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DHCP for IP Phone on Cisco Router - 4331 Doesn't work + Cisco 887 Does work

Level 1
Level 1

I have a Cisco 4331 router that was configured with as a DHCP server for a small pool of Mitel iP Phones. The config of this router is a s follows:

ip dhcp excluded-address
ip dhcp pool Voice
 option 43 ascii ";sw_tftp=;;call_srv=;vlan=20;l2p=6v6s6;dscp=46v46s2"
The main LAN interface on the 4331 is setup as a dot1q trunk for VLAN’s 10 (Data) and 20 (Voice). The router makes a DHCP offer but the Mitel IP phone never accepts it, another DHCP request is then made by the IP Phone. The output of ‘show ip dhcp binding’ on the router shows the router offering the IP to be allocated e.g.

RTR01#sh ip dhcp bind
Bindings from all pools not associated with VRF:
IP address      Client-ID/              Lease expiration        Type       State      Interface
Hardware address/
User name    0108.000f.ba4c.30       Nov 02 2017 09:52 PM    Automatic  Selecting  GigabitEthernet0/0/0.20

I move the same DHCP config to a Cisco 887 creating VLAN 10 and 20 and trunking them on Fa0 to the switch and it works fine.

The internal switch is a HP 2920 that is configured to trunk VLAN 10 and 20 back to the respective routers. The keyword ‘voice’ is configured VLAN 20 on the HP.

Using Wireshark (port mirrored from the phone directly) the only difference I can see in the DHCP offer between the 2 x router types is that on the 4331 Option 61 (Client - ID) is in the DHCP Offer reply to the IP Phone (the phone MAC).

In the 887 I don’t see option 61 in the DHCP Offer reply. Should this even matter.

I should have connected the 887 to the same port on the switch as the 4331 and re-tested but the VLAN trunking is the same on the separate ports back to the respective routers.

Can anyone offer an opinion. It’s driving me mad. Better still has anyone got a Cisco 4K config they can share that provides DHCP for a Mitel setup.


Many thanks for taking time to read.





5 Replies 5

Hi @darreng

Not sure why it is necessary to add dscp on the dhcp option if you are not using QoS, but, I've seen others example where the option for dscp is dscp=46v46s26. 

If possible, try to share both switches config so that maybe we can see something you're missing.



-If I helped you somehow, please, rate it as useful.-

Hi Flavio,


Thank you for taking the time to reply. Rather than send the whole switch and router config, I have summarised the key config snippets below. DHCP config is as per the original post on this router.


Port 1/1 on the HP switch stack that shows an IP phone plugged in. Other phones are plugged into the switch, the same config is repeated on those ports.


E.g. VLAN 10 (untagged) and VLAN 20 tagged towards the phone. 

STACK-01# sh vlan port 1/1 de

15:19:59 Status and Counters - VLAN Information - for ports 1/1
Port name: Voice Port
VLAN ID Name                 | Status     Voice Jumbo Mode    
10      DATA                 | Port-based No    No    Untagged
20      VOICE                | Port-based Yes   No    Tagged  

STACK-01# sh cdp neigh de

 CDP neighbors information

  Port : 1/1   
  Device ID : 00 00 00 00 00                                                
  Address Type : UNKNOWN     
  Address      : Unsupported format                                          
  Platform     : MITEL 5320 IP,h/w rev 0,ASIC rev 1,f/w Boot,...
  Capability   : Switch                                                     
  Device Port  : LAN port                                                   
  Version      : MITEL 5320 IP,h/w rev 0,ASIC rev 1,f/w Boot,...


  Port : 1/1   
  Device ID : SEP08000FBA5A70                                               
  Address Type : IP          
  Address      :                                                
  Platform     : M6020001                                                   
  Capability   :                                                            
  Device Port  : Port 1                                                     
  Version      : M6020001                                                   

VLAN 10 & 20 config, note the router is in port 1/48.

STACK-01# sh run vlan 10

Running configuration:

vlan 10
   name "DATA"
   tagged 1/48,4/48,Trk1-Trk2
   untagged 1/1-1/44,2/1-2/44,3/1-3/43,4/1-4/44
   no ip address
   spanning-tree instance 1

STACK-01# sh run vlan 20

Running configuration:

vlan 20
   name "VOICE"
   tagged 1/1-1/2,1/48,2/1-2/3,3/1-3/3,4/1-4/3,4/48
   no ip address
   spanning-tree instance 1

Router configuration shows VLAN 10 and 20 trunked.

interface GigabitEthernet0/0/0.10
 description Data VLAN
 encapsulation dot1Q 10
 ip address
 no ip redirects
 ip nat inside
 standby 10 ip
 standby 10 priority 105
 standby 10 preempt delay minimum 25
 standby 10 track 1 decrement 10
interface GigabitEthernet0/0/0.20
 description VOICE VLAN
 encapsulation dot1Q 20
 ip address
 no ip redirects
 ip nat inside
 standby 20 ip
 standby 20 priority 105
 standby 20 preempt delay minimum 25
 standby 20 track 1 decrement 10




Level 1
Level 1
I have the same issue as you when running ios xe 16.9.1 with Mitel phones. When the main load of the phones is at dhcp will not work. If you upgrade the phones to it will work. I speculate that the phones are dropping the DHCP Offer because the Client ID is passed back to them in the offer. I believe upgrading the phones gets them in compliance with RFC6842 in which the client identifier must be included in the DHCP offer if it is provided by the client. In the older RFC 2131, the server should not include the client identifier in the offer message.


does access port include the both data/voice vlans


is a pc able to obtain dhcp address from the voice vlan scope


On the access port try 

disable cdp

enable portfast 




Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards

Apologies for my delayed response to all those who replied. I haven’t been on the community forums for a while.


In the end we left the 887 providing the DHCP for the site in question. I’ll lab up the recommended changes above to see how things work out. 


Thanks to to all for taking the time to reply.





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