Sometime someone connects his computer to mine using a network cable, to transfer some files or similar. In a perfect world, both computers would run something like zeroconf or avahi-autoip, and IP adresses were taken care of. But in the real world, this is not often the case. Then, this would be easiest:
$ ifconfig eth0 192.168.42.1 $ simpledhcpd eth0
Where simpledhcpd would, without any configuration, start listening for DHCP requests on eth0 and serve IPs from the just configured subnet. No configuration file, no leases, not even a deamon mode. Just Real Simple IPs for your ad-hoc-network. Does that already exists?
Have something to say? You can post a comment by sending an e-Mail to me at <mail@joachim-breitner.de>, and I will include it here.
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The closest thing I can think of: dnsmasq works fairly well with little-to-no configuration, and what little configuration you might want you can do with command-line options if you don't want a configuration file.
Oh, and in a *perfect* world, both sides would run IPv6 and would automatically have a unique link-local address on interfaces in addition to whatever other address that interface might have.