Comment 10 for bug 624043

Hi All, Trent Lloyd here - one of the authors of the Avahi project

The cause of this situation is relatively simple, in all cases I have seen it is caused by a faulty network driver. You will find after you restart Avahi - services work for a few minutes and then they fail again - here is the cause

 => When Avahi starts, it broadcasts out to the network services exists
 => Machines discover the service and add it to the list of available services
 => Once it nears the expiry time, a query is sent out for the services
 => No response is received, because multicast functionality in the network card driver is broken.. multicast queries never reach the avahi daemon
 => Avahi detects this as a "Passive observation of failure" and removes the services from the service list (Mac OS X Bonjour does the same)

The fix is to get a different network card with a working driver support for multicast - or fix the network card driver - it would be useful to post your "lspci" outputs to the issue to identify what kind of network cards you have and mention which one it is (ethernet or wireless)

Is most common on wireless but does occur on some ethernet drivers as well.