Configuring Broadcast Packet Handling Perform the tasks in these sections to enable these schemes: • Enabling Directed Broadcast-to-Physical Broadcast Translation • Forwarding UDP Broadcast Packets and Protocols • Establishing an IP Broadcast Address • Flooding IP Broadcasts Enabling Directed Broadcast-to-Physical Broadcast Translation By default, IP directed broadcasts are dropped; they are not forwarded. Dropping IP-directed broadcasts makes routers less susceptible to denial-of-service attacks. You can enable forwarding of IP-directed broadcasts on an interface where the broadcast becomes a physical (MAC-layer) broadcast.
Only those protocols configured by using the ip forward-protocol global configuration command are forwarded. You can specify an access list to control which broadcasts are forwarded. When an access list is specified, only those IP packets permitted by the access list are eligible to be translated from directed broadcasts to physical broadcasts. For more information on access lists, see the “Configuring ACLs" chapter in the Security Configuration Guide . Note The ip network-broadcast command must be configured at the ingress interface before configuring the ip directed-broadcast command at the egress interface.
This ensures that the IP-directed broadcasts work correctly and prevents an outage from occurring after an upgrade. Configuring IP Unicast Routing Configuring Broadcast Packet Handling Command or Action Purpose Step 11 end Example: Device(config)#end Returns to privileged EXEC mode. Step 12 show ip irdp Example: Device#show ip irdp Verifies settings by displaying IRDP values. Step 13 copy running-config startup-config Example: Device#copy running-config startup-config (Optional) Saves your entries in the configuration file. Configuring IP Unicast Routing 22