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Old 07-20-2009, 05:31 PM   #1
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DHCP Config for VLAN's using 1NIC and non VLAN router.

I am trying to figure out a way for DHCP to assign 1 scope to VLAN capable devices and another scope to non VLAN devices.

We are using grandstream GXP2000 Voip Phones that have a mini router built in. The phones are VLAN capable. The workstations are plugged into the mini router. The phones DHCP request is tagged and gets assigned an IP address from the phone vlan scope. The the mini router forwards untagged packets from the computer's dhcp request and receives an IP address from the computer non vlan scope.

I would like to have linux perform the inspection of tagged status and then have DHCP reply from the correct scope without the help of a VLAN Router.

Or, is it possible to delay the DCHP reply from the phone VLAN scope, so that the non VLAN scope will be assigned first for the computers, and then the phones second?

here is my setup:

eth0 main lan for computers
DHCP scope for computers
eth0.121 Phone VLAN
DHCP scope for phones

Now the only question is how to make sure the correct devices are assigned in the right scope.
Old 07-22-2009, 02:41 AM   #2
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A "mini router"? Are you sure it is and not a bridge? The way a voip phone works is generally that it uses a tag for it's own traffic and then bridges the traffic for a default vlan to the "PC" port, sometimes permitting tagging of that traffic too on the LAN uplink.

You've not said anything about the switch you're using, and that's more interesting in this scenario. Normally you'd just configure a 802.1q setup on each port on the switch and something similar for your server and then just configure dhcp to listen to two different subnets. In all likelihood if your switch is actually just a bargain bin 20 job and doesn't truncate the ethernet frames then you should be able to get away with completely ignoring the vlans on the switch, as long as the dhcp server is expecting the same tagged / non-tagged traffic as the phones are dishing out by means of a proper vlan setup on the server, then that would most likely also be fine.


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