RE: ip helper-address

From: Jonathan Hays (nomad@gfoyle.org)
Date: Sun Dec 14 2003 - 23:13:49 GMT-3


you wrote:
so that means the following pairs of command MUST be used together ?
thanks.

1) if default 8 ports are required
ip helper-address
ip forward-protocol udp

2) if additional udp port is required
ip helper-address
ip forward-protocol udp <new_port>

rgds,
alec

= = =

No.

The "ip forward-protocol" command is NOT necessary in case 1). I have
set up routers with only "ip helper-address" configured many, many
times. It works. I doubt you will take my word for it, so look at this
URL.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fipras_r/1rfipadr.htm#1018608

"The UDP destination port must be for TFTP, Domain Name System (DNS),
Time, NetBIOS, ND, BOOTP or DHCP packet, or a UDP port specified by the
ip forward-protocol udp global configuration command."

Carefully note the word "or" in the sentence above. If the desired
port(s) is in the "ip helper-address" list of ports then no "ip
forward-protocol" command need be configured.

Also, look at the example in the same URL:

"Examples

The following example defines an address that acts as a helper address:

interface ethernet 1
 ip helper-address 121.24.43.2"

The "ip forward-protocol" command is used only if you need to forward a
port that is not in the standard "helper-address" ports, or disable
forwarding for one or more of the default "helper-address" ports.

HTH,

Jonathan



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