can't /etc/hosts be set up automatically?

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http://askubuntu.com – what I need is: automatically add mac-addresses to some file and manually add the hostnames assigned to them, and a script will then scan my home LAN for those mac-addresses and populate the /etc/hosts file, updating whatever cache. most importantly I do not want a centralized server that works as DNS server 24/7 and consumes a lot of energy in addition to the energy consumed already by the modem offering its own LAN-dhcp services. i.e. I need a decentralized DNS service. has anyone ever heard of such a script? what I want, but I guess that's too much to ask, is some way to automatically read ()