. The command show spantree statistics <module#/port#> <vlan#> gives very accurate information on a specific port. On suspected ports, run this command and pay special attention to the fields:

Forward trans count: this counter remembers how many times a port transition from learning to forwarding. In a stable topology, this counter should always show 1. This counter is reset to 0 is the corresponding port is going down and up. So, if the value is higher than 1, it means that the transition this port experienced is the result of a STP recalculation, not of a direct link failure.

Max age expiry count: this counter tracks the number of times the max age expired on this link. Basically, a port expecting BPDUs will wait for max age (default 20 seconds) before considering its designated bridge as lost. Each time this event occurs, the counter is incremented. When the value is not zero, you know that for whatever reason, the designated bridge for this LAN is unstable or has problem transmitting its BPDUs.

I need some clarification.

To utilize the command 'show spantree stats mod/port vlan', should this

be done on the trunk ports AND only for active vlans on the switch?

OR

Should it be done on all ports for all vlans everywhere?

OR should it be don for trunks only for all vlans everywhere?

Secondly, the statement 'Max age expiry count: this counter tracks the number of times the max age expired' seems to be a typo. I can only see a 'msg age expiry count'. Clarification is needed here-is it a typo or did I miss the counter?

Thanks in advance.

8 REPLIES

Re: debugging spanning tree

Hi,

AFAIK, to utilize the command 'show spantree stats mod/port vlan', this should be done on the trunk ports AND only for active vlans.

You can try it on passive (pruned) VLANs - STP is still running, but if there are no user data passing the VLAN, it has not a big sense to check it.

If you try to issue 'show spantree stats mod/port vlanx' and VLANx is disabled on the trunk, you just receive 'Vlan x does not exist' message.

If you try to issue 'show spantree stats mod/port vlanx' on port which is not a trunk, you receive:

SpanningTree enabled for vlan = x

Invalid Port : Not part of dynamic SPT data structure.

To your secon question:

'Max age expiry count' is a typo, 'msg age expiry count' is correct.

See http://www.cisco.com/univercd/cc/td/doc/product/lan/cat4000/7_5/cmd_ref/sh_s_t.htm#1026947 for details.

Regards,

Milan

New Member

Re: debugging spanning tree

Thanks for your help. Along these lines using the 'show spantree

mod/port vlanx' I need some further clarification. The document says

Forward trans count: this counter remembers how many times a port transition from learning to forwarding. In a stable topology, this counter should always show 1. This counter is reset to 0 is the corresponding port is going down and up. So, if the value is higher than 1, it means that the transition this port experienced is the result of a STP recalculation, not of a direct link failure.

I found a link that shows 0, not 1 or not a value higher than 1. Is this a

software bug or does it indicate a problem?

Re: debugging spanning tree

Hi,

it seems like a portfast enabled port.

Portfast is skipping the listening and learning phase so there is no learning to forwarding transition to remember.

Regards,

Milan

New Member

Re: debugging spanning tree

This is the config for the port:

set port channel 1/1-2 321

#module 1 : 2-port 1000BaseX Supervisor

set port trap 1/1-2 enable

set udld disable 1/2

set trunk 1/1 auto isl 1-1005

set port channel 1/1-2 mode off

I don't see anywhere that portfast is enabled. Is there something else

I should check?

Re: debugging spanning tree

Hi,

try sh spantree mod/port.

It should show portfast value directly on the port.

It can be configured via several ways, set spantree global-default portfast ena, e.g.

Another idea (if portfast is not enabled): the 0 value migth be caused by the fact the port has never (since the last switch reload) gone up?

Regards,

Milan

New Member

Re: debugging spanning tree

ac-sw-1> (enable) sh spant 1/1

Port Vlan Port-State Cost Priority Portfast Channel_id

------------------------ ---- ------------- ----- -------- ---------- ----------

1/1 1 forwarding 4 32 disabled 0

1/1 2 forwarding 4 32 disabled 0

1/1 10 forwarding 4 32 disabled 0

1/1 15 forwarding 4 32 disabled 0

1/1 17 forwarding 4 32 disabled 0

1/1 18 forwarding 4 32 disabled 0

1/1 20 forwarding 4 32 disabled 0

1/1 25 forwarding 4 32 disabled 0

1/1 26 forwarding 4 32 disabled 0

1/1 27 forwarding 4 32 disabled 0

1/1 30 forwarding 4 32 disabled 0

1/1 40 forwarding 4 32 disabled 0

1/1 50 forwarding 4 32 disabled 0

1/1 51 forwarding 4 32 disabled 0

1/1 60 forwarding 4 32 disabled 0

1/1 80 forwarding 4 32 disabled 0

1/1 91 forwarding 4 32 disabled 0

1/1 92 forwarding 4 32 disabled 0

1/1 100 forwarding 4 32 disabled 0

1/1 101 forwarding 4 32 disabled 0

1/1 102 forwarding 4 32 disabled 0

1/1 103 forwarding 4 32 disabled 0

1/1 104 forwarding 4 32 disabled 0

1/1 105 forwarding 4 32 disabled 0

1/1 106 forwarding 4 32 disabled 0

1/1 107 forwarding 4 32 disabled 0

1/1 108 forwarding 4 32 disabled 0

1/1 200 forwarding 4 32 disabled 0

1/1 201 forwarding 4 32 disabled 0

1/1 202 forwarding 4 32 disabled 0

1/1 203 forwarding 4 32 disabled 0

1/1 204 forwarding 4 32 disabled 0

1/1 205 forwarding 4 32 disabled 0

1/1 206 forwarding 4 32 disabled 0

1/1 207 forwarding 4 32 disabled 0

1/1 208 forwarding 4 32 disabled 0

1/1 209 forwarding 4 32 disabled 0

1/1 210 forwarding 4 32 disabled 0

1/1 211 forwarding 4 32 disabled 0

1/1 300 forwarding 4 32 disabled 0

1/1 301 forwarding 4 32 disabled 0

1/1 302 forwarding 4 32 disabled 0

1/1 303 forwarding 4 32 disabled 0

1/1 304 forwarding 4 32 disabled 0

1/1 306 forwarding 4 32 disabled 0

1/1 401 forwarding 4 32 disabled 0

1/1 402 forwarding 4 32 disabled 0

sh spantree stat 1/1 103

Port 1/1 VLAN 103

BPDU-related parameters

port spanning tree enabled

state forwarding

port_id 0x8001

port number 0x1

path cost 4

message age (port/VLAN) 0(20)

designated_root 00-d0-00-f8-30-66

designated_cost 0

designated_bridge 00-d0-00-f8-30-66

designated_port 0x8001

top_change_ack FALSE

config_pending FALSE

port_inconsistency none

PORT based information & statistics

config bpdu's xmitted (port/VLAN) 0(0)

config bpdu's received (port/VLAN) 0(0)

tcn bpdu's xmitted (port/VLAN) 0(0)

tcn bpdu's received (port/VLAN) 0(0)

forward trans count 0

scp failure count 0

Status of Port Timers

forward delay timer INACTIVE

forward delay timer value 0

message age timer INACTIVE

message age timer value 0

topology change timer INACTIVE

topology change timer value 0

hold timer INACTIVE

hold timer value 0

delay root port timer INACTIVE

delay root port timer value 0

delay root port timer restarted is FALSE

VLAN based information & statistics

spanningtree type ieee

spanningtree multicast address 01-80-c2-00-00-00

bridge priority 32768

bridge mac address 00-d0-00-f8-30-66

bridge hello time 2 sec

bridge forward delay 15(15) sec

topology change initiator: 1/0

topology change FALSE

topology change time 35

topology change detected FALSE

topology change count 0

topology change last recvd. from 00-00-00-00-00-00

Other port-specific info

dynamic max age transitions 0

port bpdu ok count 0

msg age expiry count 0

link loading 1

bpdu in processing FALSE

num of similar bpdus to process 1

received_inferior_bpdu FALSE

next state 3

src mac count: 0

total src mac count 0

curr_src_mac 00-00-00-00-00-00

next_src_mac 00-00-00-00-00-00

channel_src_mac 00-00-00-00-00-00

channel src count 0

channel ok count 0

ac-sw-1> (enable)

Re: debugging spanning tree

Hi,

the statistics look really strange.

Why

config bpdu's xmitted (port/VLAN) 0(0)

config bpdu's received (port/VLAN) 0(0)

when

state forwarding ?

I looks like

a) bpdu-filter enabled (but I don't think so)

or

b) too many STP instances on your switch. I've got a feeling you are having a huge number of VLANs on your switch which might exceed the maximun number os STP instances (it's 4096 on Cat4000 is I remember correctly).

Regards,

Milan

New Member

Re: debugging spanning tree

The only vlans running are the ones that show up in the config. I think

we have approximately 30 and not all of them are on the core net.

Kim

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