WAN and LAN via the same cable

Question

I've got 4 WAN Internet connections and want to use all of them using router DrayTek Vigor 3300V.

They recommend to connect ADSL modems to WAN ports of router. I cannot connect 2 of modems directly because current network map is:

modem1-\                                                     /WAN3 --- modem3
        --switch1--(long-long cable)--switch2--LAN1 (Vigor) -
modem2-/                                                     \WAN4 --- modem4

I understand that it would be great to make 2 more cables to make

modem1-------------(long-long cable)-----------WAN1          /WAN3 --- modem3
          switch1--(long-long cable)--switch2--LAN1 (Vigor) -
modem2-------------(long-long cable)-----------WAN2          \WAN4 --- modem4

but it's hard to make.

How can I connect Vigor WAN1, WAN2 to switch2 like

modem1-\                                     /-WAN1          /WAN3 --- modem3
        --switch1--(long-long cable)--switch2--LAN1 (Vigor) -
modem2-/                                     \-WAN2          \WAN4 --- modem4

so there will be 3 cables from switch2 to Vigor:

• LAN1 - connects local network to Vigor
• WAN1 - connects Vigor to modem1 via switches
• WAN2 - connects Vigor to modem2 via switches

I think that putting modems to different subnets and using 802.1q can somehow solve my problem but cannot understand how.

Please advise.

Answer 1

You can get some background on VLANs here: How do VLANs work?

In general trying to use VLANs to isolate security-sensitive traffic is a bad idea, but technically speaking you could use VLANs to do what you want. You would need 3 VLANs to carry the traffic. The ports connecting the switches would be configured as trunk ports and the ports connecting the modems to the router would be configured as access ports in their respective VLANs. Giving you specifics is hard w/o knowing what switches you're using.