Spanning tree - multiple roots

nkhwaja · ‎12-21-2004

3550 (IOS 12.1(9)) --ISL trunk --> 3550 (IOS 12.1.(12))

'Sho spanning tree active' on both switches shows that its the root for each vlan. How could both switches be root for every VLAN ??

fyi,trunk is operational.

sw2:

ena#sho spanning-tree active

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 000c.30d3.fe80

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 000c.30d3.fe80

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Port ID Designated Port ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr

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

Fa0/48 128.48 19 FWD 0 32769 000c.30d3.fe80 128.48

VLAN0002

Spanning tree enabled protocol ieee

Root ID Priority 28674

Address 000c.30d3.fe80

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 28674 (priority 28672 sys-id-ext 2)

Address 000c.30d3.fe80

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Port ID Designated Port ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr

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

Fa0/5 128.5 19 FWD 0 28674 000c.30d3.fe80 128.5

Fa0/6 128.6 19 FWD 0 28674 000c.30d3.fe80 128.6

Fa0/48 128.48 19 FWD 0 28674 000c.30d3.fe80 128.48

>

sw1#sho spanning-tree active

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 24577

Address 0009.e8f2.4c00

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24577 (priority 24576 sys-id-ext 1)

Address 0009.e8f2.4c00

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Port ID Designated Port ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr

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

Fa0/1 128.1 19 FWD 0 24577 0009.e8f2.4c00 128.1

Fa0/3 128.3 19 FWD 0 24577 0009.e8f2.4c00 128.3

Fa0/5 128.5 19 FWD 0 24577 0009.e8f2.4c00 128.5

..

Gi0/1 128.25 4 FWD 0 24577 0009.e8f2.4c00 128.25

VLAN0002

Spanning tree enabled protocol ieee

Root ID Priority 24578

Address 0009.e8f2.4c00

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24578 (priority 24576 sys-id-ext 2)

Address 0009.e8f2.4c00

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Port ID Designated Port ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr

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

Fa0/5 128.5 19 FWD 0 24578 0009.e8f2.4c00 128.5

..

Gi0/1 128.25 4 FWD 0 24578 0009.e8f2.4c00 128.25

alagrawa · ‎12-21-2004

Hi Nusrat,

In your setup, sw1 should be the root for both vlan1 and vlan2 since it has the lower priority. One reason why sw2 is also showing up as root switch could be if sw2 is not getting BPDUs from sw1.

Check the output of 'show spanning-tree interface fas0/48 detail' multiple times to see if the BPDUs received counter is incrementing or not.

3550#sh spanning-tree inter fas0/48 de

Port 1 (FastEthernet0/48) of VLAN0001 is root forwarding

Port path cost 19, Port priority 128, Port Identifier 128.1.

Designated root has priority 0, address 0009.4381.4700

Designated bridge has priority 32769, address 0005.dcca.1540

Designated port id is 128.13, designated path cost 19

Timers: message age 15, forward delay 0, hold 0

Number of transitions to forwarding state: 2

Link type is point-to-point by default, Peer is STP

BPDU: sent 12846, received 252527 <---------

If the receive counter is not incrementing, then check the same command on sw1 and see if the BPDUs sent counter is incrementing or not. Basically need to check if sw2 is getting BPDUs from sw1 or not.

You might have to SPAN the port and capture a sniffer trace to check if sw2 is actually receving BPDUs or not.

regards

-Alok

nkhwaja · ‎12-21-2004

Thanks for the prompt reply..

In fact, Sw2 (FA0/48) is not receiving any bpdus. But sw1 (FA0/5) is receiving and sending them. What could be wrong ?

SW2#sho spanni int fa0/48 det

Port 48 (FastEthernet0/48) of VLAN0001 is forwarding

Port path cost 19, Port priority 128, Port Identifier 128.48.

Designated root has priority 32769, address 000c.30d3.fe80

Designated bridge has priority 32769, address 000c.30d3.fe80

Designated port id is 128.48, designated path cost 0

Timers: message age 0, forward delay 0, hold 0

Number of transitions to forwarding state: 1

BPDU: sent 335, received 0

Port 48 (FastEthernet0/48) of VLAN0002 is forwarding

Port path cost 19, Port priority 128, Port Identifier 128.48.

Designated root has priority 28674, address 000c.30d3.fe80

Designated bridge has priority 28674, address 000c.30d3.fe80

Designated port id is 128.48, designated path cost 0

Timers: message age 0, forward delay 0, hold 0

Number of transitions to forwarding state: 1

BPDU: sent 316, received 0

SW1#show spanning-tree interface fas0/5 detail

Port 5 (FastEthernet0/5) of VLAN0001 is forwarding

Port path cost 19, Port priority 128, Port Identifier 128.5.

Designated root has priority 24577, address 0009.e8f2.4c00

Designated bridge has priority 24577, address 0009.e8f2.4c00

Designated port id is 128.5, designated path cost 0 Hello is pending

Timers: message age 0, forward delay 0, hold 0

Number of transitions to forwarding state: 1

BPDU: sent 79744, received 39859

Port 5 (FastEthernet0/5) of VLAN0002 is forwarding

Port path cost 19, Port priority 128, Port Identifier 128.5.

Designated root has priority 24578, address 0009.e8f2.4c00

Designated bridge has priority 24578, address 0009.e8f2.4c00

Designated port id is 128.5, designated path cost 0 Hello is pending

Timers: message age 0, forward delay 0, hold 0

Number of transitions to forwarding state: 1

BPDU: sent 79696, received 39815

Prashanth Krishnappa · ‎12-21-2004

Check your trunk configuration and if native VLAN is not 1, make sure that VLAN is created in the VLAN database. Take a look at the following bug

http://www.cisco.com/cgi-bin/bugtool/onebug.pl?bugid=CSCed00396

Prashanth Krishnappa · ‎12-21-2004

Check to see

1)If your trunk is working fine and passing VLANs

2)Check to see if you have any BPDU filtering configured.

3)Check and make sure the VTP domains are the same on both the switches.

nkhwaja · ‎12-21-2004

On SW2, I changed the domain name, and again put the original back to reset the rev#, made it client, then after getting VTP updates, made it server. Defined a new VLAN and saw it propagated to SW1. 'Sho VTP C' shows that joins are being received and transmitted in both switches.

But BPDUs are not being received. I donot see any BPDU filters.

SW1:

interface FastEthernet0/5

description T 3550-Y1ML (replacing Y0U6)

switchport trunk encapsulation isl

switchport mode trunk

no ip address

duplex full

speed 100

>

SW1#sho int fa0/5 trunk

Port Mode Encapsulation Status Native vlan

Fa0/5 on isl trunking 1

Port Vlans allowed on trunk

Fa0/5 1-4094

Port Vlans allowed and active in management domain

Fa0/5 1-2,99

Port Vlans in spanning tree forwarding state and not pruned

Fa0/5 1-2

SW2:

interface FastEthernet0/48

description from X00W-0/5

switchport trunk encapsulation isl

switchport mode trunk

switchport nonegotiate

no ip address

logging event trunk-status

duplex full

speed 100

SW2#sho int fa0/48 trunk

Port Mode Encapsulation Status Native vlan

Fa0/48 on isl trunking 1

Port Vlans allowed on trunk

Fa0/48 1-4094

Port Vlans allowed and active in management domain

Fa0/48 1-2

Port Vlans in spanning tree forwarding state and not pruned

Fa0/48 1-2

SW2#

Kevin Dorrell · ‎12-22-2004

Check there is no SPAN session on the trunk interface on either side, as this can mess up the STP.

Kevin Dorrell

Luxembourg

majorward · ‎12-23-2004

To rectify this issue deploy the following commands:

The primary objective is to have the IEEE 802.1d process differentiate between the primary root and secondary root(if needed)and flood the BPDU out the RP to all non-root DP.

switch3550A(config)#int vlan 1

switch3550A(config-vlan)#spanning-tree root primary

switch3550B(config)#int vlan 1

switch3550B(config-vlan)#spanning-tree root secndary

A) Ensure the portfast feature is disbaled explicitly on the trunk ports.

B) After manipulating the IEEE 802.1d process to your specifications, clar the trunks and or disbale and enable the trunk ports. Or you can wait until the process reconverges and the Max Age parameter of the BPDU will refresh the root ID/Bridge ID in the BPDU.

nkhwaja · ‎12-23-2004

I defined the sw1 as primary, and sw2 as secondary. It changed the sw priority but still SW2 is sending BPDUs but not recieving any, and thats why it still thinks its root..

This looks like a tough one. Earlier, I upgraded SW2 from SMI to EMI (c3550-i5q3l2-mz.121-22.EA2.bin) but no impact.

Any other ideas ?

Prashanth Krishnappa · ‎12-23-2004

Can you email me/post output of following from both switches.

sh ver

sh run

sh cdp neig

sh vtp status

sh interfaces trunk

Prashanth Krishnappa · ‎12-23-2004

Got your email.. Your "s-3550-X00W" switch which is running 12.1(9)EA1c is running into the following issue discussed in the field notice

http://www.cisco.com/en/US/products/hw/switches/ps646/products_field_notice09186a00800c81fc.shtml

Upgrade IOS on this switch as well.