Etherchannel is a Cisco term that allows a selection of ports to be grouped into a single virtual connection.
PROS
- Able to move more data than a single dedicated line.
- Provides Redundancy & Instantaneous failover if a line/port does down.
- The switch views the virtual connect essentially just like any other line. ie Protocols like STP and VTP work over it.
CONS
- More Ports used on the switch may have a great cost associated with it.
- 4x100Mb/sec lines means there is still only a max of 100Mb/sec for each individual conversation.
- All Ports have to be Identical (Ie. All FastEthernet or All Gigabit)
- All ports have to be configured the same (ie. Duplex, Speed etc)
Setting up Etherchannel
There are 3 main steps when setting up Etherchannel
- Specify the ports needed
- Specify Etherchannel Protocol. There are 2 main protocols:
- a.) IEEE – LACP
- b.) Cisco – PAgP
- Specify the Channel Group ID and Mode. This is done in the same command.
- a.) Because you can have multiple Etherchannels per switch you will need to specify an ID for each one
- b.) Depending on if you choose LACP or PAgP you will need to specify different modes.
- Turn the Ports into trunking mode
- Because Ports are in trunking mode please also turn on encapsulation ie. dot1q
Commands to setup Etherchannel
Here’s a screenshot from Live Cisco 2960 Switches being setup with Etherchannel:
Switch1
Switch2
What do the happens when something goes wrong with one of the lines with the etherchannel?
Switch2 – Unplug Port fa0/22, wait a few minutes and then plug the port back in:
Let’s go over the last image.
- Unplug cable.
- Look at how fast the etherchannel reports the issue. It’s actually BEFORE the port actually goes down!
- Port goes down
- I hit <enter> a couple of times to break up the output.
- Plug the cable back into port fa0/22
- Interface comes back up
- Etherchannel rebuilds itself
Main commands to troubleshoot:
show etherchannel summary
- Displays info on status of group, port-channel, protocol and port
show etherchannel port-channel
- Displays configured properties of port-channel, port state, protocol, port security, fast switchover and load share. It also lists the ports and timing info.
show interface trunk
- Displays info about all the trunk interfaces.
