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Issues with port-channel not passing traffic in a L2 ring

chad-young
Level 1
Level 1

Hi all!  First time poster, so please be gentle.  My thanks in advance to anyone who can assist.

Anyway, here goes.  I have three sites, all of which hosts various VLANs for multiple kinds of hosts.  A previous tech had set up a trio of L2 switches in a ring and trunked all the active VLANs on the three switches to each other.  The idea was to be able to connect to the VLANs at any of the three sites and have a redundant L2 path between all the sites.  I upgraded one leg to an etherchannel combining two ports into a single 2Gbps pipeline thhrough a Canary CCN-2000 CWDM multiplexer. All links are up, all trunks are up, and the port-channel is up.

Here is the issue - that I can tell, traffic from Site A to Site C is almost entireley *not* going over the faster etherchannel.  It is choosing the slower path through Site B.  AFAIK, spanning tree seems to see the A-C trunk and assigns it a lower cost, but, as far as I can tell, nearly all the traffic is all going taking the other connection.  I admit, though, that my STP-fu is not strong.

I suspect traffic taking the A->B->C path may been the case for a while.  I only noticed it today when adding VLAN 3012 to the trunk.  I made a typo and brought the A->C port-channel down briefly and nothing lost connectivity.  The previous tech noted that when the Site B switch was rebooted last year, traffic did not appear to revert to the A->C direct path.

Am I missing something here?  What do you think might be going on?

http://i91.photobucket.com/albums/k316/caloos2000/trunkedringissue.jpg

Site A to site C trunk config:

Side A Switch:

!
interface Port-channel1
switchport trunk allowed vlan 22,27,33,35,46,49,70,91,95,97-99,101,253,400,777
switchport trunk allowed vlan add 1099,1100,2001,2002,3012
switchport mode trunk

!
interface GigabitEthernet0/47
description Ring Trunks CDC
switchport trunk allowed vlan 22,27,33,35,46,49,70,91,95,97-99,101,253,400,777
switchport trunk allowed vlan add 1099,1100,2001,2002,3012
switchport mode trunk
no cdp enable
channel-group 1 mode on
!
interface GigabitEthernet0/48
description Ring Trunks CDC
switchport trunk allowed vlan 22,27,33,35,46,49,70,91,95,97-99,101,253,400,777
switchport trunk allowed vlan add 1099,1100,2001,2002,3012
switchport mode trunk
no cdp enable
channel-group 1 mode on
!

Site C Switch:

!

interface Port-channel1
switchport trunk allowed vlan 22,27,33,35,46,49,70,91,95,97-99,101,253,400,777
switchport trunk allowed vlan add 1099,1100,2001,2002
switchport mode trunk
!

interface GigabitEthernet0/47
description Ring Trunks Admin
switchport trunk allowed vlan 22,27,33,35,46,49,70,91,95,97-99,101,253,400,777
switchport trunk allowed vlan add 1099,1100,2001,2002
switchport mode trunk
channel-group 1 mode on
!
interface GigabitEthernet0/48
description Ring Trunks Admin
switchport trunk allowed vlan 22,27,33,35,46,49,70,91,95,97-99,101,253,400,777
switchport trunk allowed vlan add 1099,1100,2001,2002
switchport mode trunk
channel-group 1 mode on
!

From site C Switch:

Cleared counters, waited a few minutes and then:

SiteC#sh int port-channel 1
Port-channel1 is up, line protocol is up (connected)
  Hardware is EtherChannel, address is 000a.b841.ddb0 (bia 000a.b841.ddb0)
  MTU 1500 bytes, BW 2000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, link type is auto, media type is unknown
  input flow-control is off, output flow-control is unsupported
  Members in this channel: Gi0/47 Gi0/48
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:00, output hang never
  Last clearing of "show interface" counters 00:01:23
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 58000 bits/sec, 45 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts (0 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     3724 packets output, 596017 bytes, 0 underruns
     0 output error