Multicast Bridge

The Multicast Bridge package (FreeSense-pkg-mcast-bridge 1.4) runs the mcast-bridge daemon (version 1.3.0 or later, from the FreeBSD package repository). It forwards UDP multicast traffic for chosen groups and ports between interfaces, for both IPv4 and IPv6. Typical uses are IPTV or audio streams, multicast-based discovery for specific applications, and sensors that publish to a multicast group on another VLAN.

Each forwarding rule is a bridge: one UDP port, one IPv4 and/or IPv6 multicast group, a set of inbound interfaces and a set of outbound interfaces. By default the bridge uses IGMP (IPv4) and MLD (IPv6) to forward only to interfaces that have an active subscriber.

For mDNS (UDP 5353, 224.0.0.251) use mDNS Bridge or Avahi instead: link-local groups cannot be bridged by this package. For broadcast-based protocols use UDP Broadcast Relay.

Install

Open System → Package Manager → Available Packages.
Find Multicast Bridge (package FreeSense-pkg-mcast-bridge) and click Install.

On Stable 1.1 the package is available for amd64. See Installing packages.

Where to find it

Services → Multicast Bridge (in the Routing group of the Services menu):

mcast_bridge.php: the Settings section and the Bridges table (UDP Port, IPv4 Address, IPv6 Address, Inbound Interfaces, Outbound Interfaces, Description). Static interfaces are marked with an asterisk.
mcast_bridge_edit.php: Edit Bridge, opened with Add or the edit icon.

First-time setup

Open Services → Multicast Bridge.
Click Add under Bridges.
Enter the UDP Port of the stream, for example 5004.
Enter the IPv4 Multicast Address, for example 239.1.1.10, and/or an IPv6 group.
Select the Inbound Interfaces where the source sends, for example IPTV.
Select the Outbound Interfaces where receivers are, for example LAN.
Add a Description and click Save.
Back on the main page, check Enable and click Save.
Click Apply Changes in the banner. Changes are not applied until you do.
Add the firewall rules described below, then start a receiver on the outbound network.

Settings reference

Settings (main page)

Field	What it does	Default
Enable	Runs the daemon. It only starts when at least one bridge is enabled.	Off
CARP Status VHID	In an HA pair, run only while the selected VHID is MASTER.	`none`
IGMP Querier Mode	When the bridge acts as IGMP querier (IPv4): Never, Quick (at startup), Delay (after 125 seconds if no other querier is present) or Defer (delay and always defer to other queriers).	Quick
MLD Querier Mode	The same choice for MLD (IPv6).	Quick

Most networks have a switch or router acting as querier. Use Delay or Defer when another querier exists, so they do not compete.

Edit Bridge

Field	What it does	Default
Disable	Keep the bridge in the configuration but do not run it.	Off
UDP Port	Destination UDP port of the stream. Required, and unique across bridges.	Empty
IPv4 Multicast Address	IPv4 group to forward. Must be routable; groups in `224.0.0.0/24` are refused.	Empty
IPv6 Multicast Address	IPv6 group to forward. Must be routable; groups in `ff02::/16` are refused. At least one of the two addresses is required.	Empty
Inbound Interfaces	Interfaces the bridge receives from. It joins the group there only while a subscriber exists on an outbound interface.	None
Static Inbound Interfaces	Inbound interfaces where the bridge joins the group at startup and never leaves.	None
Outbound Interfaces	Interfaces the bridge forwards to, only while IGMP/MLD shows an active subscriber.	None
Static Outbound Interfaces	Interfaces that always receive the stream; IGMP/MLD is not used there.	None
Description	Free text for reference.	Empty

At least one inbound and one outbound interface (normal or static) are required. An interface can appear in both lists to make the bridge bidirectional, but a bridge with only one inbound interface cannot use that same interface as its only outbound interface, and the reverse.

The main page also lets you toggle a bridge on or off and delete it. Each change asks you to Apply Changes.

Firewall rules and interfaces

The package adds no firewall rules.

On each inbound interface, allow UDP from the source to the multicast group and port of the bridge, for example destination 239.1.1.10 port 5004.
On each outbound interface where IGMP or MLD is used, receivers send membership reports. IGMP packets carry an IP option (Router Alert), which the firewall blocks by default. Add a pass rule for protocol IGMP and enable Allow IP options in the rule’s advanced options.
Static interfaces do not need IGMP/MLD rules.

See Firewall rules and aliases.

Service, logs, and status

Item	Value
Service name	`mcast-bridge` (Multicast Bridge in Status → Services)
rc script	`/usr/local/etc/rc.d/mcast-bridge.sh`
Configuration file	`/usr/local/etc/mcast-bridge.conf` (generated, do not edit)
PID file	`/var/run/mcast-bridge.pid`
Logs	The daemon logs to syslog (`-s`); messages appear in Status → System Logs → System → General.

Upgrade, backup, and removal

Settings are stored in config.xml under installedpackages/mcast-bridge and are included in configuration backups.
Removing the package stops the daemon and deletes its config and rc files. The settings stay in config.xml for a later reinstall.

Troubleshooting

Symptom	Cause and fix
IPv4 Multicast Address is link local (non routable)	Groups in `224.0.0.0/24` (and `ff02::/16` for IPv6) cannot be bridged. Use mDNS Bridge or UDP Broadcast Relay for link-local protocols.
UDP Port is already in use by another bridge instance	Each bridge needs a unique port. Combine the groups on that port into one bridge.
The service does not start	Enable is off, every bridge is disabled, or the changes were not applied. Click Apply Changes.
The stream reaches the firewall but not the receivers	IGMP reports are blocked. Add the IGMP rule with Allow IP options, or make the outbound interface static.
The stream stops after a few minutes	No querier is active, so memberships time out. Set IGMP Querier Mode / MLD Querier Mode to Quick, or enable a querier on the switch.