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Community Member

What is the procedure to modify the channel group settings

We need to change the Channel-group settings in 3750 switch from Mode ON to Mode Active. We have tried once by removing the physical interfaces from the port-channel group but we lost the connectivity to the secondary switch. please give if there is any step by step procedure without losing the connectivity between switches.

Our requirement

From

   channel-group 1 mode on

To

   channel-group 1 mode active

   channel-protocol lacp

2 REPLIES
Cisco Employee

What is the procedure to modify the channel group settings

Hello,

To my best knowledge, there is no easy way of doing this without causing an intermittent connection failure. By removing the entire Port-channel interface using the no interface Po1 command, all physical members will be automatically shut down. On the other hand, if you just remove the physical interfaces from the channel-group without removing the Port-channel interface itself, the ports will go over the STP port role/state determination which may require several seconds for them to become forwarding again. In addition, this requires that the ports are unbundled (i.e. removed from the channel-group) on both interconnected switches within a short timeframe, otherwise switching loops may and possibly will occur.

The most safe way would be to simply use console access but that may not be feasible. In that case, I suggest proceeding as follows (however, please test this in a lab first if possible - I am explicitly warning that this may not prevent a permanent network outage!):

  1. Have SSH/Telnet connection open to both switches
  2. Make sure that the configuration of the bundled ports under a particular channel-group is identical to the configuration of the Port-channel interface itself. Resolve any omissions or discrepancies before proceeding further.
  3. On both switches, shut down all but one physical interface in the channel-group. Leave only one physical link alive in the bundle, all other should be shutdown.
  4. Remove all physical ports from the channel-group on the topologically farther switch without removing the Port-channel interface, using the no channel-group 1 command on the appropriate physical interfaces. Use the interface range command to unbundle all appropriate ports at once.
  5. Using the same approach, unbundle the physical ports on the topologically closer switch.
  6. Because of STP, the connectivity will be disrupted for up to 30 seconds (much shorter with RSTP).
  7. When the connection is reestablished, remove the Port-channel interfaces from both switches before proceeding further.
  8. Reactivate all shutdown physical ports.
  9. Recreate the channel-groups now using the LACP, first on the topologically farther switch, then on the closer switch.

Best regards,

Peter

Community Member

What is the procedure to modify the channel group settings

Hi Peter,

Many thanks for your inputs. Tomm i have scheduled a change to try this, will update you the outcome.

Cheers

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