draft-ietf-dhc-client-id-06.txt   draft-ietf-dhc-client-id-07.txt 
DHC Working Group N. Swamy DHC Working Group N. Swamy
Internet-Draft Samsung India Internet-Draft Samsung India
Updates: 2131 (if approved) G. Halwasia Updates: 2131 (if approved) G. Halwasia
Intended status: Standards Track P. Jhingran Intended status: Standards Track P. Jhingran
Expires: April 5, 2013 Cisco Systems Expires: May 9, 2013 Cisco Systems
October 2, 2012 November 5, 2012
Client Identifier Option in DHCP Server Replies Client Identifier Option in DHCP Server Replies
draft-ietf-dhc-client-id-06 draft-ietf-dhc-client-id-07
Abstract Abstract
This document updates RFC2131 [RFC2131]. The changes to [RFC2131] This document updates RFC 2131 -- Dynamic Host Configuration Protocol
defined in this draft clarifies the use of 'client identifier' option (DHCP) -- by addressing the issues arising from that document's
by the DHCP servers. The clarification addresses the issues arising specification that the server MUST NOT return the 'client identifier'
out of the point specified by [RFC2131] that the server 'MUST NOT' option to the client.
return client identifier' option to the client.
Requirements Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 5, 2013. This Internet-Draft will expire on May 9, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 4 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
3. Proposed Modification To [RFC2131] . . . . . . . . . . . . . . 5 3. Modification To [RFC2131] . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
The Dynamic Host Configuration Protocol (DHCP) defined in [RFC2131] The Dynamic Host Configuration Protocol (DHCP) defined in [RFC2131]
provides configuration parameters to hosts on a TCP/IP based network. provides configuration parameters to hosts on an IP based network.
DHCP is built on a client-server model, where designated DHCP server DHCP is built on a client-server model, where designated DHCP servers
allocate network addresses and deliver configuration parameters to allocate network addresses and deliver configuration parameters to
dynamically configured hosts. dynamically configured hosts.
The changes to [RFC2131] defined in this document clarifies the use The changes to [RFC2131] defined in this document clarify the use of
of 'client identifier' option by the DHCP servers. The clarification the 'client identifier' option by the DHCP servers. The
addresses the issues (as mentioned in Problem Statement) arising out clarification addresses the issues (as mentioned in Problem
of the point specified by [RFC2131] that the server 'MUST NOT' return Statement) arising out of the point specified by [RFC2131] that the
client identifier' option to the client. server 'MUST NOT' return 'client identifier' option to the client.
2. Problem Statement 2. Problem Statement
[RFC2131] specifies that a combination of 'client identifier' or [RFC2131] specifies that a combination of 'client identifier' or
'chaddr' and assigned network address constitute a unique identifier 'chaddr' and assigned network address constitute a unique identifier
for the client's lease and are used by both the client and server to 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 identify a lease referred in any DHCP messages. [RFC2131] also
specifies that the server "MUST NOT" return 'client identifier' in specifies that the server "MUST NOT" return 'client identifier' in
DHCPOFFER and DHCPACK messages. DHCP relay agents and servers, DHCPOFFER and DHCPACK messages. Furthermore, DHCP relay agents and
following these recommendations MAY drop the DHCP packets in the servers implementing [RFC2131] "MAY" drop the DHCP packets in the
absence of both 'client identifier' and 'chaddr'. absence of both 'client identifier' and 'chaddr'.
In some cases, client may not be having valid hardware address value In some cases, a client may not have a valid hardware address to
to be filled in 'chaddr' field of the packet and hence may set this populate the 'chaddr' field and may set the field to all zeroes. One
field as zero. One such example is when DHCP is used to assign IP such example is when DHCP is used to assign IP address to a mobile
address to a mobile phone or a tablet and where the 'chaddr' field is phone or a tablet and where the 'chaddr' field is set to zero in DHCP
set to zero in DHCP request packets. In such cases, client usually request packets. In such cases, client usually sets the 'client
sets the 'client identifier' option field (to a value as permitted in identifier' option field (to a value as permitted in [RFC2131]), and
[RFC2131]), and both client and server use this field to uniquely both client and server use this field to uniquely identify the client
identify the client with in a subnet. with in a subnet.
Note that due to above mentioned recommendations in [RFC2131], valid Note that due to above mentioned recommendations in [RFC2131], valid
downstream DHCP packets (DHCPOFFER, DHCPACK and DHCPNAK) from the downstream DHCP packets (DHCPOFFER, DHCPACK and DHCPNAK) from the
server MAY get dropped at the DHCP relay agent in the absence of server MAY get dropped at the DHCP relay agent in the absence of
'client identifier' option when 'chaddr' field is set as zero. 'client identifier' option when 'chaddr' field is set as zero.
The problem may get aggravated when a client receives a response from The problem may get aggravated when a client receives a response from
the server without 'client identifier' and with 'chaddr' value set to the server without 'client identifier' and with 'chaddr' value set to
zero, as it cannot guarantee that the response is intended for it. zero, as it cannot guarantee that the response is intended for it.
This is because even though the 'xid' field is present to map This is because even though the 'xid' field is present to map
responses with requests, this field alone cannot guarantee that a responses with requests, this field alone cannot guarantee that a
particular response is for a particular client, as 'xid' values particular response is for a particular client, as 'xid' values
generated by multiple clients within a subnet need not be unique. generated by multiple clients within a subnet need not be unique.
Lack of 'client identifier' option in DHCP reply messages also Lack of 'client identifier' option in DHCP reply messages also
affects the scenario where multiple DHCP clients may be running on affects the scenario where multiple DHCP clients may be running on
the same host sharing the same 'chaddr'. the same host sharing the same 'chaddr'.
This document attempts to address these problems faced by DHCP relay This document attempts to address these problems faced by DHCP relay
agent and client by proposing modification to DHCP server behavior. agent and client by proposing modification to DHCP server behavior.
The proposed solution is in line with DHCPv6 [RFC3315] where the The solution specified in this document is in line with DHCPv6
server always includes the Client Identifier option in the Reply [RFC3315] where the server always includes the Client Identifier
messages. option in the Reply messages.
3. Proposed Modification To [RFC2131] 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.
If the 'client identifier' option is set in a message received from a 3. Modification To [RFC2131]
client, the server MUST return the 'client identifier' option,
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. unaltered, in its response message.
Following table is extracted from section 4.3.1 of [RFC2131] and Following table is extracted from section 4.3.1 of [RFC2131] and
relevant fields are modified accordingly to overcome the problems relevant fields are modified accordingly to overcome the problems
mentioned in this document. mentioned in this document.
Option DHCPOFFER DHCPACK DHCPNAK Option DHCPOFFER DHCPACK DHCPNAK
------ --------- ------- ------- ------ --------- ------- -------
Client identifier (if MUST MUST MUST Client identifier (if MUST MUST MUST
sent by client) sent by client)
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identifier' option, the client MUST compare that client identifier to identifier' option, the client MUST compare that client identifier to
the one it is configured to send. If the two client identifiers do the one it is configured to send. If the two client identifiers do
not match, the client MUST silently discard the message. not match, the client MUST silently discard the message.
4. IANA Considerations 4. IANA Considerations
This memo asks the IANA for no new parameters. This memo asks the IANA for no new parameters.
5. Security Considerations 5. Security Considerations
No known 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. Acknowledgements 6. Acknowledgments
The authors would like to thank Bernie Volz, Ted Lemon, Barr Hibbs, The authors would like to thank Bernie Volz, Ted Lemon, Barr Hibbs,
Richard Johnson for their insightful discussions on the previous Richard Johnson, Barry Leiba, Stephen Farrell, Adrian Farrel for
version of this document. insightful discussions and review.
7. Normative References 7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", [RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997. RFC 2131, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
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