nice one Trcx. and thanks for the brief description chaterbox0.
Lol, Sorry I forgot. Now I don't have as detailed of a response as I planned, it's been a while since I touch that stuff.
Basically mDNS is the backbone of Apple's bonjour implantation. On a high level it is a way to advertise and discover services on a network. The spec is completely opensource (http://www.multicastdns.org/
) combined that with the fact that requires zero configuration alot of devices are starting to implement it. At the time of my first post in this thread I was in the middle of researching the potential uses for host discovery. You can download mDNSresponder from cydia for a commandline tool that allows you access to the services that it discovers. So far this explanation has sucked so here is a real world example:
You get a new printer and turn it on, you go to your mac and go to set up a new printer and it finds the printer almost instantly. You tell it to connect and with in seconds you are able to print. What happened to make this so painless? mDNS
When you turned on the print it began advertising the fact that it could print, the mac (at your direction) started up the printer applet it asked if there were any printers on the network. The printer responded saying: Yes! I'm at xxx.xxx.xxx.xxx and you print to port 9100. This can obviously be taken beyond just printers. The printer just advertised its service, but that service could be anything, ssh, http, ftp, and much more. Another example is the 'remote' app for iTunes. When you open the remote app on your iDevice it starts advertising that it's a remote, iTunes then can see it and pair with it. The protocol is both active and passive. You can actively send out packets requesting services or you can just listen for new devices to join the network. It's pretty cool.
As previously stated I was investigated mDNS as a means of host discovery. While some what useful it is not overly reliable. Most devices do not support mDNS, additionally most hosts are clients and thus do not advertise. Additionally apple and a few linux distributions seem to be the only ones to us mDNS. Never the less there tend to be at least a handful of devices on the network advertising services. Especially with the advent of iOS 5's wireless sync which used mDNS to discover the computer to sync with. Once again that command line tool can do both active and passive discovery of services and also register service, real or fake so it could cause some trouble, but probably not much.
Wow! That's a lot longer than I though it would be,,,,sorry for the lack of technical detail, but it's been a while, almost 3 months, since I researched it. And if I ever say I'm going to explain something and I don't just PM me about it, because it's very likely that I just forgot, lol.