Local Area Mobility

So networking companies have been trying to sell us ways to extend layer 2 networks for many years now, back in the days with brouters, Shortest Path First Switching, and even new technologies just out in the last few months such as TRILL and OTV. Now I haven't looked into the new technologies enough to give a thumbs up or down, but since everything in the past has had so many problems I am skeptical.

Looking into it a little though I run into an old gem from the mid 90s (the whitepaper talks about how the new windows 95, with a DHCP client installed, can automatically get an IP address!). Local Area Mobility. Now this may not scale well, but for the problem of a few servers needing to be in the same subnet but a different physical location it works great. In fact it is so simple it blew my mind that I had never heard about or thought of such a thing.

The key is simply that routers use the longest prefix to determine a route. Solution - Host routes.

Local Area Mobility, when turned on, will listen and when a computer is turned on with a statically set IP address that doesn't match the interface's subnet, the router injects a host route (/32) into the routing table. It will also proxy arp requests so that clients in the same subnet (but different router) can still communicate. User attempts to connect to the server's IP, router looks up and finds the /32 hostroute preferred over the /24 or whatever and the packet is properly sent to the server.

I don't know why but that is still blowing my mind how simple it is.

http://www.cisco.com/en/US/products/ps6590/products_white_paper09186a00800a3ca5.shtml