mDNS Bridge

The mDNS Bridge package (FreeSense-pkg-mDNS-Bridge 2.2) runs the mdns-bridge daemon (version 2.2.0 or later, from the FreeBSD package repository). It forwards Multicast DNS (mDNS) packets between two or more interfaces, so DNS Service Discovery works across network segments: printers, AirPlay and Chromecast devices, home automation hubs and similar services become visible on other VLANs.

mDNS Bridge only forwards and filters mDNS. It does not publish records for the firewall. If you also need publishing, use Avahi instead. The two packages must not reflect mDNS at the same time, and each refuses to save while the other is active.

Install

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

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

Where to find it

Services → mDNS Bridge (in the Network group of the Services menu), page mdns-bridge.php. The page has General Settings, Global Settings, one settings section per eligible interface (for example LAN Settings), and Advanced.

First-time setup

Open Services → mDNS Bridge.
Check Enable.
In Interfaces, select at least two interfaces, for example LAN and IOT. Interfaces that have a gateway (WAN-type interfaces) are not offered.
Leave IP Protocols on IPv4 and IPv6 unless one family is not used.
Optional: to reflect only some services, set Global Filter to Allow and enter service names in Global Filter List, for example _ipp, _airplay, _googlecast.
Click Save. The daemon is restarted with the new configuration.
Add firewall rules for mDNS on each selected interface (see below) and test discovery from a client.

Settings reference

General Settings

Field	What it does	Default
Enable	Runs the daemon. When unchecked, the daemon is stopped and its config and rc files are removed.	Off
CARP Status VHID	In an HA pair, the daemon runs only while the selected VHID is MASTER.	`none`
Interfaces	Interfaces the daemon operates on. At least two are required. Interfaces with a gateway are excluded from the list.	None
Decode Warnings	Log mDNS decoding errors that are silent by default (`-w`).	Off

Global Settings

Field	What it does	Default
IP Protocols	IPv4 and IPv6, IPv4 only or IPv6 only. A global choice overrides the per-interface setting.	IPv4 and IPv6
Global Filter	Filter applied to incoming packets on all interfaces before any interface filter. none allows all names; Allow drops names not in the list; Deny drops names in the list.	none
Global Filter List	Comma-separated mDNS names, usually single service labels such as `_printer`, `_ipp`, `_ipps`, `_airplay`, `_hap`, `_http` or `_ssh`.	Empty

Per-interface settings

Each eligible interface has its own section. The settings apply only when the interface is selected in Interfaces.

Field	What it does	Default
IP Protocols	Protocol family for this interface. Ignored when a global protocol limit is set.	IPv4 and IPv6
Inbound Filter	Applied to packets received on this interface, after the global filter: none, Allow or Deny.	none
Inbound Filter List	Names for the inbound filter.	Empty
Outbound Filter	Applied before packets are sent out on this interface: none, Allow or Deny.	none
Outbound Filter List	Names for the outbound filter.	Empty

Every filter list entry must be a valid domain label; invalid entries are rejected on save.

Advanced

Field	What it does	Default
Disable Packet Filtering	Forwards packets between interfaces without decoding or validating them. This disables all mDNS validation and filtering, including link-local address checks. Only takes effect when no filters are set. Use with extreme caution.	Off

Firewall rules and interfaces

mDNS uses UDP port 5353 to 224.0.0.251 (IPv4) and ff02::fb (IPv6).
The package adds no firewall rules. On each selected interface, allow UDP from the interface network to destination port 5353.
Add rules for the service traffic itself (printing, casting, control ports) between the networks. Discovery alone does not let clients connect.
Use filters to keep the bridge narrow. For example, allow only _ipp and _ipps from a printer VLAN, rather than every service from every segment.

Service, logs, and status

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

Upgrade, backup, and removal

Settings are stored in config.xml under installedpackages/mdns-bridge and 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
Save fails with Avahi reflection must be disabled before enabling mDNS Bridge	Avahi is enabled with reflection. Turn off Avahi reflection or use Avahi instead.
Save fails with A minimum of two interfaces are required	Select two or more interfaces.
An interface is missing from the list	It has a gateway configured, so it is treated as a WAN and excluded.
Invalid domain in … Filter List	An entry contains characters that are not valid in a DNS label. Use names such as `_ipp`.
Services are not discovered	Check the UDP 5353 rules, the filters (set them to none while testing) and that the service is running on Status → Services. Enable Decode Warnings to log malformed packets.
The daemon does not run on the HA backup	Expected with CARP Status VHID set; it starts when the VHID becomes MASTER.