Forwarding Udp Broadcast Packets And Protocols - Cisco 3845 - Security Bundle Router Software Manual
Software configuration guide
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Chapter 29
Configuring IP Unicast Routing
Command
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]
or
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 that 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 find 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 configure 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 Command Reference, Volume 1 of 3: Addressing and Services, Release 12.2 lists the ports that
are forwarded by default if you do not specify any UDP ports.
If you do not specify any UDP ports when you configure the forwarding of UDP broadcasts, you are
configuring the router to act as a BOOTP forwarding agent. BOOTP packets carry DHCP information.
Beginning in privileged EXEC mode, follow these steps to enable forwarding UDP broadcast packets on
an interface and specify the destination address:
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
ip helper-address address
OL-23400-01
Purpose
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.
Purpose
Enter global configuration mode.
Enter interface configuration mode, and specify the Layer 3 interface
to configure.
Enable forwarding and specify the destination address for forwarding
UDP broadcast packets, including BOOTP.
Cisco ME 3800X and 3600X Switch Software Configuration Guide
Configuring IP Addressing
29-13
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