MS-250 VLAN changing from designated VLAN to default-VLAN

[pammurphy]

Last week my MS-250 stacked switches have been flipping over from the dedicated voice vlan (12) to the default vlan (1) making the phones inoperable.   I have tried setting a  static VLAN on the phone ports to VLAN 12.  This held for about 1 hour and then the switch changed it to VLAN 1.  I have tried changing all the ports to VLAN 1 and deleting the voice VLAN all together.  That worked for a short time but many phones have dropped off the network.  

I have been working with my network support contractor and we have tried many different settings but we have not be successful.

Has anyone else had these issues?  It is now a security issue since I have classrooms without phones.

Thanks

[GIdenJoe]

Are you sure it are the switches that are changing the config to vlan 1?
Your Phones are configured either statically or through CDP/LLDP to use the voice VLAN.  Or in some really obscure cases you use DHCP to provide them the voice VLAN.

So you should do a packet capture on the port and see what lldp and cdp gives in regards to voice VLAN.

If that is still okay then traffic from your phones will either come in tagged or untagged.
And doing captures via dashboard will show you the dot1q vlan tag.

If the frames are arriving on an upstream device on a different VLAN you might have a native VLAN mismatch or hop.  And those can be annoying to find.

[pammurphy]

Thanks - I will try that now.  I have done a few captures so I will go through those to see if I can see anything. 

thanks for the suggestions.

[PhilipDAth]

If you make a config change and the switch loses access to the Meraki Dashboard, it will roll back the change.  Make sure you are not changing the uplink port.

https://documentation.meraki.com/Platform_Management/Dashboard_Administration/Troubleshooting_and_Su...

[pammurphy]

Ran a Wireshark capture and got more data than I was getting in the Meraki captures.   It is showing that after a while the phones are not being discovered by CDP/LLDP - but I have the same switch in another closet that this issue isn't happening to.  

[pammurphy]

Combing through the wireshark log - I determined that I need to separate out more of my traffic.  The ports look like they are being flooded by other traffic than my voice vlan traffic.  I created a test vlan and tested it on a handful of phones.  Those phones stayed in the voice vlan and have successfully stayed connected.  Thank you all for your help and support.