alsmith / Multicast Relay

Relay broadcast and multicast packets between interfaces

Useful, for example, if you have Sonos speakers on one interface, or VLAN, and you want to be able to control them from devices on a different interface/VLAN. Similar for Chromecast devices.

By default, SSDP multicast packets received on 239.255.255.250:1900 are relayed to the other interfaces listed, as well as multicast DNS packets received on 224.0.0.251:5353.

Broadcast UDP packets received on port 6969 are also relayed by default: this is used by Sonos during the initial device-discovery phase, initiated by pressing either the infinity button or the play+volume up buttons, depending on your Sonos speaker.

Please note that even when your devices have discovered one another, at least in the Sonos case, a unicast connection will be established from the speakers back to the controlling-telephone. You will need to make sure that IP forwarding is enabled (echo 1 > /proc/sys/net/ipv4/ip_forward) and that no firewalling is in place that would prevent connections being established.

usage: multicast-relay.py [-h] --interfaces INTERFACE INTERFACE [INTERFACE ...] [--noTransmitInterfaces INTERFACE ...] [-ifFilter IFFILTER] [--relay BROADCAST_OR_MULTICAST:PORT [BROADCAST_OR_MULTICAST:PORT ...]] [--noMDNS] [--noSSDP] [--noSonosDiscovery] [--oneInterface] [--homebrewNetifaces] [--wait] [--listen REMOTE_ADDRESS [REMOTE_ADDRESS ...]] [--remote REMOTE_ADDRESS] [--remotePort PORT] [--remoteRetry SECS] [--foreground] [--logfile FILE] [--verbose]

--interfaces specifies the >= 2 interfaces that you desire to listen to and relay between. You can specify an interface by name, by IP address, or by network/netmask combination (e.g. 10.0.0.0/24 in the last case). With certain flags below, the minimum number of interfaces drops to >= 1.

--noTransmitInterfaces specifies interface(s) that are listen-only.

--ifFilter specifies a JSON file where one can state that a source address A.B.C.D/M is only to be relayed to specific interfaces. This can be useful in applications such as a hotel where relaying for one guest room may only discover device(s) that are in the same guest room. See example file ifFilter.json.

--relay specifies additional broadcast or multicast addresses to relay.

--noMDNS disables mDNS relaying.

--noSSDP disables SSDP relaying.

--noSonosDiscovery disables broadcast udp/6969 relaying.

--oneInterface support for one interface connected to two networks. Use with caution - watch out for packet storms (although the IP checksum list ought to still prevent such a thing from happening).

--homebrewNetifaces attempt to use our own netifaces implementation, probably doesn't work on any other system than Linux but maybe useful for OpenWRT where it's rather tricky to compile up netifaces.

--allowNonEther supports non-ethernet interfaces to be relayed [experimental].

--wait indicates that the relay should wait for an IPv4 address to be assigned to each interface rather than bailing immediately if an interface is yet to be assigned an address.

--listen for connections from the specified remote host(s).

--remote connect to the specified remote host. If either --listen or --remote are specified, then one can also specify just one local interface with --interfaces.

--remotePort use the specified port for remote communications (default: 1900).

--remoteRetry if the remote connection fails, wait at least this number of seconds before retrying (default: 5).

--aes use the specified string to encrypt/decrypt data packets.

--foreground stops the process forking itself off into the background. This flag also encourages logging to stdout as well as to the syslog.

--logfile saves log data to the specified file.

--verbose steps up the logging.

multicast-relay.py requires the python 'netifaces' package. Install via 'easy_install netifaces' or 'pip install netifaces'. For ZeroShell users, please review README-ZeroShell for further instructions.

Al Smith [email protected]