vlan and "Campus situation"
 

I've been asked to upgrade a network in a sort of "Campus"...
At this moment the uplinks to the Internet consists of 2 ADSL-connections that are NATted using a Fritz! modem/router that has been opened as a Linux device using Freetz.

The Fritz! has a 4-port switch and it should be able to create VLANs on them, but I have a feeling this is being discouraged by AVM and I could not get it to work.

To separate at least some networks my predecessor used NAT-routers behind NAT-routers, which is not an elegant solution but working.
I was given a Netgear GS108E Plus Switch which supports VLANs.
I thought it was now easy to separate networks behind the NAT-router.
Using port-based routing I configured Port 1 as "all" and the subsequent ports (2...8) as VLAN 1..7
With port 1 connected to the router I was able to communicate using the VLANned ports, but I wasn't able to get an IP using DHCP. I think this was to be expected as the answer from the DHCP-server will not be broadcasted over the VLANs (or should it?).

This configuration will be of no use to me as I don't want to have a DHCP-server on each LAN. I thought I would have some kind of DHCP-relay feature on my switch. Do I really need such a (probably more expensive) switch or do I have some more possibilities with the current hardware?