现在有两台router分别连接上不同的ASDL，有各自不同的ip，两台router距离很近，各有6台电脑连在上面。

为了共享文件方便，希望把这12台电脑放到一个LAN里面？

请问：是不是可以把两台router连起来？有没有可能做一个虚拟的LAN，比如用vpn，但是速度和真正的LAN没有分别？请高手帮忙，多谢。

VPN doesn't improve performance (in fact, it reduces performance in most cases).

All you need to do is to set up a "bridge" (used in the non-technical sense hereafter) between the two LANs. You can either get a router or a normal PC to do the job.

The only tricky part of this is the routing table configuration on your bridge (may it be a router or a PC). Given the two interfaces on this bridge, you'll need to inform each LAN the subnet information of the other, with the bridge itself as the target route.

The simplest way in home / Small office is to connect your two WAN point by a router, and router to the LAN.
Things need to be take care:
1. IGRP / EIGRP should be adopted if your two ADSL have unequal speed (Since only these two support unequal cost load balancing)
2. When you connect LAN segements together, better ensure no switching loop, or otherwise enable STP.
3. Take care when you config your edge router. If static routes are used, make use of polic routing to avoid possible link down.

More advance technology such as GLBP can be used to solve the problem

VPN is definitely resource consuming unless you got dedicated VPN concentrator/firewall.