TCP Maintenance and Minor L. Eggert
Extensions (tcpm) NEC
Internet-Draft F. Gont
Expires: January 16, 2006 UTN/FRH
July 15, 2005
TCP User Timeout Option
draft-ietf-tcpm-tcp-uto-01
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
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.
This Internet-Draft will expire on January 16, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The TCP user timeout controls how long transmitted data may remain
unacknowledged before a connection is forcefully closed. It is a
local, per-connection parameter. The advisory TCP User Timeout
Option allows conforming TCP implementations to exchange their local
user timeouts. This exchange provides an in-protocol mechanism to
coordinate raising or lowering the two user timeouts of a connection.
Increase the user timeouts allows established TCP connections to
Eggert & Gont Expires January 16, 2006 [Page 1]
Internet-Draft TCP User Timeout Option July 2005
survive extended periods of disconnection. Decreasing user timeouts
allows busy servers to explicitly notify their clients that they will
maintain the connection state only across short periods of
disconnection.
1. Introduction
The Transmission Control Protocol (TCP) specification [RFC0793]
defines a local, per-connection "user timeout" parameter that
specifies the maximum amount of time that transmitted data may remain
unacknowledged before TCP will forcefully close the corresponding
connection. Applications can set and change this parameter with OPEN
and SEND calls. If a network disconnection lasts longer than the
user timeout, no acknowledgments will be received for any
transmission attempt, including keep-alives [TCP-ILLU], and the TCP
connection will close when the user timeout occurs. In the absence
of an application-specified user timeout, the TCP specification
[RFC0793] defines a default user timeout of 5 minutes.
The Host Requirements RFC [RFC1122] refines this definition by
introducing two thresholds, R1 and R2 (R2 > R1), on the number of
retransmissions of a single segment. It suggests that TCP notify
applications when R1 is reached for a segment, and close the
connection once R2 is reached. [RFC1122] also refines the
recommended values for R1 (three retransmissions) and R2 (100
seconds), noting that R2 for SYN segments should be at least 3
minutes. Instead of a single user timeout, some TCP implementations
offer finer-grained policies. For example, Solaris supports
different timeouts depending on whether a TCP connection is in the
SYN-SENT, SYN-RECEIVED, or ESTABLISHED state [SOLARIS-MANUAL].
Although applications may set their local user timeout, there is no
in-protocol mechanism to signal changes in the local user timeout to
remote peers. This causes local changes to be ineffective, because,
for example, the peer will still close the connection after its user
timeout expires, even when a host has raised its local user timeout.
The ability to modify the two user timeouts associated with a
connection in a coordinated manner can improve TCP operation in
scenarios that are currently not well supported. One example of such
scenarios are mobile hosts that change network attachment points
based on current location. Such hosts, maybe using MobileIP
[RFC3344], HIP [I-D.ietf-hip-arch] or transport-layer mobility
mechanisms [I-D.eddy-tcp-mobility], are only intermittently connected
to the Internet. In between connected periods, mobile hosts may
experience periods of disconnection during which no network service
is available [SCHUETZ-THESIS][SCHUETZ-CCR][DRIVE-THRU]. Other
factors that can cause transient periods of disconnection are high
levels of congestion as well as link or routing failures inside the
Eggert & Gont Expires January 16, 2006 [Page 2]
Internet-Draft TCP User Timeout Option July 2005
network.
In scenarios similar to the ones described above, a host may not know
exactly when or for how long it will be disconnected from the
network, but it might expect such events due to past mobility
patterns and thus benefit from using longer user timeouts. In other
scenarios, the length and time of a network disconnection may even be
predictable. For example, an orbiting node on a satellite might
experience disconnections due to line-of-sight blocking by other
planetary bodies. The disconnection periods of such a node may be
easily computable from orbital mechanics.
This document specifies a new TCP option - the User Timeout Option
(UTO) - that allows conforming hosts to exchange their local, per-
connection user timeout information. This allows, for example,
mobile hosts to maintain TCP connections across disconnected periods
that are longer than their peer's default user timeout. A second use
of the TCP User Timeout Option is advertisement of shorter-than-
default user timeouts. This can allow busy servers to explicitly
notify their clients that they will maintain the state associated
with established connections only across short periods of
disconnection.
The same benefits can be obtained through an application-layer
mechanism, i.e., coordinating changes to the user timeout values of a
connection through application messages. This approach does not
require a new TCP option, but requires application changes.
A different approach to tolerate longer periods of disconnection is
simply increasing the system-wide user timeout on both peers. This
approach has the benefit of not requiring a new TCP option. However,
it can also significantly increase the amount of connection state
information a busy server must maintain, because a longer global
timeout value will apply to all its connections. The proposed TCP
User Timeout Option, on the other hand, allows hosts to selectively
manage the user timeouts of individual connections, reducing the
amount of state they must maintain across disconnected periods.
2. Conventions
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].
3. Operation
Sending a TCP User Timeout Option suggests that the remote peer
SHOULD start using the indicated user timeout value for the
Eggert & Gont Expires January 16, 2006 [Page 3]
Internet-Draft TCP User Timeout Option July 2005
corresponding connection. The user timeout value included in a TCP
User Timeout Option specifies the requested user timeout during the
synchronized states of a connection (ESTABLISHED, FIN-WAIT-1, FIN-
WAIT-2, CLOSE-WAIT, CLOSING, or LAST-ACK). Connections in other
states MUST use standard timeout values [RFC0793][RFC1122]. [anchor4]
Note that an exchange of TCP User Timeout Options between peers is
not a binding negotiation. Transmission of a TCP User Timeout Option
is an advisory suggestion that the peer consider adapting its local
user timeout. Hosts remain free to forcefully close or abort
connections at any time for any reason, whether or not they use
custom user timeouts or have suggested to the peer to use them.
A host that supports the TCP User Timeout Option SHOULD include it in
the next possible segment to its peer whenever it starts using a new
user timeout for the connection. This allows the peer to adapt its
local user timeout for the connection accordingly.
When a host that supports the TCP User Timeout Option receives one,
it decides whether to change its local user timeout of the connection
based on the received value. Generally, hosts should honor requests
for changes to the user timeout (see Section 3.3), unless security
concerns, resource constraints or external policies indicate
otherwise (see Section 5). If so, hosts may ignore incoming TCP User
Timeout Options and use a different user timeout for the connection.
When a host receives a TCP User Timeout Option, it first decides
whether to change its local user timeout for the connection (see
Section 3.3) and then decides whether to send a TCP User Timeout
Option to its peer in response. If it has never sent a TCP User
Timeout Option to its peer during the lifetime of the connection or
if it has changed its local user timeout, it SHOULD send TCP User
Timeout Option with its current local user timeout to its peer.
[anchor5]
A host that supports the TCP User Timeout Option SHOULD include one
in each packet that carries a SYN flag, but need not. [MEDINA] has
shown that unknown options are correctly handled by the vast majority
of modern TCP stacks. It is thus not necessary to require
negotiation use of the TCP User Timeout Option for a connection.
A TCP implementation that does not support the TCP User Timeout
Option MUST silently ignore it [RFC1122], thus ensuring
interoperability.
Hosts SHOULD impose upper and lower limits on the user timeouts they
use. Section 3.3 discusses user timeout limits. A TCP User Timeout
Option with a value of zero (i.e., "now") is nonsensical and is used
Eggert & Gont Expires January 16, 2006 [Page 4]
Internet-Draft TCP User Timeout Option July 2005
for a special purpose, see Section 3.4. Section 3.3 discusses
potentially problematic effects of other user timeout durations.
3.1 Reliability Considerations
The TCP User Timeout Option is an advisory TCP option that does not
change processing for subsequent segments. Unlike other TCP options,
it need not be exchanged reliably. Consequently, the specification
in this section does not define a reliability handshake for TCP User
Timeout Option exchanges. When a segment that carries a TCP User
Timeout Option is lost, the option may never reach the intended peer.
Implementations MAY implement local mechanisms to improve delivery
reliability, such as retransmitting the TCP User Timeout Option when
they retransmit the segment that originally carried it or "attaching"
the option to a byte in the stream and retransmitting the option
whenever that byte or its ACK are retransmitted.
It is important to note that although these mechanisms can improve
transmission reliability for the TCP User Timeout Option, they do not
guarantee delivery (a three-way handshake would be required for
this). Consequently, implementations MUST NOT assume that a TCP User
Timeout Option is reliably transmitted.
3.2 Option Format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Kind = X | Length = 4 |G| User Timeout |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(One tick mark represents one bit.)
Figure 1: Format of the TCP User Timeout Option
Figure 1 shows the format of the TCP User Timeout Option. It
contains these fields:
Kind (8 bits)
A TCP option number [RFC0793] to be assigned by IANA upon
publication of this document (see Section 6).
Length (8 bits)
Length of the TCP option in octets [RFC0793]; its value MUST be 4.
Eggert & Gont Expires January 16, 2006 [Page 5]
Internet-Draft TCP User Timeout Option July 2005
Granularity (1 bit)
Granularity bit, indicating the granularity of the "User Timeout"
field. When set (G = 1), the time interval in the "User Timeout"
field MUST be interpreted as minutes. Otherwise (G = 0), the time
interval in the "User Timeout" field MUST be interpreted as
seconds.
User Timeout (15 bits)
Specifies the user timeout suggestion for this connection. It
MUST be interpreted as a 15-bit unsigned integer. The granularity
of the timeout (minutes or seconds) depends on the "G" field.
3.3 Duration of the User Timeout
The TCP User Timeout Option allows hosts to exchange user timeout
values from 1 second to over 9 hours at a granularity of seconds and
from 1 minute to over 22 days at a granularity of minutes. (An
option value of zero is reserved for a special purpose, see
Section 3.4.)
Very short user timeout values can affect TCP transmissions over
high-delay paths. If the user timeout occurs before an
acknowledgment for an outstanding segment arrives, possibly due to
packet loss, the connection closes. Many TCP implementations default
to user timeout values of a few minutes [TCP-ILLU]. Although the TCP
User Timeout Option allows suggestion of short timeouts, applications
advertising them SHOULD consider these effects.
Long user timeout values allow hosts to tolerate extended periods of
disconnection. However, they also require hosts to maintain the TCP
state information associated with connections for long periods of
time. Section 5 discusses the security implications of long timeout
values.
To protect against these effects, implementations SHOULD impose
limits on the user timeout values they accept and use. The remainder
of this section describes a RECOMMENDED scheme to limit user timeouts
based on upper and lower limits. Under the RECOMMENDED scheme, each
TCP SHOULD compute the user timeout (USER_TIMEOUT) for a connection
according to this formula:
USER_TIMEOUT = min(U_LIMIT, max(LOCAL_UTO, REMOTE_UTO, L_LIMIT))
Each field is to be interpreted as follows:
Eggert & Gont Expires January 16, 2006 [Page 6]
Internet-Draft TCP User Timeout Option July 2005
USER_TIMEOUT
Resulting user timeout value to be adopted by the local TCP for a
connection.
U_LIMIT
Current upper limit imposed on the user timeout of a connection by
the local host.
L_LIMIT
Current lower limit imposed on the user timeout of a connection by
the local host.
LOCAL_UTO
Current local user timeout of the specific connection.
REMOTE_UTO
Last "user timeout" value suggested by the remote peer by means of
the TCP User Timeout Option.
This means that the maximum of the two announced values will be
adopted for the user timeout of the connection. The rationale is
that choosing the maximum of the two values will let the connection
survive longer periods of disconnection. If the TCP that announced
the lower of the two user timeout values did so in order to reduce
the amount of TCP state information that must be kept on the host, it
can, nevertheless, close or abort the connection whenever it wants.
Enforcing a lower limit (L_LIMIT) prevents connections from closing
due to transient network conditions, including temporary congestion,
mobility hand-offs and routing instabilities.
An upper limit (U_LIMIT) can reduce the effect of resource exhaustion
attacks. Section 5 discusses the details of these attacks.
Note that these limits MAY be specified as system-wide constants or
at other granularities, such as on per-host, per-user or even per-
connection basis. Furthermore, these limits need not be static. For
example, they MAY be a function of system resource utilization or
attack status and could be dynamically adapted.
The Host Requirements RFC [RFC1122] does not impose any limits on the
length of the user timeout. However, a time interval of at least 100
seconds is RECOMMENDED. Consequently, the lower limit (L_LIMIT)
SHOULD be set to at least 100 seconds when following the RECOMMENDED
scheme described in this section.
Eggert & Gont Expires January 16, 2006 [Page 7]
Internet-Draft TCP User Timeout Option July 2005
3.4 Special Option Values
Whenever it is legal to do so according to the specification in the
previous sections, TCP implementations MAY send a zero-second TCP
User Timeout Option, i.e, with a "User Timeout" field of zero and a
"Granularity" of zero. This signals their peers that they support
the option, but do not suggest a specific user timeout value at that
time. Essentially, a zero-second TCP User Timeout Option acts as a
"don't care" value.
The receiver of a zero-second TCP User Timeout Option SHOULD perform
the RECOMMENDED strategy for calculating a new local USER_TIMEOUT
described in Section 3.3 with a numeric value of zero seconds for
REMOTE_UTO. The sender SHOULD perform the calculation as described
in Section 3.3. Essentially, the sender SHOULD adapt the peer's UTO
and the receiver SHOULD continue using its local UTO.
A zero-minute TCP User Timeout Option, i.e., with a "User Timeout"
field of zero and a "Granularity" bit of one, is reserved for future
use. TCP implementations MUST NOT sent it and MUST ignore it upon
reception.
4. Interoperability Issues
This section discusses interoperability issues related to introducing
the TCP User Timeout Option.
4.1 Middleboxes
The large number of middleboxes (firewalls, proxies, protocol
scrubbers, etc.) currently present in the Internet pose some
difficulty for deploying new TCP options. Some firewalls may block
segments that carry unknown options, preventing connection
establishment when the SYN or SYN-ACK contains a TCP User Timeout
Option. Some recent results, however, indicate that for new TCP
options, this may not be a significant threat, with only 0.2% of web
requests failing when carrying an unknown option [MEDINA].
Stateful firewalls usually reset connections after a period of
inactivity. If such a firewall exists along the path between two
peers, it may close or abort connections regardless of the use of the
TCP User Timeout Option. In the future, such firewalls may learn to
parse the TCP User Timeout Option and modify their behavior or the
option accordingly.
4.2 TCP Keep-Alives
Some TCP implementations, such as the one in BSD systems, use a
Eggert & Gont Expires January 16, 2006 [Page 8]
Internet-Draft TCP User Timeout Option July 2005
different abort policy for TCP keep-alives than for user data. Thus,
the TCP keep-alive mechanism might abort a connection that would
otherwise have survived the transient period of disconnection.
Therefore, if a TCP peer enables TCP keep-alives for a connection
that is using the TCP User Timeout Option, then the keep-alive timer
MUST be set to a value larger than that of the adopted USER TIMEOUT.
5. Security Considerations
Lengthening user timeouts has obvious security implications.
Flooding attacks cause denial of service by forcing servers to commit
resources for maintaining the state of throw-away connections. TCP
implementations do not become more vulnerable to simple SYN flooding
by implementing the TCP User Timeout Option, because user timeouts
negotiated during the handshake only affect the synchronized states
(ESTABLISHED, FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK),
which simple SYN floods never reach.
However, when an attacker completes the three-way handshakes of its
throw-away connections it can amplify the effects of resource
exhaustion attacks, because the attacked server must maintain the
connection state associated with the throw-away connections for
longer durations. Because connection state is kept longer, lower-
frequency attack traffic, which may be more difficult to detect, can
already cause resource exhaustion.
Several approaches can help mitigate this issue. First,
implementations can require prior peer authentication, e.g., using
IPsec [I-D.ietf-ipsec-rfc2401bis], before accepting long user
timeouts for the peer's connections. Similarly, a host can only
start to accept long user timeouts for an established connection
after in-band authentication has occurred, for example, after a TLS
handshake across the connection has succeeded [RFC2246]. Although
these are arguably the most complete solutions, they depend on
external mechanisms to establish a trust relationship.
A second alternative that does not depend on external mechanisms
would introduce a per-peer limit on the number of connections that
may use increased user timeouts. Several variants of this approach
are possible, such as fixed limits or shortening accepted user
timeouts with a rising number of connections. Although this
alternative does not eliminate resource exhaustion attacks from a
single peer, it can limit their effects. Reducing the number of
high-UTO connections a server supports in the face of an attack turns
that attack into a denial-of-service attack against the service of
high-UTO connections.
Per-peer limits cannot protect against distributed denial of service
Eggert & Gont Expires January 16, 2006 [Page 9]
Internet-Draft TCP User Timeout Option July 2005
attacks, where multiple clients coordinate a resource exhaustion
attack that uses long user timeouts. To protect against such
attacks, TCP implementations could reduce the duration of accepted
user timeouts with increasing resource utilization.
TCP implementations under attack may be forced to shed load by
resetting established connections. Some load-shedding heuristics,
such as resetting connections with long idle times first, can
negatively affect service for intermittently connected, trusted peers
that have suggested long user timeouts. On the other hand, resetting
connections to untrusted peers that use long user timeouts may be
effective. In general, using the peers' level of trust as a
parameter during the load-shedding decision process may be useful.
Note that if TCP needs to close or abort connections with a long TCP
User Timeout Option to shed load, these connections are still no
worse off than without the option.
Finally, upper and lower limits on user timeouts, discussed in
Section 3.3, can be an effective tool to limit the impact of these
sorts of attacks.
6. IANA Considerations
This section is to be interpreted according to [RFC2434].
This document does not define any new namespaces. It uses an 8-bit
TCP option number maintained by IANA at
http://www.iana.org/assignments/tcp-parameters.
7. Acknowledgments
The following people have improved this document through thoughtful
suggestions: Mark Allmann, David Borman, Marcus Brunner, Wesley Eddy,
Ted Faber, Guillermo Gont, Tom Henderson, Joseph Ishac, Jeremy
Harris, Phil Karn, Michael Kerrisk, Dan Krejsa, Kostas Pentikousis,
Juergen Quittek, Joe Touch, Stefan Schmid, Simon Schuetz and Martin
Stiemerling.
Lars Eggert is partly funded by Ambient Networks, a research project
supported by the European Commission under its Sixth Framework
Program. The views and conclusions contained herein are those of the
authors and should not be interpreted as necessarily representing the
official policies or endorsements, either expressed or implied, of
the Ambient Networks project or the European Commission.
8. References
Eggert & Gont Expires January 16, 2006 [Page 10]
Internet-Draft TCP User Timeout Option July 2005
8.1 Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
8.2 Informative References
[DRIVE-THRU]
Ott, J. and D. Kutscher, "Drive-Thru Internet: IEEE
802.11b for Automobile Users", Proc. Infocom , March 2004.
[I-D.eddy-tcp-mobility]
Eddy, W., "Mobility Support For TCP",
draft-eddy-tcp-mobility-00 (work in progress), April 2004.
[I-D.ietf-hip-arch]
Moskowitz, R., "Host Identity Protocol Architecture",
draft-ietf-hip-arch-02 (work in progress), January 2005.
[I-D.ietf-ipsec-rfc2401bis]
Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", draft-ietf-ipsec-rfc2401bis-06 (work
in progress), April 2005.
[MEDINA] Medina, A., Allman, M., and S. Floyd, "Measuring
Interactions Between Transport Protocols and Middleboxes",
Proc. 4th ACM SIGCOMM/USENIX Conference on Internet
Measurement , October 2004.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[SCHUETZ-CCR]
Schuetz, S., Eggert, L., Schmid, S., and M. Brunner,
"Protocol Enhancements for Intermittently Connected
Eggert & Gont Expires January 16, 2006 [Page 11]
Internet-Draft TCP User Timeout Option July 2005
Hosts", To appear: ACM Computer Communication Review, Vol.
35, No. 3, July 2005.
[SCHUETZ-THESIS]
Schuetz, S., "Network Support for Intermittently Connected
Mobile Nodes", Diploma Thesis, University of Mannheim,
Germany, June 2004.
[SOLARIS-MANUAL]
Sun Microsystems, "Solaris Tunable Parameters Reference
Manual", Part No. 806-7009-10, 2002.
[TCP-ILLU]
Stevens, W., "TCP/IP Illustrated, Volume 1: The
Protocols", Addison-Wesley , 1994.
Editorial Comments
[anchor4] LE: A future version of this document may extend per-
connection user timeouts to the SYN-SENT and SYN-RECEIVED
states in a way that conforms to the required minimum
timeouts.
[anchor5] LE: Should it really always send UTO when it changes the
local timeout? I can imagine some ping-pong effect when
two hosts user different UTO adoption strategies. But
maybe that's OK?
Authors' Addresses
Lars Eggert
NEC Network Laboratories
Kurfuerstenanlage 36
Heidelberg 69115
Germany
Phone: +49 6221 90511 43
Fax: +49 6221 90511 55
Email: lars.eggert@netlab.nec.de
URI: http://www.netlab.nec.de/
Eggert & Gont Expires January 16, 2006 [Page 12]
Internet-Draft TCP User Timeout Option July 2005
Fernando Gont
Universidad Tecnologica Nacional
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
Email: fernando@gont.com.ar
URI: http://www.gont.com.ar/
Appendix A. Document Revision History
To be removed upon publication
+-----------+-------------------------------------------------------+
| Revision | Comments |
+-----------+-------------------------------------------------------+
| 00 | Resubmission of |
| | draft-eggert-gont-tcpm-tcp-uto-option-01.txt to the |
| | secretariat after WG adoption. Thus, permit |
| | derivative works. Updated Lars Eggert's funding |
| | attribution. Updated several references. No technical |
| | changes. |
| 01 | Clarified and corrected the description of the |
| | existing user timeout in RFC793 and RFC1122. Removed |
| | distinction between operating during the 3WHS and the |
| | established states and introduced zero-second "don't |
| | care" UTOs in response to mailing list feedback. |
| | Updated references and addressed many other comments |
| | from the mailing list. |
+-----------+-------------------------------------------------------+
Eggert & Gont Expires January 16, 2006 [Page 13]
Internet-Draft TCP User Timeout Option July 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM 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.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Eggert & Gont Expires January 16, 2006 [Page 14]
