Multicast: Difference between revisions

<strong>Unofficially and completely at own risk</strong>, it has been found to be possible to watch the [https://community.bt.com/t5/YouView-Boxes/IPC6023-Advanced-Diagnosis/td-p/1154880 Test Channel] as described on the BT website, on an AAISP provided FTTC line. This is [https://community.bt.com/t5/YouView-from-BT/Multicast-Test-Channel-URL/td-p/2223426 updated as of 2022]

As a workaround to IPv4 not customarily allowing ifindex or interface name specification in addresses, (known as scope or "%", in IPv6) route to the multicast group on the device upon which PPPoE runs, aimed at the openreach modem:

echo ip route add 234.81.131.194 dev $DEVICE

ffplay rtp://234.81.131.194:5802

vlc rtp://234.81.131.194:5802

It may happen that the computer hosting PPPoE is in an inconvenient location for watching and that other networked devices should receive copies of the stream. [http://troglobit.github.io/smcroute smcroute] lets one forward multicast statically at first and can even work where programs do not understand IGMP or in some situations even multicast, which can be aided with DNAT rules and/or use of -j REDIRECT on targets

It may be possible later to have other programs listen for IGMP/MLD and then "manage" smcroute, due to a possible linux limitation of only allowing one userspace program manage kernel mrouting at a time, to have maximum flexibility in upstreams and downstreams including internal sources.

Other software that may be useful is [https://manpages.debian.org/stable/igmpproxy igmpproxy] and [https://unfix.org/projects/ecmh/ ecmh]

For testing and usage, smcroute can reflect the multicast to other attached networks. The smcroute 2.4.4 as found in Debian 11, would not configure the interface without an IP address on it, however the very latest smcroute allows 0.0.0.0 to be used to originate the IGMP3 joins, this needed the upgrade from ip_mreq to ip_mreqn in the smcroute code.

Additionally the sysctl rp_filter is disabled on $DEVICE and "all" to allow the incoming multicast without a matching outgoing route, also desirable. iptables and/or nftables would still be used to filter.

smcroute requires the source address, this was found with wireshark or tcpdump, and could be subject to change, <var>int0</var> and <var>ext0</var> are example devices to copy multicast packets to, these could be internal vlans on a home network:

smcroutectl add $DEVICE 109.159.247.194 234.81.131.194 <var>int0 ext0</var>

smcroutectl add $DEVICE 109.159.247.200 234.81.131.200 <var>int0 ext0</var>

smcroutectl add $DEVICE 109.159.247.216 234.81.132.216 <var>int0 ext0</var>

To actually start, substituting for the other addresses beginning 234. above for the other channels.

smcroutectl join $DEVICE 234.81.131.194

smcroutectl leave $DEVICE 234.81.131.194

now ffmpeg, vlc or other client can be ran elsewhere on the internal network, if their ethernet interfaces do not have legacy ip addresses and the client does allow specification of an interface for IGMP, which is more usual with ipv6, a workaround is <code>ip route add 234.81.131.194/32</code> on these devices with a device aiming towards the PPPoE host system.

* [https://www.bt.com/about/sinet BT] and [https://www.openreach.co.uk/cpportal/help/suppliers-information-notes-(sins) openreach] supplier information notes, especially BT 511 and openreach 503