I swear I had four ideas for mini-programming projects at some point last week. Now I find they’ve evaporated down to one. And even that one has already been thought up before by Kragen. But no-one, to my knowledge, has implemented it, and it’s still a great idea.
I often find myself – as many did at OSCON last week – joining a network with a perfectly fine Net gateway but dead or unresponsive DHCP server. It’d be really useful under those situations to have a program that can deduce the gateway, network mask, spare IPs not in use on the Network, and optionally nearby DNS servers, Web proxies and authorised SMTP relays. You can work out much of these from judicious sniffing of traffic on the network; others you can deduce with some simple heuristics.
Kragen’s thought about this a lot, but makes it sound a lot sneakier than it has to be, because he’s trying to work out tricks to use in case you’re plugged into a switch. On a switch, you don’t see much other traffic. I’d be happy with the autoconfigurator if it only worked on hub-based networks (or wireless networks), where you can see most traffic already.
About the most potentially antisocial act this program would have to do is guess an IP address. If it chose one that was already in use, you’d disrupt that computer’s connection. But a combination of sending out ARP requests, sending out test traffic, and being conservative in your choices (aiming for a reasonable distance away from present IPs, avoiding either edge of whatever netmask you’ve estimated the network to use).