DHC Working Group N. Swamy
Internet-Draft Nokia
Updates: 2131 (if approved) G. Halwasia
Intended status: Standards Track P. Jhingran
Expires: January 12, 2013 Cisco Systems
July 11, 2012
Client Identifier Option in DHCP Server Replies
draft-ietf-dhc-client-id-04
Abstract
This document updates RFC2131 [RFC2131]. The changes to [RFC2131]
defined in this draft clarifies the use of 'client identifier' option
by the DHCP servers. The clarification addresses the issues arising
out of the point specified by [RFC2131] that the server 'MUST NOT'
return client identifier' option to the client.
Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 12, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
3. Proposed Modification To [RFC2131] . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Introduction
The Dynamic Host Configuration Protocol (DHCP) defined in [RFC2131]
provides configuration parameters to hosts on a TCP/IP based network.
DHCP is built on a client-server model, where designated DHCP server
allocate network addresses and deliver configuration parameters to
dynamically configured hosts.
The changes to [RFC2131] defined in this document clarifies the use
of 'client identifier' option by the DHCP servers. The clarification
addresses the issues (as mentioned in Problem Statement) arising out
of the point specified by [RFC2131] that the server 'MUST NOT' return
client identifier' option to the client.
2. Problem Statement
[RFC2131] specifies that a combination of 'client identifier' or
'chaddr' and assigned network address constitute a unique identifier
for the client's lease and are used by both the client and server to
identify a lease referred in any DHCP messages. [RFC2131] also
specifies that the server "MUST NOT" return 'client identifier' in
DHCPOFFER and DHCPACK messages. DHCP relay agents and servers,
following these recommendations MAY drop the DHCP packets in the
absence of both 'client identifier' and 'chaddr'.
In some cases, client may not be having valid hardware address value
to be filled in 'chaddr' field of the packet and hence may set this
field as zero. One such example is when DHCP is used to assign IP
address to a mobile phone or a tablet and where the 'chaddr' field is
set to zero in DHCP request packets. In such cases, client usually
sets the 'client identifier' option field (to a value as permitted in
[RFC2131]), and both client and server use this field to uniquely
identify the client with in a subnet.
Note that due to above mentioned recommendations in [RFC2131], valid
downstream DHCP packets (DHCPOFFER, DHCPACK and DHCPNAK) from the
server MAY get dropped at the DHCP relay agent in the absence of
'client identifier' option when 'chaddr' field is set as zero.
The problem may get aggravated when a client receives a response from
the server without 'client identifier' and with 'chaddr' value set to
zero, as it cannot guarantee that the response is intended for it.
This is because even though the 'xid' field is present to map
responses with requests, this field alone cannot guarantee that a
particular response is for a particular client, as 'xid' values
generated by multiple clients within a subnet need not be unique.
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Lack of 'client identifier' option in DHCP reply messages also
affects the scenario where multiple DHCP clients may be running on
the same host sharing the same 'chaddr'.
This document attempts to address these problems faced by DHCP relay
agent and client by proposing modification to DHCP server behavior.
The proposed solution is in line with DHCPv6 [RFC3315] where the
server always includes the Client Identifier option in the Reply
messages.
3. Proposed Modification To [RFC2131]
If the 'client identifier' option is set in a message received from a
client, the server MUST return the 'client identifier' option,
unaltered, in its response message.
Following table is extracted from section 4.3.1 of [RFC2131] and
relevant fields are modified accordingly to overcome the problems
mentioned in this document.
Option DHCPOFFER DHCPACK DHCPNAK
------ --------- ------- -------
Client identifier (if MUST MUST MUST
sent by client)
Client identifier (if MUST NOT MUST NOT MUST NOT
not sent by client)
When a client receives a DHCP message containing a 'client
identifier' option, the client MUST compare that client identifier to
the one it is configured to send. If the two client identifiers do
not match, the client MUST silently discard the message.
4. IANA Considerations
This memo asks the IANA for no new parameters.
5. Security Considerations
No known security considerations.
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6. Acknowledgements
The authors would like to thank Bernie Volz, Ted Lemon, Barr Hibbs,
Richard Johnson for their insightful discussions on the previous
version of this document.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
Authors' Addresses
Narasimha Swamy Nelakuditi
Nokia
Visiokatu 3
Tampere, 33720
Finland
Phone: +358 50487 2126
Email: narasimha.nelakuditi@nokia.com
Gaurav Halwasia
Cisco Systems
SEZ Unit, Cessna Business Park
Sarjapur Marathalli Outer Ring Road
Bangalore, 560103
India
Phone: +91 80 4426 1321
Email: ghalwasi@cisco.com
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Prashant Jhingran
Cisco Systems
SEZ Unit, Cessna Business Park
Sarjapur Marathalli Outer Ring Road
Bangalore, 560103
India
Phone: +91 80 4426 1800
Email: pjhingra@cisco.com
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