How to set up a port channel on an existing trunked connection between two Cisco 2960 switches

Hello,
I have two switches that are currently connected with a single trunk connection and was wondering if the following was possible:
Can I set up etherchannel on these switches without losing connectivity in the process?
Could I set up the ether-channel on each making sure that I have the next port available ex: port 1 is already trunked and I have port 2 open and available to add to the etherchannel on each switch.
BlakeISSAsked:
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mcsweenSr. Network AdministratorCommented:
I would definitely schedule downtime to set this up.  You likely won't see much network interruption, however, if you make a mistake and loose network connectivity you might be running to the other end of the trunk with your laptop and console cable to undo your changes.

I've put a sample config below as configured on my 2960 switches.
Configure the etherchannel on both switches.
conf t
int port-channel1
description Etherchannel LAG for Trunk to some closet
 switchport mode trunk
 switchport nonegotiate
 load-interval 30
 carrier-delay msec 0
 hold-queue 2000 in
 hold-queue 2000 out

Open in new window

Configure each interface you want to add to the LAG on both switches like this
conf t
int gi1/0/1
description PortChannel1 To SWITCH01 Port gi1/0/1
 switchport mode trunk
 switchport nonegotiate
 load-interval 30
 carrier-delay msec 0
 udld port
 channel-group 1 mode on
 hold-queue 2000 in
 hold-queue 2000 out

Open in new window

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BlakeISSAuthor Commented:
Thank you for your response mcsween. So what I am hearing you say is that if I were to take and configure the ether channel on the two switches with the trunked connection, it would interrupt the connection? I was hoping to be able to have the neighboring port free, set up the etherchannel on each and with the existing trunk connection keep the connection up and then plug in the second cable.  

My alternative plan:
1. Set up etherchannel on two new ports on switch1 and switch2
2. Set the etherchannel on switch2 to passive and set switch1 etherchannel as active (no cables plugged in yet)
3. For both switch port ranges for their respective etherchannels setting  SW TR EN D and SW M T
4. At the switches have the cables plugged into switch1 and ready
5. unplug the trunk and plug the cables that are already plugged into switch1 etherchannel into switch2 etherchannel.
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mcsweenSr. Network AdministratorCommented:
I offer this with the disclaimer that you should test this in a lab before trying it on your prod network.  Spanning tree should fail these over pretty quickly.  There will be an interruption but it should be brief enough that the ethernet protocol can recover before an error pops.

1.

Make sure Spanning Tree is setup at both ends of the trunk

2.

Configure your additional trunk and plug it in at both ends

3.

Configure the etherchannel on both switches

4.

Add the port from the new trunk on the remote switch to the etherchannel

5.

Add the port from the new trunk on the local switch to the etherchannel

6.

Repeat with the ports from the old trunk local then remote
If you really wanted to get fancy you could set vlan priorities between steps 5 and 6 to move the traffic to the etherchannel before you create the interruption on the "old trunk"  Read this article to see how.

http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10555-15.html

If you have a lot of heavy traffic on separate vlans (like cameras and computers) you could use this instead of etherchannel.  This would keep traffic from each vlan on it's own trunk unless there is a failure.
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BlakeISSAuthor Commented:
Well written and concise. Thank you for sharing your knowledge.
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