812
Configuring IP Unicast Routing
Configuring IP Addressing
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.
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.
BEFORE YOU BEGIN
See the description for the
ip forward-protocol
interface configuration command in the
for the list of ports that are forwarded by default if you do not specify any UDP ports.
DETAILED STEPS
Use the
no ip helper-address
interface configuration command to disable the forwarding of broadcast packets to
specific addresses. Use the
no ip forward-protocol
global configuration command to remove a protocol or port.
EXAMPLE
The following example defines a helper address and uses the
ip forward-protocol
command. Using the
udp
keyword
without specifying any port numbers will allow forwarding of UDP packets on the default ports.
Switch#
configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#
interface ethernet 0
Switch(config-if)#
ip helper-address 10.24.42.2
Switch(config-if)#
exit
Command
Purpose
1.
configure terminal
Enter global configuration mode.
2.
interface
interface-id
Enter interface configuration mode, and specify the Layer 3
interface to configure.
3.
no shutdown
Enable the interface if necessary. By default, UNIs and ENIs
are disabled and NNIs are enabled.
4.
ip helper-address
address
Enable forwarding and specify the destination address for
forwarding UDP broadcast packets, including BOOTP.
5.
exit
Return to global configuration mode.
6.
ip forward-protocol
{
udp
[
port
]
| nd |
sdns
}
Specify which protocols the router forwards when
forwarding broadcast packets.
7.
end
Return to privileged EXEC mode.
8.
show ip interface
[
interface-id
]
or
show running-config
Verify the configuration on the interface or all interfaces.
9.
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Summary of Contents for IE 4000
Page 12: ...8 Configuration Overview Default Settings After Initial Switch Configuration ...
Page 52: ...48 Configuring Interfaces Monitoring and Maintaining the Interfaces ...
Page 108: ...104 Configuring Switch Clusters Additional References ...
Page 128: ...124 Performing Switch Administration Additional References ...
Page 130: ...126 Configuring PTP ...
Page 140: ...136 Configuring CIP Additional References ...
Page 146: ...142 Configuring SDM Templates Configuration Examples for Configuring SDM Templates ...
Page 192: ...188 Configuring Switch Based Authentication Additional References ...
Page 244: ...240 Configuring IEEE 802 1x Port Based Authentication Additional References ...
Page 298: ...294 Configuring VLANs Additional References ...
Page 336: ...332 Configuring STP Additional References ...
Page 408: ...404 Configuring DHCP Additional References ...
Page 450: ...446 Configuring IGMP Snooping and MVR Additional References ...
Page 490: ...486 Configuring SPAN and RSPAN Additional References ...
Page 502: ...498 Configuring Layer 2 NAT ...
Page 770: ...766 Configuring IPv6 MLD Snooping Related Documents ...
Page 930: ...926 Configuring IP Unicast Routing Related Documents ...
Page 976: ...972 Configuring Cisco IOS IP SLAs Operations Additional References ...
Page 978: ...974 Dying Gasp ...
Page 990: ...986 Configuring Enhanced Object Tracking Monitoring Enhanced Object Tracking ...
Page 994: ...990 Configuring MODBUS TCP Displaying MODBUS TCP Information ...
Page 996: ...992 Ethernet CFM ...
Page 1066: ...1062 Using an SD Card SD Card Alarms ...