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Interesting troubleshooting with Cisco Nexus 1000V

with 2 comments

Today, I assisted a couple of coworkers with troubleshooting a VLAN issue. The VLAN had been added to all the appropriate devices, but the VM was still unable to ping the gateway. As our troubleshooting progressed from device to device, we noticed that although the uplink port profile on the Cisco Nexus 1000V was configured correctly, the VEM on the host was not updating with the changes. This could be seen by running

vemcmd show port vlans

on the host itself. As we dug through the running config of the Cisco Nexus 1000V, we noticed that besides the port channels inheriting the uplink port profile, a VLAN was manually added to all port channels. It turns out this is a simple fix (after many hours of troubleshooting). By issuing the command

default switchport trunk allowed vlan

to all the port channels, the port channels started inheriting the VLANs from the port profile again. We verified this by adding/removing a VLAN and the port profile updated as expected. We are not sure when this VLAN was added this way, but it did give us a bit of a headache.

So remember when working on the Cisco Nexus 1000V, add/remove VLANs via the port profiles, not from the port channels or ports themselves.


Written by jguidroz

March 8, 2012 at 5:26 pm

Posted in Networking

2 Responses

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  1. That’s kind of a strange problem. I’ve seen minor glitches where adding a native VLAN to an uplink port profile didn’t actually get programmed into the VEM without a restart. What version are you running?


    March 10, 2012 at 2:55 pm

    • The version of the 1000V was 4.2(1)SV1(4). We can only conclude it was from someone make the configuration change directly to the port channels and not the port-profile. Hopefully we can do further testing to verify this.


      March 12, 2012 at 9:17 am

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