[avahi] Link local IPV6 addresses

Lennart Poettering lennart at poettering.net
Mon Feb 5 09:25:47 PST 2007

On Mon, 05.02.07 09:17, Alexander Larsson (alexl at redhat.com) wrote:

> > This wouldn't work. Unfortunately most applications first query for
> > IPv6 hostnames and then for IPv4 hostnames. i.e. the order which
> > address we return first is not specified by us, but depends on the
> > application.
> Well. Such applications would still have problems. However it would be
> nice if there was a easy way to fix them. (I.E. let you specify "I
> handle both ipv6 and ipv4, give me the 'best' version".)

The problem is glibc's gethostbyname2(). It expects an address family
argument, which may be either AF_INET or AF_INET6, but unfortunately
not AF_UNSPEC. On Linux NSS modules such as libnss-mdns provide an
implementation for gethostbyname2().

getaddrinfo() would be a solution here. However, AFAIK NSS modules may
not provide an implementation for that function, instead it is
emulated on top of gethostbyname2().

> > Isn't it possible to set a proper IPv6 route for the link-local block and
> > thus allowing usage of those addresses even without specifying the
> > interface on connect()? That way IPv6 link-local addresses would
> > behave much the same way as IPv4 link-local addresses. -- if this is
> > is not possible with current Linux kernels, then maybe it's time to fix
> > the kernel. Otherwise people will never start to use IPv6 link-local
> > addresses for anything useful.
> This isn't only a problem with connect(). For instance, I first found
> this in gnome-user-share where we look for exposed dav shares and
> construct a URI from them. However, there is no way to create a URI for
> a link-local ipv6 address (as you can't put the interface in it), and
> even if you do using the ipv4 address would be better (unless it was
> also link-local) because then you could hand the uri to another machine
> and it would resolve.

Redhat has a few kernel developers employed, hasn't it? Maybe you can
ping your fellow colleagues and ask them what could be done to make
link-local IPv6 addresses more usable! ;-)


Lennart Poettering; lennart [at] poettering [dot] net
ICQ# 11060553; GPG 0x1A015CC4; http://0pointer.net/lennart/

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