What is the command syntax to tell a Cisco router to relay (forward?)
DHCP/BOOTP requests to another network (where the DHCP server actually
resides)?

Is it something similar to 'DHCP relay <ipaddress of server> or else
perhaps Cisco does not allow this type of broadcast?

Bob.
--
Bob Adams.
(amster has been killed by spam.)

email to: bob55@ntlworld.com

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You need to use an IP helper address. Below is the information for this
command from the Cisco site.

-Brian
--------------------------
ip helper-address
To have the Cisco IOS software forward User Datagram Protocol (UDP)
broadcasts, including BOOTP, received on an interface, use the ip
helper-address interface configuration command. To disable the forwarding of
broadcast packets to specific addresses, use the no form of this command.

ip helper-address address
no ip helper-address address
Syntax Description

address
Destination broadcast or host address to be used when forwarding UDP
broadcasts. There can be more than one helper address per interface.



Defaults

Disabled

Command Modes

Interface configuration

Command History

Release Modification
10.0
This command was introduced.



Usage Guidelines

Combined with the ip forward-protocol global configuration command, the ip
helper-address command allows you to control which broadcast packets and
which protocols are forwarded.

One common application that requires helper addresses is Dynamic Host
Configuration Protocol (DHCP), which is defined in rfc 1531. DHCP protocol
information is carried inside of BOOTP packets. To enable BOOTP broadcast
forwarding for a set of clients, configure a helper address on the router
interface closest to the client. The helper address should specify the
address of the DHCP server. If you have multiple servers, you can configure
one helper address for each server. Because BOOTP packets are forwarded by
default, DHCP information can now be forwarded by the router. The DHCP
server now receives broadcasts from the DHCP clients.

All of the following conditions must be met in order for a UDP or IP packet
to be helpered by the ip helper-address command:

a.. The MAC address of the received frame must be all-ones broadcast
address (ffff.ffff.ffff).
b.. The IP destination address must be one of the following: all-ones
broadcast (255.255.255.255), subnet broadcast for the receiving interface;
or major-net broadcast for the receiving interface if the no ip classless
command is also configured.
c.. The IP time-to-live (TTL) value must be at least 2.
d.. The IP protocol must be UDP (17).
e.. 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.
----------------------------------------------------------------------------
--
Note The ip helper-address command does not work on an X.25
interfaceon a destination router because the router cannot determine if the
packet was intended as a physical broadcast.

----------------------------------------------------------------------------
--

Examples

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

interface ethernet 1
ip helper-address 121.24.43.2
Related Commands

Command Description
ip forward-protocol
Specifies which protocols and ports the router forwards when forwarding
broadcast packets.



Related Commands

Command Description
ip forward-protocol
Specifies which protocols and ports the router forwards when forwarding
broadcast packets.






"Bob Adams" <nospam@ntlworld.com> wrote in message
news:4DMzoOGj6XJ$Ew79@ntlworld
.com...
> What is the command syntax to tell a Cisco router to relay (forward?)
> DHCP/BOOTP requests to another network (where the DHCP server actually
> resides)?
>
> Is it something similar to 'DHCP relay <ipaddress of server> or else
> perhaps Cisco does not allow this type of broadcast?
>
> Bob.
> --
> Bob Adams.
> (amster has been killed by spam.)
>
> email to: bob55@ntlworld.com


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In message <3f258550$1@news.sti.net>, Brian Lehigh <brianl@sti.net>
writes
>You need to use an IP helper address. Below is the information for this
>command from the Cisco site.
>
>-Brian
Thank you Brian. A brilliant answer.
Helper address huh? No wonder I couldn't find it! :-)

--
Bob Adams.
(amster has been killed by spam.)

email to: bob55@ntlworld.com

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