DHCP and Vlans




We have started to implement a Mitel solution using 3300ICP
controllers and 5201,5215 and 5220 handsets. Our network design is 2
w2k DHCP servers with multiple scopes set up and split over the 2
servers these include all the voice and data scopes. we have multiple
stub vlans setup through 2 layer 3 switches (Allied Telesyn Rapiers)
with Layer 3 interfaces on each vlan to allow routing between the
vlans all vlans come back to the same to servers for DHCP using the IP
Helper setup on the Rapiers.

The problem is with the phones hanging at boot the boot method is
below this is taken from the Mitel site

This is the normal sequence of events for a dual port IP Phone, where
VLANs are implemented:
Power up
Run ‘Boot' code
Request IP address (untagged) through DHCP
Receive IP address from default VLAN (data VLAN) and specific phone
and system options
Check VLAN information
Relinquish IP address (untagged)
Request IP address on voice VLAN (tagged)
Receive IP address from voice VLAN and specific phone and system
again Check VLAN information matches, if not repeat until it is.
Locate TFTP server
Get running code
Register with call control
The phone does a double fetch of information, so it is important to
have the same VLAN and priority information in the DHCP server
associated with the data VLAN as it is for the DHCP server associated
with the voice VLAN, i.e. copy the option data. The engineering
guideline that can be highlighted here is that this sequence works
with either multiple DHCP servers on each VLAN, or that the
router/Layer3 switch connecting the VLANs has DHCP forwarding

the phone will receive 2 DHCP offers from the data scope (
(1 from each server) it will then request one of the addresses and
then release it and move to the voice vlan where it will do a DHCP
discover and receive another 2 offers from the voice scope
( from each server)

the offers that the servers are making depend on which server issued
the first address on the data vlan if the address is taken by the
phone then the server will allocated the correct address for the voice
vlan. however the address that was not taken from the 2nd DHCP server
will be reused on the voice vlan even though it is from the wrong


phone - discover
server1- offer
server2- offer
phone - request
server1 - dhcpack
phone - release (phone then moves to voice vlan and dhcp is routed
through rapier using IP Helper

phone- discover
server2 -offer
server1- offer
phone- request
server2- DHCPNACK ( this causes the phone to hang)

I know this is long and complicated and if you have read as far as
this thanks a lot but I could really do with some help on this


James Howie CCNA

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