[CentOS] Is avahi essential?

Mikael Fridh frimik at gmail.com
Sat Jan 14 14:31:04 UTC 2012

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
> >
> > Or, another way of looking at it.  mDNS is a bit like ARP, but for
> >
> > ARP: In a traditional ethernet network, when you try to connect to a
> > machine on your local network with the number then your
> > machine will send out an ARP broadcast packet "whois" 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
> >".  In some cases the machine might say "Who am I?  I'd like
> > to be called Tom"; the dhcp server would respond "You're"
> > 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.

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