Cisco Systems 3130 User Manual
38-15
Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
OL-13270-01
Chapter 38 Configuring IP Unicast Routing
Configuring IP Addressing
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.
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.
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
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
Beginning in privileged EXEC mode, follow these steps to enable forwarding of IP-directed broadcasts
on an interface:
on an interface:
Use the no ip directed-broadcast interface configuration command to disable translation of directed
broadcast to physical broadcasts. Use the no ip forward-protocol global configuration command to
remove a protocol or port.
broadcast to physical broadcasts. Use the no ip forward-protocol global configuration command to
remove a protocol or port.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Enter interface configuration mode, and specify the interface to
configure.
configure.
Step 3
ip directed-broadcast [access-list-number]
Enable directed broadcast-to-physical broadcast translation on the
interface. You can include an access list to control which broadcasts
are forwarded. When an access list, only IP packets permitted by the
access list can be translated
interface. You can include an access list to control which broadcasts
are forwarded. When an access list, only IP packets permitted by the
access list can be translated
Note
The ip directed-broadcast interface configuration command
can be configured on a VPN routing/forwarding(VRF)
interface and is VRF aware. Directed broadcast traffic is
routed only within the VRF.
can be configured on a VPN routing/forwarding(VRF)
interface and is VRF aware. Directed broadcast traffic is
routed only within the VRF.
Step 4
exit
Return to global configuration mode.
Step 5
ip forward-protocol {udp [port] | nd | sdns} Specify which protocols and ports the router forwards when
forwarding broadcast packets.
•
udp—Forward UPD datagrams.
port: (Optional) Destination port that controls which UDP
services are forwarded.
services are forwarded.
•
nd—Forward ND datagrams.
•
sdns—Forward SDNS datagrams
Step 6
end
Return to privileged EXEC mode.
Step 7
show ip interface [interface-id]
or
show running-config
Verify the configuration on the interface or all interfaces.
Step 8
copy running-config startup-config
(Optional) Save your entries in the configuration file.