DHCP options 125 or 128, 129, 130, 132, 133. Sonicwall should have IP Helper configuration under Network/IP Helper. Create the sub interfaces and connect the Parent interface to layer 2 switch (VLAN Trunk). Create IP Helper to forward from VLAN interface to the DHCP server IP. Option 125 is a string: id:ipphone.mitel.com;sw_tftp=<Server IP address>;call_srv=<Server IP address>;vlan=<VLAN ID>;l2p=1;mode=minet . Option 128: <Server IP address>, Option 129: <Server IP address>, Option 130: MITEL IP PHONE (case sensitive), Option 132: (Long) <VLAN ID>, Option 133: (Long) 6. You also need either port based VLAN tagging on the switch or you will have to statically set the VLAN ID on the phone and PC.
Use Option 43!!! It is SOO MUCH EASIER, and the way the manual recommends, plus it is the only way if you have the older Inter-Tel IP phones (although a little trickery is needed to use one option for both phone types). Plus almost all Mitel phones will recognize it and use it, and most DHCP servers/routers have a way to do this, except basic SOHO routers.
Note that option 125 is NOT a dumb text string... it is an encapsulated option, using just an ASCII text string will fail.
Note: The 5000 doesn't act as a DHCP server.
Ralph
Correct, currently that is... the rumor mill (ie. tech support) says this is coming, probably in the next major version release.
The easiest way to do DHCP for Mitel phones in a network with a 5000 that doesn't have a DHCP server capable of handing out the correct options is to purchase a used PC or older server that is Linux compliant (or the customer may have an old PC/server laying around, those old Windows Server 2000/2003 boxes work great), and install MSL but do not license it or register it with AMC, then you have gained two (possibly 3) very useful tools, a SMTP email relay server, a Mitel compatible DHCP server, and if needed it can be a router or inter-VLAN gateway as well. We typically use some 3-4 year old dual-core HP business class PC's from state surplus that we get for $40-$80, works like a champ! Or if the customer insist on a new unit, there are sub-$300 PCs that work well available from many vendors.