Configuring Port-based LAN Broadcast Packet Forwarding

You can enable a router or switch to forward LAN broadcast traffic on only custom UDP ports to specified servers by configuring port helpers with the [edit forwarding-options helpers] port configuration statement. Port helpers are also referred to as port forwarding or UDP broadcast packet forwarding services. When you configure a port helper, the router or switch listens for incoming UDP traffic for the configured port with destination Layer 2 MAC and Layer 3 IP broadcast addresses, and forwards the packets as unicast traffic to a configured server.

Port helpers forward the traffic for configured ports transparently, without considering the application layer protocols in the packets being forwarded. However, you cannot configure a port helper to forward traffic for standard ports used by services such as BOOTP, DNS and TFTP. These services have their own explicit packet forwarding helper configuration options (see helpers and Configuring DNS and TFTP Packet Forwarding).

You can configure port helpers to listen for and forward broadcast traffic for a configured port using any of the following scopes:

• Global scope—Forward incoming broadcast traffic on the port to a configured destination server IP address.

  Configure a global port helper using only the server configuration option, without specifying a particular interface. The port helper listens for incoming traffic on any interfaces to forward to the configured server. For example:

• VLAN-specific scope—Forward incoming broadcast traffic on the port from a configured VLAN to a configured destination server IP address.

  Configure a VLAN-specific port helper using the interface statement with an IRB interface name for a VLAN, and the server statement. The port helper listens for incoming traffic from interfaces in the VLAN to forward to the configured server. For example:

• Interface-specific scope—Forward incoming broadcast traffic on the port from a configured Layer 3 interface to a configured destination server IP address.

  Configure an interface-specific port helper using the interface statement with a Layer 3 interface name, and the server statement. The port helper listens for incoming traffic only from the configured interface to forward to the configured server. For example:

For any scope, optionally use the description statement to label or describe the configured forwarding service.

In releases prior to Junos OS Release 17.2, you can configure only one destination server for a given port number. Starting in Junos OS Release 17.2R1, you can configure forwarding traffic to multiple servers for a given port in any port helper scope. To configure forwarding the traffic on a specified port to multiple destination servers, include multiple configuration items for the port and each server (or interface and server). For example, in the global scope:

To temporarily disable listening on a configured port from a configured interface, include the no-listen option with the configured item, as follows:

To remove a configured port helper service from a router or switch, delete the configured port number item, as follows:

If multiple servers are configured for a particular port, to remove any or all such forwarding services, you must delete each configured port and server item individually. For example: