Add Port a existing Channel-group

[Hubsi-Smith]

Hello,

I have a stupid question. I have 2 Cisco 3750x switches with a configured channel-group. How could I expand this channel-group group to add another port?

I have configured on both sides:

channel-group 1 mode on

interface Port-channel1
 switchport mode trunk
!
interface FastEthernet0/1
 switchport mode trunk
 channel-group 1 mode on
 shutdown
!
interface FastEthernet0/2
 switchport mode trunk
 channel-group 1 mode on
 shutdown
!

When I first bring up 0/1 there is a downtime for 30 seconds. When now 0/2 is going up, the channel will be disconnected until 30 seconds and than both are alive. I don´t know why... what does the switches do on the background?

[balaji.bandi]

Downtime the whole network for 30Seconds? how is your network? what is another device?

what is the reason for channel mode  ON, why not use LACP, (do you have other side constraints ?)

Once the port-channel up and running, you can have many interfaces without any downtime.(based on limitation of port-channel)

Looks for me more of STP converge time,

we need more information and network connected?

[Hubsi-Smith]

No, there aren´t any constraints. Only that some switches are in a stack.

Okey, if I understood it right, when I switch both sides of the switches in the "mode on", I got a channel but none PAgP.

I tried that with Packet Tracer and yes, when I disable a port the whole connection is going down.

I think the best solution for me is to use the auto/desirable config. So I will got a PAgP Channel and I could ports en-disable and the whole channel isn´t going down.

I still will play with Packet Tracer before I update my production enviornment.

[paul driver · Accepted solution]

Hello

If the port channel is already up then all you need to do it add an the additional interface to the existing PC on both switches  and enable them, You shouldn't really experience any stp convergence unless you drop the primary interface 

sw1-2
int x/x
description new port for PC
shutdown
switchport mode trunk
channel-group 1 mode on
no shut

[Hubsi-Smith]

Works flawless... thank you for your help.