[avahi] Strange MDNS response from Axis cameras

Marc Krochmal marc at apple.com
Thu Feb 9 21:19:12 PST 2006

On Feb 9, 2006, at 5:17 PM, Lennart Poettering wrote:

> On Tue, 07.02.06 20:26, Iván Sánchez Ortega (i.sanchez at mirame.net)  
> wrote:
>> El Martes 07 de Febrero de 2006 19:03, Marc Krochmal escribió:
>>> [...] there's still many poor customers in the world that don't  
>>> have the
>>> benefits of Zeroconf, [...] This doesn't work when you have two  
>>> cameras on
>>> the network that both use the same IP [...]
>> I can see your point. If Avahi returned the 192.168.x.x IPs for  
>> the cameras,
>> I'd be running into that problem. So the right way for Avahi to do  
>> this is,
>> as you say, to use the 169.254.x.x addresses...
> Actually, Avahi uses the first address record it gets from the  
> device, so this
> is somewhat dependant of the device logic, though this is not fully
> deterministic, due to cache management and stuff.
> BTW: Avahi itself doesn't publish link local addresses if an
> interface has both a public and an ipv4ll address assigned. So, if the
> the Axis camera would run Avahi, the problem would go away. ;-)

Except that this isn't a problem for Macs and Windows machines with  
Bonjour for Windows.  It only affects machines that don't fully  
implement RFC 3927.  We specifically asked Axis to advertise their  
link-local address in order to provide a true zeroconf out-of-the-box  
experience, since they were also constrained by their requirement to  
support non-zeroconf aware computers, by having a statically assigned  
IP address, which could potentially be on the wrong subnet,  
preventing you from communicating with it.

> I wonder if we should add some logic to always prefer real addresses
> over ipv4ll if we recieve both when browsing for them. Would make some
> sense, I guess.

Yes, for functions that can only return a single IP address, it makes  
sense to prefer the routable address, but ideally a client could use  
an API that returned all available IP addresses so it could try each  
one until it found one that succeeded.


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