EtherChannel Diagnostic Information Gathering
To diagnose EtherChannel problems on a Cisco network, you first must be able to collect information about your switch and its configuration. To perform this task, you, as always, rely on the show and debug commands. First, a brief overview of what you get from the show command.
Switch1> enable Switch1# configure terminal Switch2#show EtherChannel ? <1-6> Channel group number detail Detail information load-balance Load-balance/frame-distribution scheme among ports in port-channel port Port information port-channel Port-channel information protocol protocol enabled summary One-line summary per channel-group | Output modifiers <cr>
Following the typical Cisco command standard, detail gives you more information than you probably want, whereas summary gives you little more than the basics. You should check with summary first, and if the information you need is there, then you are done; otherwise, load up the screen with information from the detail option.
The other options for the show EtherChannel command give you more information about your ports, port-channels, and protocols (PAgP or LACP) if in your troubleshooting you feel that you need to drill down a little deeper. Here is the summary information for the current connection, which reveals the ports that make up the EtherChannel.
Switch1> enable Switch1# configure terminal Switch2#show etherchannel summary 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: 1 Number of aggregators: 1 Group Port-channel Protocol Ports ------+-------------+-----------+---------------------------------------------- 2 Po2(SD) PAgP Fa0/1(D) Fa0/2(D)
In addition to the EtherChannel information, both PAgP and LACP offer further information via the show command. The information can be selected by channel group number and includes counters related to the data that has gone through the links, information about the links that is internal to the switch, and information about the devices on the other side of the EtherChannel links.
Switch1> enable Switch1# configure terminal Switch2#show PAgP ? <1-6> Channel group number counters Traffic information internal Internal information neighbor Neighbor information Switch1> enable Switch1# configure terminal Switch2#show LACP ? <1-6> Channel group number counters Traffic information internal Internal information neighbor Neighbor information sys-id LACP System ID
Here is an example of one of those commands, it is retrieving information about PAgP, using the internal option. You can see in the output that even though you configured the switch, one of the cables is not attached (flag is d), and as such, only half of the EtherChannel is up. With the second cable attached, you see both ports with the SC flags and the H timer running.
Switch2> enable Switch2# show pagp internal Flags: S - Device is sending Slow hello. C - Device is in Consistent state. A - Device is in Auto mode. d - PAgP is down Timers: H - Hello timer is running. Q - Quit timer is running. S - Switching timer is running. I - Interface timer is running. Channel group 2 Hello Partner PAgP Learning Group Port Flags State Timers Interval Count Priority Method Ifindex Fa0/1 SC U6/S7 H 30s 1 128 Any 15 Fa0/2 d U1/S1 1s 0 128 Any 0