Google should be your first call... however,

Simply said an "edge router" is a device that is located at the boundary of your LAN. It is mostly a router that transfers data packets from ATM (asynchronous transfer mode network) or WAN (a wide area network) to your LAN (local area network). In short, edge routers deliver service aggregation and connect several (different) networks together.


To make such a router yourself is not that difficult. You can either go with a (free) off the shelf product like freesco (www.freesco.org), BBIagent (www.bbiagent.net), there are many many other very good ones available, look at other threads... or learn to use iptables
For such a setup in SOHO networks You need:
- 2 nic's (linux compatible offcourse and a decent network chipset, mostly all do)
- a 80486 or better pc (depends how fast and how many simultaneous links you want, and the services you plan to run / monitor / use)
- 16Mb of ram
- a floppy disk and/or cd-rom device