How to configure dhclient to send option#82

[David Ganor]

Hi Niall,
Well, without going into too many details...
1. The system is a control host for a DPoE (DOCSIS Provisioning over EPON)
network:
	a. the DPoE-system is a Linux machine connected to an EPON manager
box, called an OLT.
	b. The OLT manages/controls an EPON optical network, in which each
node is terminated by a remote "MODEM", called an ONU.
	c. The ONU services network devices, such as computers, VOIP phones,
set-top boxes etc. These devices run an IP stack and needs to get an IP
address from a DHCP server.
	d. An ONU doesn't run an IP stack, but is managed via SNMP, through
an agent running on the system.
2. The system runs DHCP clients to get IP addresses for managed entities
(ONUs) and also acts as a DHCP relay, on behalf of non-managed, remote
devices.
3. Whenever a managed entity is connected and the associated SNMP agent
requests an IP address, it should also add option#82-suboption#9 with
enterprise number 4491 (indicating CabelLabs Inc., the owner of the DPoE and
DOCSIS specs)
4. The dhcrelay, as a standalone process, can probably be used for the phase
of getting the IP address, but doing the actual relaying job between 2
interfaces, on separated IP subnets is not feasible:
the DHCP messages from, and to, the non-managed remote devices don't go
through a "regular" (Linux) Ethernet interface - it's a special host-control
interface with a special control application (which we develop...)

I hope this not-so-short-after-all background overview makes my question a
little clearer, so to summarize:
Can I, somehow, run/connect/configure something(s) so that the DHCPDiscover
and DHCPRequest will include this option#82?

I know I can hard-code this option in the dhclient and re-build the
executable, but I would prefer not to...


Thak you for yout time,
David Ganor


-----Original Message-----
From: dhcp-users-bounces+david=oliver-solutions.com at lists.isc.org
[mailto:dhcp-users-bounces+david=oliver-solutions.com at lists.isc.org] On
Behalf Of Niall O'Reilly
Sent: Thursday, February 02, 2012 11:58 AM
To: Users of ISC DHCP
Subject: Re: How to configure dhclient to send option#82


On 2 Feb 2012, at 07:51, David Ganor wrote:

> I need to configure a dhclient to send option#82 with a specific
sub-option #9 in the DHCPDiscover and in the DHCPRequest messages.

	I believe that that's a need which is architecturally beyond what
DHCP
	is intended for.

	Option 82 is intended to be used for adding information to the DHCP
	exchange which is available on the relay device (usually a router),
	but not on the client.  By design, a client simply doesn't do option
82.

	From what you say, it appears to me that you need to communicate
some
	property of the client to the server, and that this property is
known 
	(by configuration) at the client.  I think you should best choose an
	appropriate option from among those that the client con be
configured
	to send.

	Without further information about what you are actually trying to
	achieve, and perhaps also about your network topology, it will be
	difficult for anyone on the list to give you advice relevant to
	your circumstances.


	Best regards,
	Niall O'Reilly

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