How to forward IP packets destined for a Layer 3 broadcast address

This article provides configuration information to forward IP packets destined for a Layer 3 broadcast address.

In the following example, when an IP packet addressed as 10.10.10.255 is sent from the corporate network 192.168.1.0/24, the packets are dropped at the firewall located at the remote office. The intent is to send broadcast addresses addressed to a remote network from corporate network to detect hosts/machines located in a remote office.

Targeted Broadcast Diagram

By default, the router/firewall does not forward the IP packets destined for a Layer 3 broadcast address, as it is designed to break broadcast domain.

To forward IP packets destined for Layer 3 broadcast address, it is necessary to configure the targeted broadcast to an egress interface and/or routing engine.

Perform the following configuration to enable targeted broadcast:

1. Configure the physical interface:

   [edit]
   user@host# edit interfaces interface-name

2. Configure the logical unit number:

   edit interfaces interface-name]
   user@host# edit unit logical-unit-number

3. Configure the protocol family inet:

   [edit interfaces interface-name unit logical-unit-number]
   user@host# edit family inet 
   

4. Configure targeted broadcast:

   [edit interfaces interface-name unit logical-unit-number family inet]
   user@host# edit targeted-broadcast

5. Specify one of the following options:

• To send packets to the egress interface and to the Routing Engine:

  [edit interfaces interface-name unit logical-unit-number family inet targeted-broadcast]
  user@host# set forward-and-send-to-re

• To send packets to only the egress interface:

  [edit interfaces interface-name unit logical-unit-number family inet targeted-broadcast]
  user@host# set forward-only

This is not a supported feature in high-end SRX series of devices.