DHC Working Group S. Daniel Park
Internet-Draft Pyungsoo Kim
Expires : 27 May 2004 SAMSUNG Electronics
Bernie Volz
(unaffiliated)
28 November 2003
Rapid Commit Option for DHCPv4
draft-ietf-dhc-rapid-commit-opt-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document defines a new DHCPv4 option, modeled on the DHCPv6
Rapid Commit option, for obtaining IP address and configuration
information using a 2-message exchange rather than the usual 4-
message exchange, expediting client configuration.
Park, Kim, Volz [Expires: 27 May 2004] [Page 1]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
Table of Contents
1. Introduction.................................................2
2. Requirements.................................................3
3. Client/Server Operations.....................................3
3.1 Detailed Flow................................................3
3.2 Administrative Considerations................................7
4. Rapid Commit Option Format...................................8
5. IANA Considerations..........................................8
6. Security Considerations......................................8
7. References...................................................9
7.1 Normative References.........................................9
7.2 Informative References.......................................9
8. Author' Addresses............................................9
9. Acknowledgements............................................10
1. Introduction
In some environments, such as those in which high mobility occurs
and the network attachment point changes frequently, it is benefical
to rapidly configure clients. And, in these environments it is
possible to more quickly configure clients because the protections
offered by the normal (and longer) 4-message exchange may not be
needed. The 4-message exchange allows for redundancy (multiple DHCP
servers) without wasting addresses, as addresses are only
provisionally assigned to a client until the client chooses and
requests one of the provisionally assigned addresses. The 2-message
exchange may therefore be used when only one server is present or
when addresses are plentiful and having multiple servers commit
addresses for a client is not a problem.
This document defines a new Rapid Commit option for DHCPv4, modeled
on the DHCPv6 Rapid Commit option [RFC3315], which can be used to
initiate a 2-message exchange to expedite client configuration in
some environments. A client advertises its support of this option
by sending it in DHCPDISCOVER messages. A server then determines
whether to allow the 2-message exchange based on its configuration
information and can either handle the DHCPDISCOVER as defined in
[RFC2131] or commit the client's configuration information and
advance to sending a DHCPACK message with the Rapid Commit option
as defined herein.
Park, Kim, Volz [Expires: 27 May 2004] [Page 2]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
2. Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC 2119]
3. Client/Server Operations
A client that supports the Rapid Commit option SHOULD include it in
DHCPDISCOVER messages that it sends. The client MUST NOT include
it in any other messages.
A client that sent a DHCPDISCOVER with Rapid Commit option processes
responses as described in [RFC 2131]. However, if the client
receives a DHCPACK message with a Rapid Commit option, it SHOULD
process the DHCPACK immediately (without waiting for additional
DHCPOFFER or DHCPACK messages) and use the address and
configuration information contained therein.
A server that supports the Rapid Commit option MAY respond to a
DHCPDISCOVER message that included the Rapid Commit option with a
DHCPACK that includes the Rapid Commit option and fully committed
address and configuration information. A server MUST NOT include
the Rapid Commit option in any other messages.
The Rapid Commit option MUST NOT appear in a Parameter Request
List option [RFC 2132].
All other DHCP operations are as documented in [RFC 2131].
3.1 Detailed Flow
The following is a revised Section 3.1 of [RFC 2131] that includes
handling of the Rapid Commit option.
1. The client broadcasts a DHCPDISCOVER message on its local
physical subnet and SHOULD include the Rapid Commit option if
it supports this option. The DHCPDISCOVER message MAY include
Park, Kim, Volz [Expires: 27 May 2004] [Page 3]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
options that suggest values for the network address and lease
duration. BOOTP relay agents may pass the message on to DHCP
servers not on the same physical subnet.
2. Each server may respond with either a DHCPOFFER message or a
DHCPACK message with Rapid Commit option (the latter only if
the DHCPDISCOVER contained a Rapid Commit option and the
server's configuration policies allow use of Rapid Commit)
that includes an available network address in the 'yiaddr'
field (and other configuration parameters in DHCP options).
Servers sending a DHCPOFFER need not reserve the offered
network address, although the protocol will work more
efficiently if the server avoids allocating the offered
network address to another client. Servers sending the
DHCPACK message commit the binding for the client to
persistent storage before sending the DHCPACK. The
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 to in any DHCP messages. The
server transmits the DHCPOFFER or DHCPACK message to the
client, using the BOOTP relay agent if necessary.
When allocating a new address, servers SHOULD check that the
offered network address is not already in use; e.g., the
server may probe the offered address with an ICMP Echo Request.
Servers SHOULD be implemented so that network administrators
MAY choose to disable probes of newly allocated addresses.
Figure 3 in [RFC 2131] shows the flow for the normal 4-message
exchange. Figure 1 below shows the 2-message exchange.
Server Client Server
(not selected) (selected)
v v v
| | |
| Begins initialization |
| | |
| _____________/|\____________ |
|/DHCPDISCOVER | DHCPDISCOVER \|
| w/Rapid Commit| w/Rapid Commit|
| | |
Park, Kim, Volz [Expires: 27 May 2004] [Page 4]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
Determines | Determines
configuration | configuration
| | Commits configuration
| Collects replies |
|\ | ____________/|
| \________ | / DHCPACK |
| DHCPOFFER\ |/w/Rapid Commit|
| (discarded) | |
| Initialization complete |
| | |
. . .
. . .
| | |
| Graceful shutdown |
| | |
| |\ ____________ |
| | DHCPRELEASE \|
| | |
| | Discards lease
| | |
v v v
Figure 1: Timeline diagram when Rapid Commit used
3. The client receives one or more DHCPOFFER or DHCPACK (if Rapid
Commit option sent in DHCPDISCOVER) messages from one or more
servers. If a DHCPACK (with Rapid Commit option) is received,
the client may immediately advance to step 5 below if the
offered configuration parameters are acceptable. The client may
choose to wait for multiple responses. The client chooses one
server from which to request or accept configuration parameters,
based on the configuration parameters offered in the DHCPOFFER
and DHCPACK messages. If the client chooses a DHCPACK, it
advances to step 5. Otherwise, the client broadcasts a
DHCPREQUEST message that MUST include the 'server identifier'
option to indicate which server it has selected, and that MAY
include other options specifying desired configuration values.
The 'requested IP address' option MUST be set to the value of
'yiaddr' in the DHCPOFFER message from the server. This
DHCPREQUEST message is broadcast and relayed through DHCP/BOOTP
relay agents. To help ensure that any BOOTP relay agents
forward the DHCPREQUEST message to the same set of DHCP servers
Park, Kim, Volz [Expires: 27 May 2004] [Page 5]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
that received the original DHCPDISCOVER message, the
DHCPREQUEST message MUST use the same value in the DHCP message
header's 'secs' field and be sent to the same IP broadcast
address as the original DHCPDISCOVER message. The client times
out and retransmits the DHCPDISCOVER message if the client
receives no DHCPOFFER messages.
4. The servers receive the DHCPREQUEST broadcast from the client.
Those servers not selected by the DHCPREQUEST message use the
message as notification that the client has declined that
server's offer. The server selected in the DHCPREQUEST message
commits the binding for the client to persistent storage and
responds with a DHCPACK message containing the configuration
parameters for the requesting client. The 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
to in any DHCP messages. Any configuration parameters in the
DHCPACK message SHOULD NOT conflict with those in the earlier
DHCPOFFER message to which the client is responding. The
server SHOULD NOT check the offered network address at this
point. The 'yiaddr' field in the DHCPACK messages is filled in
with the selected network address.
If the selected server is unable to satisfy the DHCPREQUEST
message (e.g., the requested network address has been
allocated), the server SHOULD respond with a DHCPNAK message.
A server MAY choose to mark addresses offered to clients in
DHCPOFFER messages as unavailable. The server SHOULD mark an
address offered to a client in a DHCPOFFER message as available
if the server receives no DHCPREQUEST message from that client.
5. The client receives the DHCPACK message with configuration
parameters. The client SHOULD perform a final check on the
parameters (e.g., ARP for allocated network address), and notes
the duration of the lease specified in the DHCPACK message. At
this point, the client is configured. If the client detects
that the address is already in use (e.g., through the use of
ARP), the client MUST send a DHCPDECLINE message to the server
and restarts the configuration process. The client SHOULD wait
a minimum of ten seconds before restarting the configuration
process to avoid excessive network traffic in case of looping.
Park, Kim, Volz [Expires: 27 May 2004] [Page 6]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
If the client receives a DHCPNAK message, the client restarts
the configuration process.
The client times out and retransmits the DHCPREQUEST message if
the client receives neither a DHCPACK or a DHCPNAK message.
The client retransmits the DHCPREQUEST according to the
retransmission algorithm in section 4.1 of [RFC 2131]. The
client should choose to retransmit the DHCPREQUEST enough times
to give adequate probability of contacting the server without
causing the client (and the user of that client) to wait overly
long before giving up; e.g., a client retransmitting as
described in section 4.1 of [RFC 2131] might retransmit the
DHCPREQUEST message four times, for a total delay of 60 seconds,
before restarting the initialization procedure. If the client
receives neither a DHCPACK or a DHCPNAK message after employing
the retransmission algorithm, the client reverts to INIT
state and restarts the initialization process. The client
SHOULD notify the user that the initialization process has
failed and is restarting.
6. The client may choose to relinquish its lease on a network
address by sending a DHCPRELEASE message to the server. The
client identifies the lease to be released with its 'client
identifier', or 'chaddr' and network address in the DHCPRELEASE
message. If the client used a 'client identifier' when it
obtained the lease, it MUST use the same 'client identifier' in
the DHCPRELEASE message.
3.2 Administrative Considerations
Network administrators MUST only enable the use of Rapid Commit on a
DHCP server if one of the following conditions is met:
1. The server is the only server for the subnet.
2. Addresses are plentiful for the client population. When
multiple servers are present, they may each commit a binding
for all clients and therefore each server must have sufficient
addresses available.
Park, Kim, Volz [Expires: 27 May 2004] [Page 7]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
A server MAY allow configuration for a different (likely
shorter) initial lease time for addresses assigned when Rapid
Commit is used to expedite reclaiming addresses not used by
clients.
4. Rapid Commit Option Format
The Rapid Commit option is used to signal the use of the two message
exchange for address assignment. The code for the Rapid Commit
Option has to be defined (TBD). The format of the option is:
Code Len
+-----+-----+
| TBD | 0 |
+-----+-----+
A client SHOULD include this option in a DHCPDISCOVER message
if the client is prepared to perform the DHCPDISCOVER-DHCPACK
message exchange described earlier.
A server MUST include this option in a DHCPACK message sent in
a response to a DHCPDISCOVER message when completing the
DHCPDISCOVER-DHCPACK message exchange.
5. IANA Considerations
IANA is requested to assign a value for the Rapid Commit option code
in accordance with [RFC 2939].
6. Security Considerations
The concepts in this document do not significantly alter the
security considerations for DHCP (see [RFC 2131] and [RFC 3118]).
However, use of this option could expedite denial of service attacks
by allowing a mischievous client to more rapidly consume all
available addresses or to do so without requiring two-way
communication (as injecting DHCPDISCOVER messages with the Rapid
Park, Kim, Volz [Expires: 27 May 2004] [Page 8]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
Commit option is sufficient to cause a server to allocate an
address).
7. References
7.1 Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 2131] R. Droms, Dynamic Host Configuration Protocol, RFC 2131,
March 1997.
7.2 Informative References
[RFC 2132] Alexander, S. and Droms, R., "DHCP Options and BOOTP
Vendor Extensions," RFC 2132, March 1997.
[RFC 2939] R. Droms, Procedures and IANA Guidelines for Definition
of New DHCP Options and Message Types, RFC 2939,
September 2000.
[RFC 3118] R. Droms and W. Arbaugh, Authentication for DHCP
Messages, RFC 3118, June 2001.
[RFC 3315] R. Droms, et. al., Dynamic Host Configuration Protocol
for IPv6, RFC 3315, July 2003.
8. Author' Addresses
Soohong Daniel Park
Mobile Platform Laboratory, SAMSUNG Electronics
416, Maetan-3Dong, Paldal-Gu, Suwon
Gyeonggi-Do, Korea
Phone: +82-31-200-4508
EMail: soohong.park@samsung.com
Pyungsoo Kim
Park, Kim, Volz [Expires: 27 May 2004] [Page 9]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
Mobile Platform Laboratory, SAMSUNG Electronics
416, Maetan-3Dong, Paldal-Gu, Suwon
Gyeonggi-Do, Korea
Phone: +82-31-200-4635
Email: kimps@samsung.com
Bernie Volz
116 Hawkins Pond Road
Center Harbor, NH 03226-3103
USA
Phone: +1-603-968-3062
EMail: volz@metrocast.net
9. Acknowledgements
Special thanks to Ted Lemon and Andre Kostur for their many
valuable comments.
Notice Regarding Intellectual Property Rights
See http://www.ietf.org/ietf/IPR/samsung-general-patent04102003.txt
Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
Park, Kim, Volz [Expires: 27 May 2004] [Page 10]
Internet-Draft Rapid Commit Option for DHCPv4 28 November 2003
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Funding for the RFC editor function is currently provided by the
internet Society.
Park, Kim, Volz [Expires: 27 May 2004] [Page 11]
