I would like to use a linux machine to act as a DHCP server across multiple VLANs.
Will the following work?

1. Use a Layer 3 Switch which has DHCP relay functionality built in to assign the VLANs by IP address
2. Use a normal kernel without VLAN support on a linux box that is configured with a range of virtual interfaces (e.g. eth0:1 etc) but which is plugged in to the trunking port on the switch.
3. Assign DHCP addresses accordingly per virtual interface

If this is a bad way of doing things, I would be interested in knowing why, and also if people have experience with the VLAN patch for the kernel what there view of it has been.

I used the VLAN patch with 3Com superstack switches and I was unable to get it to work reliably.

This may well have been due to the fact I was using FreeSWAN at the same time. FreeSWAN is famous for its ability to break low level network protocols

Regards

That matches what I have heard about VLAN+FreeSwan which is why I want to just use IP routing on the Linux box without it having to know anything about VLANs but not sure if it will work.

What about without FreeSwan?

My only real reason to use the VLAN patch was to try to tidy up the cabling on the primary and secondary firewall at a company I used to work for.

As each server had 10 physical NICs, you can imagine the cabling was a little spaghetti-ish.

FreeSWAN was essential, so the VLAN patched got dropped.

Regards

Another question:
If the kernel does not have VLAN support but I use a NIC which does and then bind multiple virtual interfaces to that card, will clients on multiple VLANs be able to all access that server?

That depends on your VLAN implementation. VLAN tagging is simply another layer round an ethernet frame that indicates what VLAN it belongs to. The hardware should handle it transparently but, of course, YMMV.

Regards