This project is part of a larger effort called TreeDN. The goal of TreeDN is to bring content that relies on multicast infrastructure to users in networks that do not support multicast. The key idea is to automatically translate unicast traffic to multicast traffic as the traffic enters a multicast-enabled network from a unicast-only network, and vice versa when the traffic enters a unicast-only network from a multicast-enabled network. So far, the latter (multicast to unicast translation) has been achieved using Automatic Multicast Tunneling (AMT), which, as the name suggests, essentially tunnels multicast traffic by wrapping it in unicast packets when the traffic leaves the multicast-enabled network, such that the traffic can travel across the unicast-only network and ultimately be unwrapped by the receiving end host.
While AMT allows for delivery of content originating from (and sent as multicast) a host in a multicast-enabled network (e.g., the Multicast Backbone (MBONE)) to receivers in unicast-only networks, it does not provide unicast-to-multicast translation, as stated in the February 2015 revision of the RFC:
This document does not describe any methods for sourcing multicast traffic from isolated sites, as this topic is out of scope.
A different solution is therefore needed to enable a host in a unicast-only network to source content intended for multiple recipients in multicast-enabled networks (and/or in unicast-only networks where there is a multicast-enabled transit network with AMT support between the source and the receiver). The goal of this project is to develop a service that performs unicast-to-multicast translation to enable such unicast-only sources to utilize the multicast capabilities of the (transit) multicast-enabled networks between the source and its receivers.
The unicast-to-multicast translator uses a socket-based design. The translator maintains two sockets:
- a regular (UDP) unicast socket Su to which the unicast-only source sends its unicast traffic;
- and a multicast (UDP) socket Sm on which the payload of the inbound unicast packets are sent out as multicast packets.
Whenever a unicast packet p arrives at Su, the translator determines if it has already received prior packets from the same unicast source s by looking up s (identified by the source IP and source port of p) in a dictionary d that maps unicast sources to their assigned multicast addresses (groups). If there is an entry for s in d, the translator simply sends the payload of p out on Sm, specifying the multicast address pointed to by s in d as the destination IP address. If there is currently no entry for s in d, the reception of p indicates the start of a new unicast flow that is to be translated. In this case, the translator randomly selects a multicast address (group) m from its (configurable) multicast address space and inserts an entry in d that maps s to m. It then sends the payload of p out on Sm, specifying m as the destination IP address.
The primary benefit of this design is that all network and transport layer headers are automatically stripped (in the case of inbound traffic) and generated (in the case of outbound traffic) by the operating system's networking stack. Furthermore, since Su is a UDP socket, there is no need for multithreading as the main thread can serve multiple clients concurrently by constantly polling a single socket (Su) as all clients send data to this single socket (as opposed to TCP, where there is one socket per connection).
The code is written in Python 3. We have successfully deployed the translator in our test environment using Python v3.7.3 and 3.11.2.
The code relies on the following third-party libraries:
The default configuration should suffice for most use cases, so simply do:
$ python3 translator.py
Press CTRL+C to stop translator
read timeout: nothing to be translated this iteration
read timeout: nothing to be translated this iteration
...
Multicast address (232.74.37.48, 9002) allocated for ('66.129.239.15', 31380).
Added amt://[email protected]:9002 to the Multicast Menu ([email protected]; description=Translated stream originating from 66.129.239.15).
Once the translator is running, you can terminate it by pressing CTRL+C. The translator will report a read timeout at periodic intervals (currently set to 5 seconds) as long as it is not receiving any unicast packets for translation. This is not an error, but rather an indication that the translator is alive and well and simply waiting for clients to start sending unicast packets to the translator.
Whenever a packet pertaining to a previously unseen unicast flow arrives (a packet is mapped to its respective flow using its source IP and its source port), the translator will randomly pick a multicast address and reserve it for that new flow. This initial unicast packet, and any subsequent unicast packets pertaining to that same flow, will then be translated to multicast packets with a destination IP matching the multicast address that was reserved for the unicast flow. The translator will also add information about the new stream to the Multicast Menu. An example of what these entries will look like is provided in the screenshot below.
An example of running translator as a secured service is available here.
A set of CLI options are available if you want to configure what IP address to listen for unicast flows on, what multicast address space to randomly pick multicast addresses from (when assigning a multicast address to a new unicast flow) etc. Refer to the CLI help:
$ python3 translator.py --help
usage: translator.py [-h] [--unicast-nif-ip UNICAST_NIF_IP]
[--unicast-port UNICAST_PORT]
[--multicast-addr-space MULTICAST_ADDR_SPACE]
[--multicast-port MULTICAST_PORT]
Start a unicast-to-multicast translation service on this machine.
optional arguments:
-h, --help show this help message and exit
--unicast-nif-ip UNICAST_NIF_IP
IP address of the network interface to listen for
unicast on. The default value is what was determined
to be the primary network interface of this machine
(i.e., the network interface that has a default
route). Note that this address may not be a public
address if this machine is behind NAT or a VPN.
Default: 162.250.138.11
--unicast-port UNICAST_PORT
Port number to listen for unicast on. Default: 9001
--multicast-addr-space MULTICAST_ADDR_SPACE
Address space to (randomly) pick destination multicast
addresses (groups) from for the translated unicast
flows. Default: 232.0.0.0/8
--multicast-port MULTICAST_PORT
Port number to use as the destination port when
forwarding unicast flows as multicast flows. The same
port number will be used for all translated flows.
Thus, a translated flow is identified solely by its
assigned multicast IP address (group). Default: 9002
Note that the default value for --unicast-nif-ip is determined dynamically so python3 translator.py --help will
report a different default value for this option on your machine.
To get involved, contact Lenny Giuliano ([email protected]) or Andrew Gallo ([email protected]) to be added to the MTTG Slack Group.