[Kea-users] Client-ID (option 61)

[Duane Wylie]

Many thanks to those who responded to help me with this.  Initially, I resolved this by modifying a user-supplied patch to remove this option from sent packets.


Today, I found the "proper" solution in the 1.2.0 documentation.  This is tested and working.


8.2.17. Echoing Client-ID (RFC 6842)

The original DHCPv4 specification (RFC 2131<http://tools.ietf.org/html/rfc2131>) states that the DHCPv4 server must not send back client-id options when responding to clients. However, in some cases that confused clients that did not have MAC address or client-id; see RFC 6842<http://tools.ietf.org/html/rfc6842>. for details. That behavior has changed with the publication of RFC 6842<http://tools.ietf.org/html/rfc6842> which updated RFC 2131<http://tools.ietf.org/html/rfc2131>. That update states that the server must send client-id if the client sent it. That is Kea's default behavior. However, in some cases older devices that do not support RFC 6842<http://tools.ietf.org/html/rfc6842>. may refuse to accept responses that include the client-id option. To enable backward compatibility, an optional configuration parameter has been introduced. To configure it, use the following configuration statement:

"Dhcp4": {
    "echo-client-id": false,
    ...
}




Duane Wylie



________________________________
From: Kea-users <kea-users-bounces at lists.isc.org> on behalf of Duane Wylie <duane.wylie at eatel.com>
Sent: Wednesday, August 9, 2017 3:57 PM
To: kea-users at lists.isc.org
Subject: [Kea-users] Client-ID (option 61)


We're evaluating KEA (version 1.2.0) as our DHCP platform moving forward.  In my testing with our Docsis/HFC network, I am not able to have a docsis modem respond to a DHCPOFFER message from KEA.  I can get the same modem to respond to a similarly formatted DHCPOFFER from ISC DHCP.


Looking at the tcpdump output from the server, the only difference that stands out is the Client-ID (option 61).  While, in both cases, the docsis modem does supply the Client-ID in the DHCPDISCOVER packet, the KEA server DOES include the Client-ID in the resulting DHCPOFFER where the ISC DHCP server DOES NOT include the Client-ID in it's DHCPOFFER.


(Interesting note: RFC 2131 (Draft Standard) states that the server "MUST NOT" include the Client-ID in the DHCPOFFER.  At the same time, RFC 6842 (Proposed Standard) indicates the server MUST include the Client-ID IF the client provided it in the DHCPDISCOVER.)


I need to determine why the KEA offer is not 'working'.  Admittedly, I do not know for certain that the Client-ID is the root of my problem.  I think the next step is to somehow prove that success or failure does indeed hinge on the inclusion of the Client-ID field in the DHCPOFFER.  I'm at somewhat of an impasse, as I cannot figure out how to tell KEA to NOT include the option.  (At the same time, I cannot figure out how to tell ISC DHCP to include the option - though this is off topic for the Kea-users list.)


Does anyone have any insight into a configuration option to disable option 61?  Is there a generic way to disable a certain option via the kea.conf file?  Or, where in the code can I 'flip the switch' the turn option 61 off on an offer?



Thanks in advance,

Duane

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