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VLAN1 10.1.1.0/24

 

VLAN2 10.1.2.0/24

 

VLAN3 10.1.3.0/24

VLAN1 10.1.1.0/24

VLAN2 10.1.2.0/24

VLAN3 10.1.3.0/24

Further Edit:

I guess I've not explained very well what I'm trying to achieve here, but please bear with me a bit here, as I'm not a network guru (just in case you haven't already detected this!).

I don't want to create multiple interfaces on the linux box, as I don't want it doing any routing between VLANs, I just want the box to sit on one of the VLANs (single interface) and forward (or route?) packets via DSL1 or DSL2, depending upon the source of the packet. If 10.1.1.8 is the default route for 0.0.0.0/0 on our network, surely this can be done?

PC on VLAN3 (10.1.3.123) sends a packet to 1.2.3.4. The default gateway on the PC is 10.1.3.1 (i.e. the routing interface on VLAN3), the switch then routes this packet via 10.1.1.1 to 10.1.1.8 (the switch is configured to use this IP as the next hop for 0.0.0.0/0). The Linux box then routes/redirects that packet via the DSL modem 10.1.1.17, because the source IP was within VLAN 3 (10.1.3.0/24). Had the packet of originated from 10.1.2.0/24, then the Linux box would route/redirect via 10.1.1.16

PC on VLAN3 (10.1.3.123) sends a packet to 1.2.3.4. The default gateway on the PC is 10.1.3.1 (i.e. the routing interface on VLAN3), the switch then routes this packet via 10.1.1.1 to 10.1.1.8 (the switch is configured to use this IP as the next hop for 0.0.0.0/0). The Linux box then routes/redirects that packet via the DSL modem 10.1.1.17, because the source IP was within VLAN 3 (10.1.3.0/24). Had the packet have originated from 10.1.2.0/24, then the Linux box would route/redirect via 10.1.1.16