Internet DRAFT - draft-ietf-dhc-client-id
draft-ietf-dhc-client-id
DHC Working Group N. Swamy
Internet-Draft Samsung India
Updates: 2131 (if approved) G. Halwasia
Intended status: Standards Track P. Jhingran
Expires: May 9, 2013 Cisco Systems
November 5, 2012
Client Identifier Option in DHCP Server Replies
draft-ietf-dhc-client-id-07
Abstract
This document updates RFC 2131 -- Dynamic Host Configuration Protocol
(DHCP) -- by addressing the issues arising from that document's
specification that the server MUST NOT return the '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 May 9, 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
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
3. Modification To [RFC2131] . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 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 an IP based network.
DHCP is built on a client-server model, where designated DHCP servers
allocate network addresses and deliver configuration parameters to
dynamically configured hosts.
The changes to [RFC2131] defined in this document clarify the use of
the '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. Furthermore, DHCP relay agents and
servers implementing [RFC2131] "MAY" drop the DHCP packets in the
absence of both 'client identifier' and 'chaddr'.
In some cases, a client may not have a valid hardware address to
populate the 'chaddr' field and may set the field to all zeroes. 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 solution specified in this document is in line with DHCPv6
[RFC3315] where the server always includes the Client Identifier
option in the Reply messages.
The requirement for DHCP servers not to return the 'client
identifier' option was made purely to conserve the limited space in
the packet. It is possible, though unlikely, that clients will drop
packets that contain this formerly unexpected option. There are no
known client implementations that will drop packets but the benefit
provided by this change outweighs any small risk of such behavior.
More harm is being done by not having the 'client identifier' option
present than might be done by adding it now.
3. Modification To [RFC2131]
If the 'client identifier' option is present 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.
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5. Security Considerations
This specification does not add any new security considerations other
than the ones already mentioned in [RFC2131]. It is worth noting
that DHCP clients routinely connect to different IP networks managed
by different network providers. DHCP clients have no a priori
knowledge of which network they are connecting to. Consequently, the
client identifier will, by definition, be routinely shared with
network operators and could be used in ways that violate the user's
privacy. This is a problem that existed in [RFC2131]. This document
does nothing to address this problem.
6. Acknowledgments
The authors would like to thank Bernie Volz, Ted Lemon, Barr Hibbs,
Richard Johnson, Barry Leiba, Stephen Farrell, Adrian Farrel for
insightful discussions and review.
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
Samsung India
Block-B, Bagmane Lakeview,
66/1, Bagmane Tech Park,
Byrasandra, C.V. Raman Nagar, Bangalore, 560093
India
Phone: +91 80 4181 9999
Email: nn.swamy@samsung.com
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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
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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