If you are using Moblock, and also trying to enable service discovery on your linux machine with Avahi, you probably need to unblock “24.0.0.0/24″. It solved my problems…
That’s all 
Basically, if you watch you will see your machine trying to make outbound connections to an IP like 24.0.0.22, probably on port 5353. This isn’t a virus or malware, this is multicast, and its OK.