On Jan 14, 2012 3:18 PM, "Timothy Murphy" gayleard@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.