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IP phones not getting IP from DHCP server #610545 05/22/17 12:21 AM
Joined: Mar 2004
Posts: 885
dwflood Offline OP
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Joined: Mar 2004
Posts: 885
I've got a customer who recently upgraded their network gear. All their phones (Toshiba IP-5000 series and Polycom 7000s) are having a difficult time with DCHP (they work fine if set for static IPs btw).

What's happening is the phone sends a IP discover, the DHCP server sends the dhcp offer, the phone sends dhcp request but then the process repeats over and over until the phones exhaust all IP's in the DHCP scope or the until the IP lease time expires.

Phones are on a VLAN, their network switch ports are set for tagged and no VLAN number is configured in the phones.

I'm not the network engineer but apparently I have to figure this out as all he wants to do is blame the phones...

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Re: IP phones not getting IP from DHCP server [Re: dwflood] #610557 05/22/17 01:20 PM
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JBean3329 Online Content
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It could be your network has more than one DHCP server active.

My preference would be to set all phone static anyway as it prevents the kind of problem your having. Set them outside the network's DHCP range and you'll have fewer headaches

Sometimes the thoughts in my head get so bored, they go for a stroll through my mouth. This is rarely a good thing.
Re: IP phones not getting IP from DHCP server [Re: dwflood] #610559 05/22/17 01:44 PM
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nameless Offline
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If you're not tagging the VLAN on the handsets, then what's the tagging on the switch for?

Shouldn't you be tagging the VLAN on the handsets?

Though the fact you can see the DHCP offer is strange.
I've seen samsung phones not get DHCP correctly when there was a missconfigured DHCP option.

Also the Samsung ITP-51xx won't work with DHCP when on a tagged VLAN.

Were all the handsets working before the upgrade?

Re: IP phones not getting IP from DHCP server [Re: dwflood] #622121 07/21/18 06:31 AM
Joined: Jul 2018
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wkit Offline
Joined: Jul 2018
Posts: 3
It's common practice to tag the ports on the switch, but then your authorized DHCP server also has to hand out the correct VLAN ID through a dhcp server option. Most often it's based on option 43, but some will have an array of other options that must be used.

The typical method for DHCP addressing is:
1. Connect phone to switch
2. Phone powers on and reaches out for information through default VLAN (unless you already manually tagged it on the phone)
3. Phone either sees DHCP specific vendor settings on default VLAN and gets correctly tagged with a VLAN ID. It then is passed to the correct VLAN and is assigned the correct network address.
4. If no vendor ID/specific option was found or if the phone was not programmed a VLAN ID, it will keep trying.

Polycom instructions are below in one of the answer thread. If you want to assign VLAN ID through DHCP Discovery, you'll need to specify vendor class, set predefined options, specifically option 129, and then give it the VLAN formatted string.

Unfortunately, I didn't find anything for automating the tagging process through DHCP discovery for toshiba ip-5000. Of course, I wasn't searching very hard. If you look through the Toshiba documentation though, you can still manually assign a VLAN. If you do that for the voice vlan # (and the port that the phone is plugged in is also tagged 200, it should go to the correct VLAN on the switch and gets the correct address assignment from the DHCP server.


A couple of things to also note - let's say voice vlan is 200, and default is 1. On vlan 1, the switch should have a default ip/gateway address for vlan 1 - say Vlan 200 should have it's own ip/gateway, say There should be two scopes in the DHCP server. One for and one for Under the scope for - you should have an option 129, specifying a string value of: VLAN-A=200; -- this will allow DHCP to pass VLAN ID 200 to the phone on boot, the phone should then traverse to the correct gateway address and grab it's assigned VLAN network address.

Hope that helps.

Last edited by wkit; 07/21/18 06:54 AM.
Re: IP phones not getting IP from DHCP server [Re: dwflood] #624179 10/04/18 07:47 PM
Joined: Nov 2004
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ur8up Offline
Joined: Nov 2004
Posts: 15
What type of Switch gear is being used. Some IP phones will only operate at 100 meg. you might have to have the network gear set to 100 meg full duplex instead of auto.
You may also want to check IP helper addresses for your Vlan traffic.
Just a couple of thoughts.


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