zeroconf networking in Debian
I know essentially nothing about zeroconf networking, but I thought I'd try
to get it working on my laptop, so I'll be ready to use it at the next
DebConf, ad-hoc wireless network, DNS-less office
The first thing I tried was the zeroconf package. This makes interfaces
get assigned an ip address in the link-local 169.254.137 range, generally
in addition to whatever IP address dhcp supplies. Annoyingly this
hides the "real" ip address in the output
of route, althogh ip addr list will show both.
Since you really only need this as a fallback for as-hoc
networks that lack a DHCP server, I edited /etc/default/zeroconf and
enabled the option that makes it only assign an address as a fallback if
dhcp does not provide one. I don't really understand why this is not the
default.
Next I installed libnss-mdns. This allows looking up hostnames in the
.local domain, which will be resolved via multicast dns over the zeroconf
network of local machines. To make it work /etc/nsswitch.conf needs to be
edited to have this line:
hosts: files dns mdns
I filed bugs on the [lack of documentation about that, and also on base-files to possibly get it supported by default w/o manual editing, which we'll need if we want regular users to use this.
Finally, if you want your machine to have a .local hostname in mDNS, you
need a responder to broadcast it. One such is in the mdnsresponder, which
unfortuatly has an unresolved license mess that has been pending resolution
for too long. It also seems to be the only package in Debian to perform
this task, so I used it anyway. :-( It's rather lacking in documentation
and it took me a while to work out that I didn't really need to edit its
config file, since it defaults to broadcasting your hostname.
Now I could ping dragon.local; if I had two hosts they should automatically network together with no configuration.
Of course to make this really useful you need a way to discover services
on the network, and mdns-scan is one way to do this easily. The
howl-utils can be used to look for specific services and to publish a
service. But they have no useful docs in Debian, not even man pages,
so see this page
for some usage hints.
Of the other zeroconf stuff in Debian, daapd looked useless unless you
have iTunes, and I couldn't find anything else, aside from probably gnome
and kde GUI stuff.
Finally, I've been thinking about whether it would make any sense to install any of this stuff by default in Debian as part of the laptop task or some other task. Installing libnss-mdns seems like a reasonable thing to do, once it works with no configuration. mdnsresponder would also be fine to install, if it remains in Debian. zeroconf might be ok to include as well, unless its behavior of hiding real IP addresses is too annoying.
To be useful as a server on a zeroconf network, Debian should publish running services, possibly integrated with init scripts somehow, but I don't know what would be a good way to do that.