On Jan 14, 2012 3:18 PM, "Timothy Murphy" <gayleard at eircom.net> wrote: > > Stephen Harris wrote: > > >> >> As far as I can see, it is some sort of rival to dhcpd. > >> > > >> > No, DHCP is used to assign network addresses and routes (and other > >> > optional configuration items). > >> > >> According to the Wikipedia entry for mDNS, > >> "Using mDNS allows to determine the IP address of a host > >> without the help of a centralized DNS server". > >> > >> Isn't that more or less what I said above? > > > > It's almost the opposite. mDNS does name->IP and let's people > > find other machines; DHCP does MAC->IP and let's a machine find _itself_. > > > > Or, another way of looking at it. mDNS is a bit like ARP, but for names. > > > > ARP: In a traditional ethernet network, when you try to connect to a > > machine on your local network with the number 10.20.30.40 then your > > machine will send out an ARP broadcast packet "whois 10.20.30.40" and > > then the machine in question will respond with its MAC address and then > > the machines can talk via ethernet. > > > > mDNS does something similar, but for names mapping to IP addresses; so > > your machine will broadcast out requests for names ("whois fred") and > > get a response. mDNS-SD can also do service discovery ("who is running > > samba?", "who is running iTunes?"). This allows applications to find > > local resources. > > > > All this is done without a central server. > > > > DHCP is almost the opposite; it's for a machine to find out what _it_ > > is; the machine asking "Who am I?" and the server responding "You're > > 10.20.30.40". In some cases the machine might say "Who am I? I'd like > > to be called Tom"; the dhcp server would respond "You're 10.20.30.40" > > and _might_ update a central DNS (or, more often, might not). > > OK, I should have said "a rival to ARP + dhcp". > As I see it, dhcpd assigns IP addresses to the devices on a LAN, > and arp then provides a method of accessing a device > with a given IP address. > > Incidentally, I don't really see why mDNS is needed on a LAN. > If a program wants to know the IP address of a device with a given name, > why can't it just look in /etc/hosts ? Yeah if all servers on the lan somehow magically ended up in the hosts file I wouldn't install avahi either. > but if there is a server available, I don't really see the point of it. I think that's been said already.