Hot Swapping Voice Vlans

[jziegler]

Hello,

We need to hot swap voice vlans on cisco 7942 IP phones as our companies voice vlan is out of address space. I know, best practice is to have a single broadcast domain per department / switch / etc, but I did not build this mess I inherited it.

Current Topology:

Catalyst WS-C4500X-32 SSO -> WS-C2960X-48FPD-L (Stack Config) -> IP Phone

Voice VLan1

IP Add 192.168.1.254

IP DHCP-HELPER 192.168.10.1

Voice VLan2

IP Add 192.168.2.254

IP DHCP-HELPER 192.168.10.1

Int GI 5/0/1 (IP Phone)

 switchport access vlan 6
 switchport mode access
 switchport voice vlan 1
 srr-queue bandwidth share 1 30 35 5
 srr-queue bandwidth shape 10 0 0 0
 priority-queue out
 mls qos trust device cisco-phone
 mls qos trust cos
 auto qos trust
 no mdix auto
 spanning-tree portfast
 service-policy input AUTOQOS-SRND4-CISCOPHONE-POLICY
end

DHCP Config Settings:

150 TFTP Server IP Address: 192.168.1.15, 192.168.1.16

If I unbox a new phone then connect to voice vlan 2, the phone will retrieve TFTP config files from CUCM, then proceed to boot. However; If I use an existing phone and simply switch the voice vlan then, shut / no shut the port. The phone will never register with the call manager to download config files. The process ends at Config CM List; 192.168.1.15; 192.168.1.16; 192.168.1.254  I am interested in why the last option is shown 192.168.1.254 as it is my gateway and not included in DHCP option 150. 

I have roughly one hundred phones to migrate to this new voice vlan.

If anyone can help ? ! Thanks.

[Dennis Mink · Accepted solution]

I did a similar change the other day and just changing the phones to the new VLANs was enough, I didnt even neet to shut/unshut the port.

The fact that you have functioning phones in VLAN2 proves that routing to and from that VLAN to cucm works. what happens if you first shut the port and then change the vlan to 2 and then unshut the port?

also, are there maybe static IP addresses configured on these phones?  (seeing you inherited a mess ;-)  )

Please rate if useful

[jziegler]

The fact that you have functioning phones in VLAN2 proves that routing to and from that VLAN to cucm works. what happens if you first shut the port and then change the vlan to 2 and then unshut the port?

This did not work either.

also, are there maybe static IP addresses configured on these phones?  (seeing you inherited a mess ;-)  )

No use of static IP address in VLAN2. I created a new dedicated VLAN to split my scope and it only has a single address in it.

I will be running a packet capture on the phone, I will post results.

[jziegler]

Hello,

Could you by chance send me your list of DHCP options? The packet capture has shown a DHCP release and request; however, the client is requesting an ip address in the wrong vlan.

[jziegler]

This is the actual answer to my problems.

https://social.technet.microsoft.com/Forums/windows/en-US/c36b6a70-59a9-40dd-8c1d-aa87a4032aac/possible-to-ignore-renewal-dhcprequest-and-force-dhcp-clients-to-start-over-dhcpdiscover?forum=winserverNIS