'Interface Port-Channel' command in etherchannel

[gatecrash]

Dear all,

I'm a little confused about etherchannel configuration, be it pagp or lacp.

I have read through tons of configuration tutorials online and some use the Interface Port-Channel command after configuring their layer 2 etherchannel while others omit it.

What is the purpose of port-channel? Is it some kind of a profile with settings that will pass down to any switchport joining the port-channel?

Take a look at the below config without port-channel, is this valid? If yes, can someone explains when or not to use port-channel? Thanks.

SW1(config)#interface range f0/1 - 2

SW1(config-if-range)#switchport trunk encapsulation dot1q

SW1(config-if-range)#switchport mode trunk

SW1(config-if-range)#channel-group 10 mode desirable

SW1(config-if-range)#end

SW2(config)#interface range f0/1 - 2

SW2(config-if-range)#switchport trunk encapsulation dot1q

SW2(config-if-range)#switchport mode trunk

SW2(config-if-range)#channel-group 10 mode auto

SW2(config-if-range)#end

[Julio E. Moisa]

Hi

Port Channel is a method to provide high availability and more bandwidth efficiently, the Idea is interconnect devices with 2  or more cables (usually up to 8 but on devices like Nexus it can be up to 16 uplinks) in order be seen like only one cable logically, the bandwidth supported for each port will be sum. So If you have 4 links and one is down the service will not be affected because all the traffic will be passing through the other 3 uplinks.  

Your config is related to PaGP (Port aggregation Protocol), it is Cisco Propietary, on PaGP you can use 2 modes desirable (it is like active in LaCP) basically the devices configured as desirable will be enabling the communication and Auto, it works like standby. My suggestion is configure both ends as desirable. 

Once you have configured the channel-group, a virtual interface port-channel will be created automatically with the parameters you need. this port-channels interface can works like layer 2 (Trunks or access mode)  or layer 3 (IP addressing)

PaGP and LaCP are basically equal protocols, the difference are their modes PaGP (desirable/auto), LaCP (active/passive).  PaGP is Cisco Propietary, and LaCP is a open standard version of Etherchannel, in few words it can be used by third party devices. Both protocols work similar. 

Please rate the comment if it is useful

:-)

[Jon Marshall]

Just to add to Julio's post.

With a L2 etherchannel you do not and should not manually create the port channel interface. As Julio says it is automatically created for you and once it is you then apply additional configuration to the port channel interface and this is propagated to all the physical interfaces in the etherchannel.

With a L3 etherchannel you do need to create the port channel interface or at least you did the last time I created one.

Jon

[gatecrash]

So that means port-channel will be automatically created for you after you finish creating the L2 or L3 etherchannel? I'll just need to go into the port-channel interface and configure additional parameters?

So in essence, I do not have to specifically key in the "interface port-channel" command?

Thanks.

[Julio E. Moisa · Accepted solution]

Hi

Once you have selected the interface to be part of the port channel using the command channel-group <group id> mode <mode>

it will create automatically the an interface Po<group id>, so under that interface you can create the parameters to be used and it will replicate the config required to the physical interfaces but in some cases you need to configure some parameters under the physical interfaces as well, for example: 

You has:

interface range fa0/0-1
channel-group 12 mode desirable

then you configure:

interface po12
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan 100,101

I have had experiences where the switchport mode trunk is not replicated so I need to set it up under the physical interface fa0/0 and fa0/1, everything else is replicated. 

You can also use: show etherchannel summary to see the status. 

[gatecrash]

Hi Julio,

Thank you for the explanation. All has been clear to me now. Appreciate the screenshot too.

Thanks Jon too for your invaluable contribution!

[Julio E. Moisa]

Hi,

It was a pleasure 

Have a great day

:-)