For our example scenario we will simplify things a bit.  We will have Network A, Network B and the internet on our WRT54G running DD-WRT.  (If you need help installing DD-WRT firmware on your WRT click here.)  Network A is the standard internal LAN and Network B is an addition VLAN/Network that we setup.  Networks A and B should be able to route packets freely and both should be able to access the internet. Network A's IP subnet is 192.168.1.0 with a mask of 255.255.255.0.  Network B's IP subnet is 192.168.2.0 with a mask of 255.255.255.0. Port 4 on the WRT will be the trunk with both Networks A and B running as a tagged 802.1q trunk back to our VLAN aware switch (Cisco, Dell, HP etc...). DHCP service will be provided on both internal subnets by the WRT.  For the purposes of this HOWTO we will assume that the ethernet swith on the other end of the trunk is already configured for a 802.1q trunk with VLAN2 tagged and VLAN3 tagged.

While working with a WRT54G at a small office wisu ended up needing to setup a 802.1q trunk between the WRT and a Dell Managed ethernet switch.  The need came about because we wanted to keep the number of switch ports used while setting up the WRT as the default router and firewall for several subnets.  As we investigated what is was going to take to get the WRT54G setup we determined there were a few problems:

1. The default internal LAN network on the WRT is VLAN 0 - VLAN 0 is not supported on most 802.1q capable switches.  Most switches (including ours) start at VLAN 1 and recommend starting at VLAN 2.
2. The web interface for DD-WRT enables VLAN tagging on a per port basis but does not enable each VLAN for tagging.
3. The documentation on this topic is hard to find.

Our scenario

For our example scenario we will simplify things a bit.  We will have Network A, Network B and the internet on our WRT54G running DD-WRT.  (If you need help installing DD-WRT firmware on your WRT click here.)  Network A is the standard internal LAN and Network B is an addition VLAN/Network that we setup.  Networks A and B should be able to route packets freely and both should be able to access the internet. Network A's IP subnet is 192.168.1.0 with a mask of 255.255.255.0.  Network B's IP subnet is 192.168.2.0 with a mask of 255.255.255.0. Port 4 on the WRT will be the trunk with both Networks A and B running as a tagged 802.1q trunk back to our VLAN aware switch (Cisco, Dell, HP etc...). DHCP service will be provided on both internal subnets by the WRT.  For the purposes of this HOWTO we will assume that the ethernet swith on the other end of the trunk is already configured for a 802.1q trunk with VLAN2 tagged and VLAN3 tagged.