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Err-disable Loopback Between Cisco and Nortel Portchannel

I have a LACP portchannel between a Cisco 3750 and a Nortel(Avaya 5650). There are two interfaces that are part of the portcahnnel but, one of the ports on the Cisco is err-disabled with loopback. I've read that the loopback err-disable feature disables the port when a loop is detected that spanning tree didn't detect. The Cisco switch is running PVST. Could this be a problem.

Must the native VLANs match between the Cisco and Nortel switch? I'm assuming yes - like Cisco and could this be the problem as the Cisco switch portchannels native VLAN is 1 and the Nortels portchannels native vlan is 301.

Thanks, Pat.

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Err-disable Loopback Between Cisco and Nortel Portchannel

Hello Pat,

native vlan must match on an 802.1Q trunk also in a  bundle or you could have connectivity issues on IP subnets associated to involved Vlans.

for the loopback issue what happens if you shut and unshut the affected port?

Hope to help


New Member

Err-disable Loopback Between Cisco and Nortel Portchannel

There seems to be no connectivity issues between user VLANs as the trunk is up with the one interface. I will have make any changes off hours - even the shut no shut so I can't do that now but, even if I did it still has a different native vlan than the Nortel.

So, off hours I am going to change the native vlan of the Cisco switchports that are part of the portchannel to 301 - same as the Nortel. Hopefully this will resolve the loopback error-disable problem I am seeing but, aren't there some caveats with spanning tree when connecting Cisco with Nortel?

Thanks, Pat.

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