We are having a storage area network installed in a few days. The vendor who is installing the equipment has requested that we configure the switch being used for what they are calling link aggregation. We will be using a Cisco 3560 Gigabit Ethernet switch for SAN use. What is the best way to set this up?
We are having a storage area network installed in a few days. The vendor who is installing the equipment has requested that we configure the switch being used for what they are calling link aggregation. We will be using a Cisco 3560 Gigabit Ethernet switch for SAN use. What is the best way to set this up?
— Via the Internet.
Check with the vendor to see if they mean port aggregation or link aggregation. Each of these has to be configured separately. For the purposes of this discussion, we will assume that link aggregation is being used. For each grouping of Ethernet ports associated with a particular SAN device, you will want to enter channel-group 1 mode active (this number increases with each port grouping). After entering the first command, the associated port channel interface will be automatically created. Repeat this command for each interface serving the same group.
As you set up the link aggregation, you might want to use the debug etherchannel command to watch what the switch is doing as the link configuration is created. Make sure to use the term mon command so that you can see the messages popup on the screen as you work on the configuration.
Once you have set up the ports in each grouping, go to each port channel interface and make sure that the switchport mode access command is entered. If you will be placing the SAN traffic in a specific subnet/VLAN, you can also enter the switchport access vlan command to associate each port channel. As a nice failsafe option, you can also enter the switchport access vlan commands on the individual ports that the SAN network cards are plugging into. This way, if link aggregation fails for some reason, one of the ports for each SAN device should still work until you can identify the cause of the problem and fix it.
At some point, you will see an error show up on the monitor screen that the ports on the etherchannel group are disabled. Go to each physical port and enter the shutdown command followed by the no shutdown command. The etherchannel configuration should now come online. There are a couple of commands that you can use to get a general idea of who things are working. Do a sh int stat and you should see both the physical gig ports as well as the associated port channel (i.e. po1, po2, etc) all show as connected. A sh etherchannel sum will give you the same details in a different way. You can see all the defined etherchannels, the ports associated with a specific etherchannel and the status of each.
This is just a thumbnail sketch of what is involved in setting things up. There are several good technical documents on Cisco’s Web site that will give you more details. If you find that you created the etherchannel for link aggregation and it should be port aggregation instead, you will need to delete the defined port channels. Although you can’t see it, there is a setting that you wont be able to change, leaving you the only option of deleting the port channel and recreating it as the way to change the configuration.
