[avahi] breaking avahi through vpn

[Max Kutny]

Hi Lennart,

I have several hosts on a public LAN tight together via a private VPN.
Once I got service discovery working on public LAN I chose to switch
to more secure environment and tried to setup discovery over the
private network. Unfortunately it didn't work for me.

Digging a bit I stumbled over a mail
(http://lists.freedesktop.org/archives/avahi/2005-July/000075.html)
saying that avahi treats interface with POINTOPOINT flag set as
irrelevant. Although, VPN tunnels are organized exactly with this flag
set:
7: tun0: <POINTOPOINT,MULTICAST,NOARP,UP> mtu 1500 qdisc pfifo_fast qlen 100
    link/[65534]

Manually crafting and sending UDP packet with destination
"224.0.0.251.5353" shows that it successfully gets broadcasted via VPN
tunnels.

What's the rationale behind skipping POINTOPOINT interfaces? Could it
be possible to make avahi more VPN friendly?

Thanks.

-- Max