Cisco Cisco SG300-28 28-Port Gigabit Managed Switch Technical References

IP Addressing Commands

OL-32830-01 Command Line Interface Reference Guide

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Global Configuration mode

The command is supported only in router mode.

This command forwards specific UDP Broadcast packets from one interface to 
another, by specifying a UDP port number to which UDP broadcast packets with 
that destination port number are forwarded. By default, if no UDP port number is 
specified, the device forwards UDP broadcast packets for the following six 
services:

•

IEN-116 Name Service (port 42)

•

DNS (port 53)

•

NetBIOS Name Server (port 137)

•

NetBIOS Datagram Server (port 138)

•

TACACS Server (port 49)

•

Time Service (port 37)

Many helper addresses may be defined. However, the total number of 
address-port pairs is limited to 128 for the device.

The setting of a helper address for a specific interface has precedence over the 
setting of a helper address for all the interfaces.

Forwarding of BOOTP/DHCP (ports 67, 68) cannot be enabled with this command. 
Use the DHCP relay commands to relay BOOTP/DHCP packets.

The following example enables the forwarding of UDP Broadcast packets 
received on all interfaces to the UDP ports of a destination IP address and UDP 
port 1 and 2.

switchxxxxxx(config)# 

 172.16.9.9 49 53 1 2

Use the show ip helper-address Privileged EXEC mode command to display the IP 
helper addresses configuration on the system.