Etherchannel: troubleshooting

Etherchannel: troubleshooting

by Cyrus Lok on Thursday, June 3, 2010 at 12:09am

Group Port-channel Protocol Ports
——+————-+———–+———————————————–
1 Po1(SU) LACP Fa0/1(Pd) Fa0/2(P) Fa0/3(P)
2 Po2(SD) – Fa0/4(s) Fa0/5(s) Fa0/6(s)

port channel 2 was down, all members were suspended.

use show etherchannel detail

Group: 2
———-
Group state = L2
Ports: 3 Maxports = 8
Port-channels: 1 Max Port-channels = 1
Protocol: –
Ports in the group:
——————-
Port: Fa0/4
————

Port state = Up Cnt-bndl Suspend Not-in-Bndl
Channel group = 2 Mode = On/FEC Gcchange = –
Port-channel = null GC = – Pseudo port-channel = Po2
Port index = 0 Load = 0x00 Protocol = –

Age of the port in the current state: 0d:00h:16m:10s

Probable reason: dtp mode of Fa0/4 is on, Po2 is off
Port: Fa0/5
————

Port state = Up Cnt-bndl Suspend Not-in-Bndl
Channel group = 2 Mode = On/FEC Gcchange = –
Port-channel = null GC = – Pseudo port-channel = Po2
Port index = 0 Load = 0x00 Protocol = –

Age of the port in the current state: 0d:00h:16m:10s

Probable reason: dtp mode of Fa0/5 is on, Po2 is off
Port: Fa0/6
————

The reason is very clear.

2950-1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
2950-1(config)#int po2
2950-1(config-if)#swi
2950-1(config-if)#switchport mode trunk
2950-1(config-if)#do sh ether summ
Flags: D – down P – in port-channel
I – stand-alone s – suspended
H – Hot-standby (LACP only)
R – Layer3 S – Layer2
u – unsuitable for bundling
U – in use f – failed to allocate aggregator
d – default port

Number of channel-groups in use: 2
Number of aggregators: 2

Group Port-channel Protocol Ports
——+————-+———–+———————————————–
1 Po1(SU) LACP Fa0/1(Pd) Fa0/2(P) Fa0/3(P)
2 Po2(SU) – Fa0/4(Pd) Fa0/5(P) Fa0/6(P)

Port channel 2 was not a trunk. Explicitly set to trunk solved the problem.

Another command similar to detail is 2950-1#sh etherchannel port-channel

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One Response to Etherchannel: troubleshooting

  1. Dan S says:

    Thanks for your post! I ran in to the exact same problem. The CCNP training manual I have doesn’t talk about how the etherchannel becomes it’s own port that may not be configured by default in the same way on the other switch. My 3550 and 2950 decided on different setups apparently. Putting both of the etherchannel virtual ports into explicit trunking modes fixed it! 😀

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