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To receive a multicast on my not default NIC (dvb) I do the following:
at this point the only way to receive the needed multicast packets is to add in the routing table a rule to reach the network where the sender is (another network) trough the dvb, as if the dvb needs to reply to the multicast sender; let say a sort of source sender multicast mode. Anyone knows what is going on? The problem is annoying to me because in principle I don't know the ip of sender.
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A multicast packet is a network packet meant to be received by more than one host, but not by all hosts. This functionality is obtained by assigning special hardware addresses to groups of hosts. Packets directed to one of the special addresses should be received by all the hosts in that group.
To join a multicast group, a host sends a join message, using the Internet Group Management Protocol (IGMP), to its first-hop router. Groups are identified by a single class D IP address (in the range 224.0. 0.0 to 239.255. 255.255).
Netplan lacks an option to add multicast routes. To route multicast out of the ens7 interface, you would add a route to 224.0. 0.0/4 tied to the Ethernet device you want to use. This is not possible with netplan; it is just missing the option to add multicast routes, i.e. with a device instead of a gateway.
You appear to be being stung by rp_filter reverse-path filtering. This drops packets if they arrive on an interface that doesn't have a route for the source address.
You can disable it on a per-interface basis with the sysctl /proc/sys/net/ipv4/conf/<if>/rp_filter.
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