Problem with spanning tree between C3560 and C2960X

[MH311x]

Hello community,

I need your help.

I changed a switch today (old: C3560,  new: C2960X). The old C3560 was connected to another C3560 over a trunk port.

Since I changed the switch (same config, same vlans etc.) the C3560 on the other side remains root bridge for some vlans, which are going over the trunk port. Some VLANs work, some don't.

I already tried to remove the vlans on L2 and added them again ... I also tried a reboot - nothing changed.

Trunk Port on new C2960X:

interface GigabitEthernet2/0/26
switchport trunk allowed vlan 2,7,8,11-14,23,39,43,44,61,65,152,170,171,666
switchport trunk allowed vlan add 667
switchport mode trunk
ip dhcp snooping trust

Trunk port on old C3560:

interface GigabitEthernet0/1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 2,7,8,11-14,23,39,43,44,61,65,152,170,171,666, 667
switchport mode trunk
ip dhcp snooping trust

sh interface trunk on C2960X:

Port Mode Encapsulation Status Native vlan
Gi2/0/26 on 802.1q trunking 1

Port Vlans allowed on trunk
Gi2/0/26 2,7-8,11-14,23,39,43-44,61,65,152,170-171,666-667

Port Vlans allowed and active in management domain
Gi2/0/26 2,7-8,11-14,23,39,43-44,61,65,152,170-171,666-667

Port Vlans in spanning tree forwarding state and not pruned
Gi2/0/26 2,7-8,11-14,23,39,43-44,61,65,152,170-171,666-667

sh interface trunk on C3560:

Port Mode Encapsulation Status Native vlan
Gi0/1 on 802.1q trunking 1

Port Vlans allowed on trunk
Gi0/1 2,7-8,11-14,23,39,61,65,99,152,170-171,666-667

Port Vlans allowed and active in management domain
Gi0/1 2,7-8,11-14,23,39,61,65,99,152,170-171,666-667

Port Vlans in spanning tree forwarding state and not pruned
Gi0/1 2,7-8,11-14,23,39,61,65,99,152,170-171,666-667

Both switches have the same L2 vlans.

C3560 switch remains root bridge for some vlans ... e.g. vlan 2 has the right root bridge, vlan 7 is wrong.

sh spanning tree C2960X:

VLAN0002
Spanning tree enabled protocol rstp
Root ID Priority 16386
Address XXXX.XXXX.2580
Cost 2
Port 51 (TenGigabitEthernet1/0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32770 (priority 32768 sys-id-ext 2)
Address XXXX.XXXX.1400
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/47 Desg FWD 19 128.47 P2p Edge
Te1/0/1 Root FWD 2 128.51 P2p
Te1/0/2 Desg FWD 2 128.52 P2p
Gi2/0/25 Desg FWD 4 128.81 P2p
Gi2/0/26 Desg FWD 4 128.82 P2p

VLAN0007
Spanning tree enabled protocol rstp
Root ID Priority 16391
Address XXXX.XXXX.2580
Cost 2
Port 51 (TenGigabitEthernet1/0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32775 (priority 32768 sys-id-ext 7)
Address XXXX.XXXX.1400
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te1/0/1 Root FWD 2 128.51 P2p
Gi2/0/26 Desg FWD 4 128.82 P2p

sh spanning tree C3560:

VLAN0002
Spanning tree enabled protocol rstp
Root ID Priority 16386
Address XXXX.XXXX.2580
Cost 6
Port 1 (GigabitEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32770 (priority 32768 sys-id-ext 2)
Address XXXX.XXXX.4c00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1 Root FWD 4 128.1 P2p
Fa0/47 Desg FWD 19 128.51 P2p Edge

VLAN0007
Spanning tree enabled protocol rstp
Root ID Priority 32775
Address XXXX.XXXX.4c00
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32775 (priority 32768 sys-id-ext 7)
Address XXXX.XXXX.4c00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1 Desg FWD 4 128.1 P2p
Fa0/3 Desg FWD 19 128.5 P2p Edge
Fa0/5 Desg FWD 19 128.7 P2p Edge
Fa0/11 Desg FWD 19 128.13 P2p Edge
Fa0/13 Desg FWD 19 128.15 P2p Edge

show cdp neighbors C2960X:

Device ID: 
Entry address(es):
IP address: XXX.168
Platform: cisco WS-C3560-48PS, Capabilities: Switch IGMP
Interface: GigabitEthernet2/0/25, Port ID (outgoing port): GigabitEthernet0/1
Holdtime : 151 sec

Version :
Cisco IOS Software, C3560 Software (C3560-IPBASEK9-M), Version 12.2(58)SE2, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2011 by Cisco Systems, Inc.
Compiled Thu 21-Jul-11 01:44 by prod_rel_team

advertisement version: 2
Protocol Hello: OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=00000000FFFFFFFF010221FF00000000000000260A904C00FF0000
VTP Management Domain: ''
Native VLAN: 1
Duplex: full
Management address(es):
IP address: XXX.168

show cdp neighbors C3560:

Device ID:
Entry address(es):
IP address: XXX.165
Platform: cisco WS-C2960X-48LPD-L, Capabilities: Switch IGMP
Interface: GigabitEthernet0/1, Port ID (outgoing port): GigabitEthernet2/0/25
Holdtime : 148 sec

Version :
Cisco IOS Software, C2960X Software (C2960X-UNIVERSALK9-M), Version 15.2(7)E3, RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2020 by Cisco Systems, Inc.
Compiled Sun 06-Sep-20 12:56 by prod_rel_team

advertisement version: 2
VTP Management Domain: ''
Native VLAN: 1
Duplex: full
Management address(es):
IP address: XXX.165

Any ideas what could cause the C3560 to remain root bridge for these vlans?

[Asemmoqbel · Accepted solution]

Dear MH311x,,

I need  more explanation to clarify your configuration..

the root for vlan 2 is another switch which has MAC (XXXX.XXXX.2580), how is this switch connected to both c3560 and c2960. 

I believe the other switch is somehow causing the other vlans not work.

Please post "sh spanning tree"outputs for all vlans that don't work on both 3560 and 2960

Also, I notice 3560 is connected to 2960 via port g2/0/25 not g2/0/26 based on output of show cdp neighbors.

so also post "show interface trunk" output for g2/0/25 on c2960.

C3560 is root bridge for vlan 7 even though it has default priority because either there is root command to force 3560 to be root or the mac of 3560 is the lowest among the other switches sharing vlan 7.

Best Regards

Asem

[MH311x · Accepted solution]

Hello Asem,

seems like it was a bit too late for me yesterday to have a clear head!

Like you noticed, the cdp neighbor interface was different to the interface I meant to use.

Gi2/0/26 would have been the right interface, but I plugged it into Gi2/0/25. Didn't notice that because my interface description was "right" and I was too unfocused when checking the CDP neighbor config.

Some vlans were working, because the wrong interface included some of the vlans that were also needed on that switch.

The vlans which caused the C3560 to remain root bridge were missing on the trunkport of the C2960X, because I swapped the cables in a hurry. I changed the configuration of the interface, now it's working properly.

Should've seen that earlier... but thanks for your reply & the missing hint.

Also thanks to paul driver!

Have nice weekend & best regards

Michael

[paul driver]

Hello

---

@MH311x wrote:

Any ideas what could cause the C3560 to remain root bridge for these vlans?

---

Both switch's  are not the correct root bridge for either of those vlans.

The 2960  has a root port for both vlans  via <> Te1/01 which isn't the port interconnecting these two switches

The 3560 isnt a root bridge for vlan 2 it has a root port gig0/1 towards 2960 which make sense because the 2960 has an upstream port <te1/0/1> towards the root bridge 

Regards the vlan7 on the 3560, vlan7 is the root bridge because stp is running on gig0/1 however it isnt being seen on the active trunk on the 2950 via 2/0/25 so it isolated as such its become its own root for that vlan.

switch 2960

VLAN0002
Spanning tree enabled protocol rstp
Root ID Priority 16386
Port 51 (TenGigabitEthernet1/0/1)

Te1/0/1 Root FWD 2 128.51 P2p
Gi2/0/25 Desg FWD 4 128.81 P2p
Gi2/0/26 Desg FWD 4 128.82 P2p

VLAN0007
Spanning tree enabled protocol rstp
Gi2/0/26 Desg FWD 4 128.82 P2p

switch 3650
VLAN0007
Spanning tree enabled protocol rstp
Root ID Priority 32775
Address XXXX.XXXX.4c00
This bridge is the root
Gi0/1 Desg FWD 4 128.1 P2p

show cdp neighbors C3560:
Interface: GigabitEthernet0/1, Port ID (outgoing port): GigabitEthernet2/0/25