[RFE] Add multicast parameters to bridge settings

[Pedro Guimarães]

Netplan should be able to support setting multicast parameters using: https://netplan.io/reference/#properties-for-device-type-bridges

These parameters can be found on /sys for a given bridge:
https://pastebin.ubuntu.com/p/krBy2SHhM7/

The most relevant ones being:
multicast_querier
multicast_router
multicast_snooping
multicast_igmp_version
multicast_querier_interval
multicast_query_interval

Which allow to configure multicast snooping onto the bridge.

[Pedro Guimarães (pguimaraes)]

There was also a bug a couple of years ago, which I did not try to reproduce yet, but is also relevant or getting multicast support:
https://bugs.launchpad.net/netplan/+bug/1833475

[David Baird (dhbaird)]

This workaround seems to do what I want, but this is a new way of doing things so I'm not totally sure this is ideal. It relies on identifying bridges by interface names ending in "br":

mkdir -p /etc/networkd-dispatcher/configuring.d
install -C -m 0755 /dev/stdin /etc/networkd-dispatcher/configuring.d/50-br-multicast << 'EOF'
#!/bin/bash
if [[ "$IFACE" =~ .*br ]]; then
    echo -n 3 > /sys/class/net/$IFACE/bridge/multicast_igmp_version # default: 2
    echo -n 2 > /sys/class/net/$IFACE/bridge/multicast_mld_version # default: 1
    echo -n 1 > /sys/class/net/$IFACE/bridge/multicast_querier # default: 0
    echo -n 1 > /sys/class/net/$IFACE/bridge/multicast_snooping # default: 1
fi
EOF