[avahi] Ipv6 turned off in default config

Lennart Poettering lennart at poettering.de
Wed Nov 23 15:07:56 PST 2005

On Mon, 21.11.05 13:58, Sjoerd Simons (sjoerd at luon.net) wrote:

> Hi,
> I was wondering why use-ipv6=no in the default avahi-daemon.conf. Is
> there some problem when ipv6 is enabled ?

Yes, there is. If both IPv6 and IPv4 are enabled all services will be
published via *both* protocols. This has the side effect that all
services will show up twice when the user browses for them. Once they
are discovered via IPv4 and once via IPv6. In Apple's version of the
DNS-SD spec there is no algorithm defined to check whether two
services are identical, so we must assume that the service found on
IPv4 is actually different from the one found via IPv6.

To deal with this we added a special "service cookie" feature to
Avahi. If enabled (which it is by default) a random cookie is attached
to every service published. Two services with the same name, type and
cookie can be assumed to be identical, regardless of the protocol or
the interface they were found on.

However until now there are not that many apps that make use of the
service cookie feature and this is still a feature specific to
Avahi. Marc Krochmal showed some interest in adopting some stuff like
this in the official spec, but i haven't heard anything from him
regarding this recently.

Besides the issue described above enabling both protocols at the same
time will probably double your network traffic too.

Since most peole still run an IPv4-only network we decided to disable
IPv6 by default.

(A side noe: MacOSX doesn't enable both IPv4 and IPv6 in DNS-SD
simultaneously either.)


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

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