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Cisco trunking problem

Posted on 2011-02-10
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Last Modified: 2012-05-11
I have trunked a 2900xl switch up to a 3550 and can get it to work fine with just one cable from F0/10 on the 2900xl to F0/10 on the 3550.  I can ping successfully across from one laptop to another.  When I add a second trunk and cable from the 2900xl port F0/9 to the 3550 port F0/9, I lose the ability to ping from a host on one switch to a host on the other switch.   Port F0/10 was ROOT and is now blocked, whereas F0/10 was originally ROOT.  

What in the world would cause this to stop working?  STP gone awry?   Are you supposed to use Etherchannel in this situation to bundle them together and NOT have 2 separate trunks?  

2900xl config:
interface FastEthernet0/9
 description 'Trunk to port F0/9 on 3550 switch'
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 1,10,1002-1005
 switchport mode trunk
!
interface FastEthernet0/10
 description 'Trunk to port F0/10 on 3550 switch'
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 1,10,1002-1005
 switchport mode trunk
!
interface FastEthernet0/12
 description 'Laptop access port for ping test'
 switchport access vlan 10
 spanning-tree portfast

3550 config:
interface FastEthernet0/9
 description 'Trunk to port F0/9 on 2900xl switch'
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 10
 switchport mode trunk
!
interface FastEthernet0/10
 description 'Trunk to port F0/10 on 2900xl switch'
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 10
 switchport mode trunk

interface FastEthernet0/12
 description 'Laptop access port for ping test'
 switchport access vlan 10
 switchport mode access

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Question by:B1izzard
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11 Comments
 
LVL 6

Expert Comment

by:gcl_hk
ID: 34869754
Which switch is the root bridge you mean? also provide "show spanning-tree" report on both switch
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Accepted Solution

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torvir earned 250 total points
ID: 34869916
The best way to do this is of course an ether channel. Then you have more bandwidth to play with when both links are up, but still have redunancy. Even better is that you don't have to wait for STP-negotiation (up to 50 seconds) when links goes up or down.

By the way, did you wait more than 50 seconds to see if you get ping contact again?
Just so you didn't jump to conclusions from a too short test.

But This problem of yous is a true mystery. Do you use PVST or Rapid spanning tree or even MST.
MST could be a problem here because it depends on vlan 1.
Another thing is that you have different "allowed vlan" in either end of the cable. I can't see how this could have an impact. But try to change to the same allowed vlan anyway.
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Author Comment

by:B1izzard
ID: 34871897
At first the 2900xl was the root bridge, so I decided to force the 3550 to be root on vlan 1, and still it wouldn't ping through.  I then I changed vlan 10 on the 3550 to force it to be root and it started working.  When I changed back to force the 2900xl to be root on vlan 10, it failed again.

After changing the 3550 back to root, it wouldn't ping through until I unplugged port F0/9, waited, then plugged it back in and everything worked as it should.  So something doesn't seem to work right when the 2900xl is root.  

I was using RPST on the 3550 and PVST on the 2900xl, but I tried changing them both to PVST with no effect.  

I have waited for more than a minute on all ping tests, so I'm sure it's not me being impatient, but good to point out!

Ever run into where you had to force a newer switch to be root to get things working?  The 2900xl is really old BTW.
0
 

Author Comment

by:B1izzard
ID: 34871937
2900xl#sh spanning

Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, address 0004.9ad8.a880
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 4097, address 000e.384f.c980
  Root port is 22, cost of root path is 19
  Topology change flag not set, detected flag not set, changes 15
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0

Interface Fa0/9 (port 22) in Spanning tree 1 is FORWARDING
   Port path cost 19, Port priority 128
   Designated root has priority 4097, address 000e.384f.c980
   Designated bridge has priority 4097, address 000e.384f.c980
   Designated port is 9, path cost 0
   Timers: message age 2, forward delay 0, hold 0
   BPDU: sent 15578, received 885

Interface Fa0/10 (port 23) in Spanning tree 1 is BLOCKING
   Port path cost 19, Port priority 128
   Designated root has priority 4097, address 000e.384f.c980
   Designated bridge has priority 4097, address 000e.384f.c980
   Designated port is 10, path cost 0
   Timers: message age 3, forward delay 0, hold 0
   BPDU: sent 15755, received 974

2900xl#sh spanning vlan 10

Spanning tree 10 is executing the IEEE compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, address 0004.9ad8.a881
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 4106, address 000e.384f.c980
  Root port is 22, cost of root path is 19
  Topology change flag not set, detected flag not set, changes 20
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0

3550#sh spanning

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    4097
             Address     000e.384f.c980
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    4097   (priority 4096 sys-id-ext 1)
             Address     000e.384f.c980
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/9            Desg FWD 19        128.9    P2p
Fa0/10           Desg FWD 19        128.10   P2p


VLAN0010
  Spanning tree enabled protocol ieee
  Root ID    Priority    4106
             Address     000e.384f.c980
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    4106   (priority 4096 sys-id-ext 10)
             Address     000e.384f.c980
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/9            Desg FWD 19        128.9    P2p
Fa0/10           Desg FWD 19        128.10   P2p




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LVL 17

Expert Comment

by:MAG03
ID: 34872077
You must include the native vlan in the allow list as tagged vlans are transported over the native vlan (vlan 1 is native by default). if you are just going to use one vlan over a port you do not need to trunk that link.
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LVL 5

Expert Comment

by:torvir
ID: 34872146
I see nothing strange here. Did it work during the time you typed these commands?
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LVL 17

Assisted Solution

by:MAG03
MAG03 earned 250 total points
ID: 34872285
you can also try adjusting the priority of the new switch by doing one of two things:

(config)#spanning-tree vlan 1-1005 priority 0 (configures the switch as the bridge for all vlans)

or

(config)#interface fa0/9
(config-if)#spanning-tree vlan 10 priority 0 (configures the port as root for vlan 10)
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Author Comment

by:B1izzard
ID: 34872373
>> Did it work during the time you typed these commands?  
Yes, at the point of doing the 'show' commands it was working.

I change it to enable vlan 1 and it wasn't working, but perhaps they just needed a reboot.  Ok, so vlan 1 is always required when trunking?
Anyone run into anything like this before where you had to force the 'root'?
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LVL 17

Expert Comment

by:MAG03
ID: 34873633
strange, perhaps a reboot will do the trick.  Another thing to try is to trunk another port on each switch and see if the problem persists.
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Author Comment

by:B1izzard
ID: 34879900
I'm probably going to buy a couple more 3550's today and setup everything up again from scratch with the same IOS on all.  I don't feel like having the really old 2900xl switches in the mix with a much newer 3550 is helping any.  
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Author Closing Comment

by:B1izzard
ID: 34923770
I set it up using Etherchannel and it is working ok.  Thanks for your assistance.
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