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IP telephone change VLAN


WE have a stack of 3750 switches and have configured ip phones by trunking on a large number of interfaces of the stack.We have a requirement to change the VLAN (associated with voice)on all these ports.What would be the best possible approach with minimum user disruption.Appreciate pointers.

Note we would need to power recycle them to get onto new VLAN and we have trunk config and not voice VLAN(we need to continue)

Many thanks

11 Replies 11


watch out for the following:

1) QoS settings on new VLAN match previous V-VLAN

2) Ensure that IP phones can access TFTP server will helper-address

3) Ensure IP phones will still be able to receive IP address information

4) You can carry out 'Pilot' test on one or few phones to test your methodology.

5) Be ready to deal with any teething issues

6) Run your scripts for testing e.g testing calls and user features such as ex. mobility



Actually, 2) is not an issue. Phones always unicast to tftp, and need no helper-address for that.

You are right. But in a Cisco IOS network helper-address will be required unless you intend to manually configure IP addresses, subnet mask and default gateway on each and every IP phone. Maybe if you are bored this will provide for some light entertainment ; )


Just have the correct option 150 in dhcp as normal, and no helper-address will ever be required.

I had plenty of thins kind of entertainment when fixing things, thanks :)

Aprecciate pointers ...but what has been noticed is that these phones do not pick up the new VLAN auto...they have to be power recycled ...and as there are a large number of phones involved physically doing them is out of option.

They have inline power BUt recyclign switch is out of option...planning to switch off and on the power inline on these ports( to have phones recycle and latch onto new VLAN).

Any experience on this appreciated

1)How can these be done across a lot of int ranges Contigous and non contigous(power inline off and on)

2)Since the users pcs feeding into the trunk off the phones may also be affected ANY gotchas on this would be appreciated

Many thanks


One possible option is that you distribute an email to the users. Obviously tell them changes have been made but for them to take effect the phones must be manually restarted. Of course provide them with the key press sequence required to restart their units.

See here:




Thanks...could you also suggest on the best way to go about doing this without user intervention.Something like disabling power inline on switch range and enabling

Are there any gotchas with this approach and would it do the trick ??


The commmand to use is :

switch(config)interface fastethernet 0/1

switch(config-if)#power inline never

switch(config-if)#power inline auto

Test it out on one phone with PC connected. I understood one of your requirements was to allow the PC to remain connected at all times. If you ask me the downtime is near to nothing. I will try the above command in an hour or so and get back to you with the result on whether the PC will lose connectivity to the network or not.

bye for now


Right. The result of the test was successful. You can turn off inline power if you follow my instructions above. The PC will not lose connectivity to the network.

After you issue 'switch(config-if)#power inline auto'. The IP phone will restart as you required. Remember you can use the interface range command to do changes on multiple interfaces at once.




pls rate this post if it helps.

Thanks...appreciate pointers

So if it were non continuous i would be issuing the command across each interface .

Indeed that is correct. If your interfaces are discontiguous then there is no option other than writing up some script to automate the process. Unless you have a very large environment e.g >1000 then you can consider that. Otherwise it's just going to be a case of methodically going through ranges and individual interface config changes.

all the best


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