Etherchannel: troubleshooting

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