Allow avahi to bind to selected network interfaces instead of all MULTICAST, non-P2P

[dkg]

It would be nice if avahi could be configured to only bind to selected interfaces.

This has been brought up before as a requested feature, but i figured it would make sense to have a ticket to track the feature, so the priority/assignment/plan for it is documented.

FAQ 10 addresses this point with a workaround of turning off MULTICAST for the interfaces that are not desired, but this fails to address the scenario where an administrator wants MULTICAST capabilities on an interface, but does not want avahi bound to it.

Thanks for avahi!

[dkg]

Another corner case related to this is if mDNS is desired on multiple interfaces, but certain zones should be collaboratively managed only on specific interfaces

An example use case: Server A has three interfaces, on which multicast DNS/DNS-SD might be relevant. However, the .trusted TLD should only be resolvable/shared over eth0 (i.e. broadcasts of .trusted RRs from other interfaces should be ignored), while .dmz should be resolvable/shared over eth1, and .local should be handled over both interfaces. No multicast DNS or DNS-SD should be performed at all over eth2.

I don't know the protocols well enough to know if this would even be possible, but the scenario certainly seems plausible to me, in this era of multi-NIC'ed servers and decentralized clusters with isolated/internal network segments.

[josh]

Related issue: whenever I run a kvm virtual machine that creates a tap device, avahi starts using the tap device. I definitely do not want that; I want to put the tap devices on an isolated network, and I don't want any host service to touch the tap devices.

[lennart]

Duplicate of #212.