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3500yl Phones appearing on two VLANs, get wrong DHCP address

Roger Spurgeon
Occasional Visitor

3500yl Phones appearing on two VLANs, get wrong DHCP address

I have a network with 6 3500yl switches interconnected. One data VLAN (primary), a wifi VLAN and a phone VLAN. Everything has been working great until a few weeks ago.

I did not make any changes to configurations on the switches, the phone server or any other server, as far as I can remember. But where the phones used to boot up properly, now they will not see the Phone system's DHCP server unless they are plugged into a port specifically marked as on the phone VLAN. If I specifically note the port as untagged on the VLAN 3 (phone), the phone gets the correct DHCP address and everything is great. However, if the port is a "normal" port, then the phone's MAC address appears on BOTH VLANs when booting (1 and 3), the phone gets it's DHCP from VLAN 1. With the wrong IP subnet, it cannot talk to the phone server.

The phones are set to VLAN ID 3 in the phone's config menus.

What I'm trying to figure out is where to look for the problem -- the switch config hasn't changed. The phone config hasn't changed. What could have changed to alter the network's behavior? Some other device on the network causing interference? Any ideas?

Here is my switch configuration:

swBusOfc# sh conf

Startup configuration:

; J8693A Configuration Editor; Created on release #K.12.57

hostname "swBusOfc"
snmp-server location "swBusOfc"
module 1 type J86yyA
module 2 type J86xxA
ip default-gateway 10.103.8.1
ip routing
snmp-server community "public" Unrestricted
vlan 1
name "DEFAULT_VLAN"
untagged 1-38,45-48
ip address 10.103.8.26 255.255.248.0
no untagged 39-44
exit
vlan 2
name "Wireless"
untagged 41-44
ip address 10.30.8.26 255.255.248.0
tagged 45-48
exit
vlan 3
name "Phone"
untagged 39-40
qos priority 7
ip helper-address 10.20.8.1
ip address 10.20.8.26 255.255.248.0
tagged 1-38,45-48
voice
ip proxy-arp
exit

So if I plug a phone into port 39 or 40, it boots great. If I plug a phone into any other port 1-38, I see this as the phone boots:

swBusOfc# show mac-address vlan 1

Status and Counters - Address Table - VLAN 1

MAC Address Located on Port
------------- ---------------
0004f2-2294a0 14
...

swBusOfc# show mac-address vlan 3

Status and Counters - Address Table - VLAN 3

MAC Address Located on Port
------------- ---------------
0004f2-2294a0 14
...

Before this problem, I don't recall seeing the phones MAC address ever appear on the VLAN 1 list.
4 REPLIES
Mohammed Faiz
Honored Contributor

Re: 3500yl Phones appearing on two VLANs, get wrong DHCP address

Hi,

You see the MAC address for the phone in both VLANs as you have VLAN 3 tagged on all the ports (apart from 39 and 40) and VLAN 1 untagged on all the ports (also excluding 39-40). So you are running 2 VLANs to each port.
From your description it sounds like your phones have ended up set to use VLAN 3 untagged rather than tagged.
I'd have a closer look at the phone setups and see if you can see an option for that.

Normally how these things work is that your phone boots onto an untagged VLAN and the DHCP server on that VLAN tells the phone (through a DHCP option) what the tagged voice VLAN is. The phone then reboots itself with the correct VLAN tag in it's config and gets an address from the voice VLAN.
Roger Spurgeon
Occasional Visitor

Re: 3500yl Phones appearing on two VLANs, get wrong DHCP address

Thanks for your reply. We're using Polycom phones, and we've set the VLAN ID on the phone to "3". This worked perfectly. The phone booted into VLAN3, got its IP address from the DHCP server on VLAN3, and all was great.

As of about two weeks ago, this behavior no longer happens. The phone is still set to VLAN 3, but now it is getting DHCP from VLAN 1, not from the DHCP server on VLAN 3. What I am trying to figure out is why it was working but is not now.

I would be thrilled to use this DHCP server option you talk about, but how do you configure that on our Windows 2003 DHCP server?
Mohammed Faiz
Honored Contributor

Re: 3500yl Phones appearing on two VLANs, get wrong DHCP address

The fact that your phones work fine when connected to a port with vlan 3 _untagged_ on it suggests that they are ignoring the vlan information entered into them.
As it points to an issue with the phones I can't really suggest anything other than factory defaulting one of the handsets and trying to re-enter the config.

The setup for the dhcp server is straight forward but you'd need to know whether your phones support this type of operation (we're running a Mitel system that uses this)
Roger Spurgeon
Occasional Visitor

Re: 3500yl Phones appearing on two VLANs, get wrong DHCP address

Thanks again for your input. I have looked deeper into the phones and I think that I have found the setting that changed. I have them booting properly now. I'm not sure how the setting changed, but as long as I know how to make it work, I'm good.

I've also looked into the DHCP discovery, and will be experimenting with that functionality soon.