what's needed to make hostname resolution work on a lan?

Question

I am developing a networked application that runs on a few different computers on a LAN. One of the core needs is for the app to maintain a list of peers on the LAN with which it has communicated in the past, so that it can restore previous sessions. The naive solution would be to just remember the IP and store it in a table, but what happens when the IP of a peer changes?

Instead, I thought I'd store the hostname of the peers so even if the IP changes they will still be reachable via their hostname. (I know hostnames can change as well but that is good enough).

So my question is what exactly is needed to make hostname resolution work on a LAN with mixed Windows/Mac/Linux clients?

Solution

Without the use of a central authority the only reliable way to achieve this is through the use of zerconfiguration name resolution. This means that without a multicast router you will only be able to dynamically resolve peers on the same subnet as the resolving host. You could use something like bonjour for mac, netbios or ssdp for windows or avahi for linux but you can't assume that these are enabled. I may be overlooking some more popular protocols that perform this function well but I would personally throw together a quick udp broadcast name resolution protocol for your application. Take a look at these for some more ideas:

Zeroconf Name resolution

Universal local network name resolution method without DNS?

http://en.wikipedia.org/wiki/Zero_configuration_networking#Name_resolution

http://en.wikipedia.org/wiki/Broadcast_address#IP_networking

I would pick a specific udp port to listen on (lets say 12000) and then when you're ready to resolve hosts send a "hello" udp packet out to 255.255.255.255 on port 12000 and all of the other hosts on your network running your app should reply with a packet containing their hostname, possibly other information.