Dell PowerEdge M420 Reference Manual page 906

(port 53), isakmp (port 500), mobile-ip (port 434), nameserver (port 42),
netbios-dgm (port 138), netbios-ns (port 137), ntp (port 123), pim-auto-
rp (port 496), rip (port 520), tacacs (port 49), tftp (port 69), and time
(port 37). Other ports must be specified by number.
Default Configuration
No helper addresses are configured.
Command Mode
Global Configuration mode.
User Guidelines
This command can be invoked multiple times, either to specify multiple
server addresses for a given port number or to specify multiple port numbers
handled by a specific server.
The command no ip helper-address with no arguments clears all global IP
helper addresses.
Example
To relay DHCP packets received on any interface to two DHCP servers,
10.1.1.1 and 10.1.2.1, use the following commands:
console#config
console(config)#ip helper-address 10.1.1.1 dhcp
console(config)#ip helper-address 10.1.2.1 dhcp
To relay UDP packets received on any interface for all default ports (see
Table 47-1) to the server at 20.1.1.1, use the following commands:
console#config
console(config)#ip helper-address 20.1.1.1
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IP Helper/DHCP Relay Commands