DHCP Multiple VLAN problem

Scott F e_z_now_peeps at hotmail.com
Thu Jul 19 22:10:41 UTC 2007


I am having a bit of a problem trying to get some IP Phones (Mitel) working with ISC DHCP 3

Basically we have 2 subnets set up in a shared network. One is for the
VLAN1 data traffic and the other is for the VLAN 10 voice traffic. The
DHCP Server is in VLAN1 and there is an IP Helpr set up to forward the
DHCP traffic from VLAN1 to 10 (on the 3com 5500). On the VLAN 1 subnet
all the computers are statically assigned addresses by MAC. I have set
up two pools of addresses, one of VLAN1 range and the other on VLAN 10
range. When the phones start up they are on VLAN1 and broadcast for an
address, they get one along with other options that tell it that it
should be on VLAN10, the phone releases its address and comes up on
VLAN10 where it broadcasts and gets an address in the VLAN10 range,
because the request comes from the helper, all seems to work ok.
However, work want to have the pools set so people can't just plug in
any device and get an address, but whenever I put any sort of
conditional statement in DHCPd sees this as the most specific option
and goes to the subnet containing it ignorning whether it has come by
the helper or not. I even tried setting up the 3com switch to add
option 82 info to the DHCP packet so I could ID which VLAN the request
was from, this worked fine except the switch only tagged the first
packet from VLAN10 (the DHCPDISCOVER), the next one ( DHCPREQUEST)
wasn't tagged so the server sees it as being in VLAN1. 

Any ideas anyone? this is driving me up the wall
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