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Duplicate Etherchannel

david de sousa

                   hi all,

i have an small issue with etherchannel, when i create a port-channel in a VSS c6506, the main Po goes down and create another one in parallel with the letter A

Port-channel132        unassigned      YES unset  down                  down

Port-channel132A       unassigned      YES unset  up                    up

132    Po132(SD)       LACP

132    Po132A(SU)      LACP      Gi1/9/12(P)    Gi2/9/12(P)

so my question is, why this duplicate Po ? i know if there is a mismatch between 2 ports, it will create a second port-channel, but here, the two ports are in the same Po but not in the main Po...  if i shut this Po, it will renegociate the Po, sometimes the main Po becomes up, and sometimes no.

i read the Cisco document about the port-channel, but there is no explanation for this comportment. anyone can explain this?

thanks a lot

5 Replies 5

Rising star
Rising star

Do you have this command?

mls qos channel-consistency

According to the document here
a secondary portchannel will be created if :

1. Adding a new port to an existing port channel. If any configuration mismatch is seen on the newly added port, it will be added to Secondary port-channel as you can see (Here, Po1A)

2. Configuration mismatch on the ports bundled in the port channel.

3. Configuration mismatch on the interfaces of the far end device can also create inconsistency between the ports bundled in the port channel.

This is expected behavior. The exact reason will be shown in the Logs while adding the port to port-channel.

Daniel Dib
CCIE #37149

Daniel Dib
CCIE #37149
CCDE #20160011

Please rate helpful posts.

Sandeep Choudhary
VIP Alumni
VIP Alumni

hi ,

These ports are called Aggregator ports Po32A(SU) and are put in a Suspended state

It's  because Port-channel noticed difference in configuration and was not  able to  bundle ports together. Secondary aggregator Po32A will keep the  port up  but will work as a separate port, like you did not have  port-channel at  all. What are these ports connected to?

Please see below link for some more info on aggregartor ports




Can this condition as be caused by port-configuration not being matched. Would having MLS QOS on the 6500 and no MLS QOS on the Nexus 5K links ?


**CAT 6513/SUP720+

interface Port-channel30
description EPH-BUS-N5K1&2_L2
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,60,901,902,904,955
switchport mode trunk
mls qos trust cos                     <--- will removing this resolve the channel group ?


interface port-channel2
description N5K1<>EPH-BUS-CORE1-L2
switchport mode trunk
switchport trunk allowed vlan 1,60,901-902,904,955
speed 1000
duplex full

Bharat Negi

Hi David

I can assume two scenarios:

1. If port settings mismatch:  Both the ports will fall in different port-channel group.  If Gig1/1 & Gig1/2 have a mismatch, then they will form two port channel say Po132 & Po132A (alternate aggregator).  Gig1/1 will be part of 132 and Gig1/2 will be part of 132A.

2. If port settings matches but doesn't match with port-channel settings:  Then both the ports will form a alternate aggregator and main port-channel will remain empty or down - this is happening in your case.

You need to check the port-channel settings or capabilities and compare them with the physical port settings/capabilities.

Just for hint, check flow control or storm-control settings. 



david de sousa

hi guys,

thanks for replies, i have to test it but it seems it was a mismatch in flowcontrol. but i have to test it to be sure.

if it's that, i'll come back to give you my feedback and mark as good answer.

thanks for help,


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