putting a port in a new port channel breaks uplink

[robertkwild]

hi all,

so normally when i set up a switch(s) i always create a channel group first before i do anything (even if its just one port in the channel group) and when i want to add more ports to the channel group i do

int 1/1/2,(any other ports or a range - i want to add to po)

channel-group 1 mode active

and initialy when i add the ports to the channel group i configure the channel group not the individual ports as its less configuration ie

int po1

switchport mode trunk

switchport trunk allowed vlan add/remove (whatever vlan)

no shut

but trouble is switch B loses connection to switch A as soon as i try to create a new channel group on switch A with the existing uplink port and new port i want to be in the po

is that because i havnt created a po1 on switch B yet thats why as i think that is exactly why

thanks,

rob

[balaji.bandi]

You mean to say Switch A and B have exiting PO running with 1 ports already, if you add one more port, the Port-channel go down and up ?

when you add new port to port-channel that convergence take place, so port-channel go up and down in general.

is this what you facing the problem ?

also provide what switch models and what IOS code, what you see on the logs also help here.

is that because i havnt created a po1 on switch B yet thats why as i think that is exactly why

Port-channel requirement both the side configuration should match - so exiting configuration is changed here.

[robertkwild]

You mean to say Switch A and B have exiting PO running with 1 ports already

no they do not have existing po, as soon as i create one on switch A i persume i lose access to switch B as i need to create a po on switch B aswell, hence why when i create a po i always create a po by default even if one port is in the po as now i need downtime to do this

[balaji.bandi]

yes exiting port should be in port-channel to add one more link that also take part of convergence up and down.

if single link connected using Trunk and want to convert to port-channel, then you removing configuration and added that port to port-channel.

then both the side to be port-channel created and ports should be part of port-channel for the connection to establish.

as soon as i create one on switch A i persume i lose access to switch B as i need to create a po on switch B aswell

you can create port-channel as pre-requisited and shutdown the port-channel

when you add the interface in port-channel config you can do admin no shutdown to bring up the link.

[MHM Cisco World]

complete the config when you end connect the cable 
the STP can down the interface if it detect loop
MHM

[robertkwild]

i feel abit of downtime is needed then as both switches havnt got a single port in a port channel, this is why when i create switches i at least have one port in a port channel so if i want to add a port to port channel i wouldnt have a scenario like this

[balaji.bandi]

Correct - if the both the side port-channel created with single link working, you can add more interface to Port-channel (but there is port-channel convergence take place for the new interface to be part of Port-channel)

[robertkwild]

Is there anyway to do this without downtime?

[MHM Cisco World]

Friend again do config shut the port'

Connect cable 

No shut port 

There is no downtime I think.

MHM

[robertkwild]

So if I do this I can then configure other po on other switch

[balaji.bandi]

Let me write the steps here :

1. Create a Port-channel on both the sides - in shutdown mode

2. Select interface need to be part of port-channel - make necessary confiuraiton - do not connect each other switch

3. same configuration on other interface to be part of the same port-channel (do not connect)

4. Apply similar configuration on SW2

5. connect SW1 and SW2 physical Interfaces

6. issue on port-channel both the side  - no shutdown

7. check show EtherChannel x summary  - Both side should show (P) for both interfaces

[Walston5119]

EtherChannel is a feature that allows you to bundle multiple physical links into a single logical link, and increase the bandwidth and redundancy between switches.

You have explained your configuration steps very well, but there are some things that you need to check and verify before creating an EtherChannel, such as: Kia Finance Login

• Make sure that all the ports that you want to include in the EtherChannel have the same speed, duplex, VLAN, and trunk settings. You can use the show interface command to check these settings on each port.
• Make sure that you use the same channel-group number and mode on both switches. You can use the show etherchannel summary command to check the status and configuration of the EtherChannel on each switch.
• Make sure that you use a compatible protocol for the EtherChannel. You can use either PAgP (Port Aggregation Protocol) or LACP (Link Aggregation Control Protocol), which are dynamic protocols that negotiate the formation and maintenance of the EtherChannel. You can also use the on mode, which is a static mode that does not use any protocol but requires manual configuration on both switches.
• Make sure that you have enough ports available on both switches for the EtherChannel. You can use up to 8 ports for an EtherChannel, but they must be contiguous and of the same type. You can also use different modules or slots for the ports, as long as they are compatible.

[Isabella54]

In the course of setting up EtherChannels between Switch A and Switch B, a connectivity issue has surfaced, leading to a loss of connection from Switch B to Switch A. The standard protocol of initiating a port-channel interface (po1) on both switches has been followed, with initial configurations for trunk mode and allowed VLANs. However, when expanding the EtherChannel by incorporating new ports into the existing channel group on Switch A, a disruption in connectivity occurs. The potential cause lies in the absence or misconfiguration of the EtherChannel on Switch B, prompting a need for a meticulous review of Switch B's settings, including the verification of the port-channel interface and individual port configurations. Troubleshooting steps encompass checking logs for errors, confirming physical connections, and ensuring uniform settings across both switches, while reloading interfaces or switches and updating firmware may be necessary if issues persist. Thorough documentation is also emphasized for effective network maintenance and troubleshooting.

[Ruben Cocheno]

@robertkwild 

You create the Po first and then assign the ports to it, all new ports added afterward will flap/blackhole traffic and some duplicated mac logs might appear due to the bouncing.

Now, if you don't create have a Po from the get-go, you can create the new interface under a Po and then add the old interface back to that new Po. You just need to consider the STP and convergence time.