OsmocomBB

I am using a virual-um setup on my laptop for osmocom development and testing without additional hardware.

In this situation I do not want virtphy's traffic leaking to the local network,
however the traffic currently leaks.

As a workaround, virtphy could be run in a separate network namespace or a virtual machine.
But this issue seeks a solution which works without resorting to a separate network stack.

Blocking the traffic with iptables leads to errors on virtphy's socket, and adding a route to 224/4 via lo does
not have the desired effect as multicast traffic is still routed towards the default route.

Possible solutions:
Harald suggested trying to set the TTL of multicast packets to 0, and there's also the IP_MULTICAST_IF socket option
which could be used to bind virtphy to a specific interface.