UDP Broadcast Relay

The UDP Broadcast Relay package listens for UDP broadcast packets and retransmits them on additional interfaces. This enables UDP broadcast discovery protocols to cross separate networks.

Important

Firewall rules are not automatically created for configured instances. If hosts on separate networks need to respond to the relayed broadcast packets, firewall rules may be needed to allow traffic back to the original sender.

General Settings

Enable

Enable the UDP Broadcast Relay service. If checked, enabled instances will be active.

Track CARP Status

Tracks the CARP status of the selected CARP VIP. The service will only run when the selected VIP is in the MASTER state.

Configured Instances

ID

The instance ID.

Port

UDP port being relayed.

Interfaces

Interfaces to relay packets on.

Description

The user-specified description.

Actions

Administrative actions available for the instance.

Edit

Edit the instance settings.

Add

Configure a new instance.

Delete

Delete the selected instance(s).

Instance Settings

Enable

Enable this instance. If unchecked, the instance will not be active.

Description

A description for administrative reference (not parsed).

Network Interfaces

Interfaces to receive and transmit packets on; must select at least two. When a packet is received, it’s sent to all specified interfaces except for the one it originated on. Unassigned and special interfaces (including lo0 and enc0) are omitted.

Note

Only interfaces with a broadcast flag and an IPv4 address are supported. Point-to-point interfaces such as those used in WireGuard are not supported.

Spoof Source

Spoof the source IP address and/or port when relaying packets.

Keep Original (default)

The source IP address and UDP port of the broadcast packet will remain unchanged.

Use Interface Address and Destination Port

Sets the source IP address to that of the outgoing interface and the source UDP port to the same as the destination port.

Use Interface Address only

Sets the source IP address to that of the outgoing interface and keeps the original source UDP port.

Instance ID

A unique number between instances (1-63). This is used to set the DSCP of outgoing packets to determine if a packet is an echo and should be discarded.

Destination Port

Destination UDP port to listen on (1-65535).

Note

Instances need to bind to the specified port on any/all interfaces. If another service such as UPnP (port 1900) or Avahi (port 5353) is running, the instance will fail to start.

Multicast Address

Multicast group to listen for and relay packets on (optional).

Examples

A list of example use cases are given below.

UDP Port	Spoof Source	Multicast Address	Description
5353	Address/Port	224.0.0.251	mDNS: used for e.g. Chromecast and Bonjour
1900	Original	239.255.255.250	SSDP: used for e.g. DLNA, Sonos, and UPnP
1900 138 137	Original Original Original	239.255.255.250 - -	Windows Network Neighborhood Discovery: uses SSDP, NetBIOS-NS, and NetBIOS-SS
21027	Original		Syncthing Discovery
19132	Original		Minecraft