Forwarding Udp Broadcast Packets And Protocols - Cisco Catalyst 3550 series Software Configuration Manual

Configuring IP Addressing on Layer 3 Interfaces
Beginning in privileged EXEC mode, follow these steps to enable forwarding of IP-directed broadcasts
on an interface:
Command
Step 1 configure terminal
Step 2
interface interface-id
Step 3
ip directed-broadcast [access-list-number]
Step 4
exit
Step 5
ip forward-protocol {udp [port] | nd | sdns} Specify which protocols and ports the router forwards when
Step 6 end
Step 7
show ip interface [interface-id]
show running-config
Step 8
copy running-config startup-config
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.

Forwarding UDP Broadcast Packets and Protocols

User Datagram Protocol (UDP) is an IP host-to-host layer protocol, as is TCP. UDP provides a
low-overhead, connectionless session between two end systems and does not provide for
acknowledgment of received datagrams. Network hosts occasionally use UDP broadcasts to determine
address, configuration, and name information. If such a host is on a network segment that does not
include a server, UDP broadcasts are normally not forwarded. You can remedy this situation by
configuring an interface on a router to forward certain classes of broadcasts to a helper address. You can
use more than one helper address per interface.
You can specify a UDP destination port to control which UDP services are forwarded. You can specify
multiple UDP protocols. You can also specify the Network Disk (ND) protocol, which is used by older
diskless Sun workstations and the network security protocol SDNS.
By default, both UDP and ND forwarding are enabled if a helper address has been defined for an
interface. The description for the ip forward-protocol interface configuration command in the Cisco
IOS IP and IP Routing Command Reference for Release 12.1 lists the ports that are forwarded by default
if you do not specify any UDP ports.
Catalyst 3550 Multilayer Switch Software Configuration Guide
31-14
Purpose
Enter global configuration mode.
Enter interface configuration mode, and specify the interface to
configure.
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 is specified, only IP packets
permitted by the access list are eligible to be translated.
Return to global configuration mode.
forwarding broadcast packets.
• udp—Forward UPD datagrams.
port: (Optional) Destination port that controls which UDP
services are forwarded.
nd—Forward ND datagrams.
•
sdns—Forward SDNS datagrams
•
Return to privileged EXEC mode.
Verify the configuration on the interface or all interfaces.
(Optional) Save your entries in the configuration file.
Chapter 31 Configuring IP Unicast Routing
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