Routing

The Linux OS decides where the output stream will be sent or correctly said routed. The behavior of this is defined in the routing table. You can check the current routing table with

ip route

and you will receive something like this (this depends on your network configuration):

default via 172.30.1.1 dev enp0s3 proto dhcp src 172.30.1.87 metric 100
172.30.1.0/24 dev enp0s3 proto kernel scope link src 172.30.1.87 metric 100
192.168.56.0/24 dev enp0s8 proto kernel scope link src 192.168.56.124

In this case there are 2 interfaces enp0s3 and enp0s8. The first is the default.

By running

sudo ip route add 224.0.0.0/4 dev enp0s8

all multicast traffic will be sent to interface enp0s3. This is shown in the updated routing table:

default via 172.30.1.1 dev enp0s3 proto dhcp src 172.30.1.87 metric 100
172.30.1.0/24 dev enp0s3 proto kernel scope link src 172.30.1.87 metric 100
192.168.56.0/24 dev enp0s8 proto kernel scope link src 192.168.56.124
224.0.0.0/4 dev enp0s8 scope link

The changes to the routing table will be active only until restart of the system. To make them permanent you have to write them to /etc/network/interfaces or /etc/netplan/50-clou-init.yaml depending on your OS.

Documentation

Routing