draft-sparks-sip-nit-problems-02.txt   rfc4321.txt 
Network Working Group R. Sparks Network Working Group R. Sparks
Internet-Draft Xten Request for Comments: 4321 Estacado Systems
Expires: July 2, 2005 Jan 2005 Category: Informational January 2006
Problems identified associated with the Session Initiation Protocol's
non-INVITE Transaction
draft-sparks-sip-nit-problems-02
Status of this Memo
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http://www.ietf.org/ietf/1id-abstracts.txt. Session Initiation Protocol's (SIP) Non-INVITE Transaction
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2006).
Abstract Abstract
This draft describes several problems that have been identified with This document describes several problems that have been identified
the Session Initiation Protocol's non-INVITE transaction. with the Session Initiation Protocol's (SIP) non-INVITE transaction.
Table of Contents Table of Contents
1. Problems under the current specifications . . . . . . . . . . 3 1. Problems under the Current Specifications .......................2
1.1 NITs must complete immediately or risk losing a race . . . 3 1.1. NITs must complete immediately or risk losing a race .......2
1.2 Provisional responses can delay recovery from lost 1.2. Provisional responses can delay recovery from lost
final responses . . . . . . . . . . . . . . . . . . . . . 4 final responses ............................................3
1.3 Delayed responses will temporarily blacklist an element . 5 1.3. Delayed responses will temporarily blacklist an element ....4
1.4 408 for non-INVITE is not useful . . . . . . . . . . . . . 7 1.4. 408 for non-INVITE is not useful ...........................6
1.5 Non-INVITE timeouts doom forking proxies . . . . . . . . . 8 1.5. Non-INVITE timeouts doom forking proxies ...................7
1.6 Mismatched timer values make winning the race harder . . . 8 1.6. Mismatched timer values make winning the race harder .......7
2. Security Considerations . . . . . . . . . . . . . . . . . . . 9 2. Security Considerations .........................................8
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 3. Acknowledgements ................................................8
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 4. Informative References ..........................................9
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 10
1. Problems under the current specifications 1. Problems under the Current Specifications
There are a number of unpleasant edge conditions created by the SIP There are a number of unpleasant edge conditions created by the SIP
non-INVITE transaction (NIT) model's fixed duration. The negative non-INVITE transaction (NIT) model's fixed duration. The negative
aspects of some of these are exacerbated by the effect provisional aspects of some of these are exacerbated by the effect that
responses have on the non-INVITE transaction state machines as provisional responses have on the non-INVITE transaction state
currently defined. machines as currently defined.
1.1 NITs must complete immediately or risk losing a race 1.1. NITs must complete immediately or risk losing a race
The non-INVITE transaction defined in RFC 3261 [1] is designed to The non-INVITE transaction defined in RFC 3261 [1] is designed to
have a fixed and finite duration (dependent on T1). A consequence of have a fixed and finite duration (dependent on T1). A consequence of
this design is that participants must strive to complete the this design is that participants must strive to complete the
transaction as quickly as possible. Consider the race condition transaction as quickly as possible. Consider the race condition
shown in Figure 1. shown in Figure 1.
UAC UAS UAC UAS
| request | | request |
--- |---. | --- |---. |
skipping to change at page 3, line 39 skipping to change at page 2, line 39
| | | | | | | |
| | | 64*T1 | | | 64*T1
| | | | | | | |
| | | | | | | |
v | | | v | | |
timeout <=== --- | 200 OK | | timeout <=== --- | 200 OK | |
| .---| v | .---| v
| .---' | --- | .---' | ---
|<--' | |<--' |
Figure 1: NI Race Condition Figure 1: Non-Invite Race Condition
The User Agent Server (UAS) in this figure believes it has responded The User Agent Server (UAS) in this figure believes it has responded
to the request in time, and that the request succeeded. The User to the request in time, and that the request succeeded. The User
Agent Client (UAC), on the other hand, believes the request has Agent Client (UAC), on the other hand, believes the request has
timed-out, hence failed. No longer having a matching client timed-out, hence failed. No longer having a matching client
transaction, the UAC core will ignore what it believes to be a transaction, the UAC core will ignore what it believes to be a
spurious response. As far as the UAC is concerned, it received no spurious response. As far as the UAC is concerned, it received no
response at all to its request. The ultimate result is the UAS and response at all to its request. The ultimate result is that the UAS
UAC have conflicting views of the outcome of the transaction. and UAC have conflicting views of the outcome of the transaction.
Therefore, a UAS cannot wait until the last possible moment to send a Therefore, a UAS cannot wait until the last possible moment to send a
final response within a NIT. It must, instead, send its response so final response within a NIT. It must, instead, send its response so
that it will arrive at the UAC before that UAC times out. that it will arrive at the UAC before that UAC times out.
Unfortunately, the UAS has no way to accurately measure the Unfortunately, the UAS has no way to accurately measure the
propagation time of the request or predict the propagation time of propagation time of the request or predict the propagation time of
the response. The uncertainty it faces is compounded by each proxy the response. The uncertainty it faces is compounded by each proxy
that participates in the transaction. Thus, the UAS's only choice is that participates in the transaction. Thus, the UAS's only choice is
to send its final response as soon as it possibly can and hope for to send its final response as soon as it possibly can and hope for
the best. the best.
skipping to change at page 4, line 32 skipping to change at page 3, line 32
direction. direction.
In specialized networks, a UAS might have some reliable knowledge of In specialized networks, a UAS might have some reliable knowledge of
inter-hop latency and could use that knowledge to determine if it has inter-hop latency and could use that knowledge to determine if it has
time to delay its final response in order to perform some processing time to delay its final response in order to perform some processing
such as a database lookup while mitigating its risk of losing the such as a database lookup while mitigating its risk of losing the
race in Figure 1. Establishing this knowledge across arbitrary race in Figure 1. Establishing this knowledge across arbitrary
networks (perhaps using resource reservation techniques and networks (perhaps using resource reservation techniques and
deterministic transports) is not currently feasible. deterministic transports) is not currently feasible.
1.2 Provisional responses can delay recovery from lost final responses 1.2. Provisional responses can delay recovery from lost final responses
The non-INVITE client transaction state machine provides reliability The non-INVITE client transaction state machine provides reliability
for NITs over unreliable transports (UDP) through retransmission of for NITs over unreliable transports (UDP) through retransmission of
the request message. Timer E is set to T1 when a request is the request message. Timer E is set to T1 when a request is
initially transmitted. As long as the machine remains in the Trying initially transmitted. As long as the machine remains in the Trying
state, each time Timer E fires, it will be reset to twice its state, each time Timer E fires, it will be reset to twice its
previous value (capping at T2) and the request is retransmitted. previous value (capping at T2) and the request is retransmitted.
If the non-INVITE client transaction state machine sees a provisional If the non-INVITE client transaction state machine sees a provisional
response, it transitions to the Proceeding state, where response, it transitions to the Proceeding state, where
retransmission continues, but the algorithm for resetting Timer E is retransmission continues, but the algorithm for resetting Timer E is
simply to use T2 instead of doubling at each firing. (Note that simply to use T2 instead of doubling at each firing. (Note that
Timer E is not altered during the transition to Proceeding). Timer E is not altered during the transition to Proceeding.)
Making the transition to the Proceeding state before Timer E is reset Making the transition to the Proceeding state before Timer E is reset
to T2 can cause recovery from a lost final response to take extra to T2 can cause recovery from a lost final response to take extra
time. Figure 2 shows recovery from a lost final response with and time. Figure 2 shows recovery from a lost final response with and
without a provisional message during this window. Recovery occurs without a provisional message during this window. Recovery occurs
within 2*T1 in the case without the provisional. With the within 2*T1 in the case without the provisional. With the
provisional, recovery is delayed until T2, which by default is 8*T1. provisional, recovery is delayed until T2, which by default is 8*T1.
In practical terms, a provisional response to a NIT in currently In practical terms, a provisional response to a NIT in currently
deployed networks can delay transaction completion by up to 3.5 deployed networks can delay transaction completion by up to 3.5
skipping to change at page 5, line 39 skipping to change at page 4, line 39
E = T2 E = T2
\/\ /\/ /\/ /\/ /\/ \/\ /\/ /\/ /\/ /\/
| | | | | | | | | |
| | v | | | | v | |
| | --- |----. | | | --- |----. |
| | | `--->| | | | `--->|
| | | .-----|(final) | | | .-----|(final)
| | |<--' | | | |<--' |
| | | | | | | |
Figure 2: Provisionals can harm recovery Figure 2: Provisionals Can Harm Recovery
No additional delay is introduced if the first provisional response No additional delay is introduced if the first provisional response
is received after Timer E has reached its maximum reset interval of is received after Timer E has reached its maximum reset interval of
T2. T2.
1.3 Delayed responses will temporarily blacklist an element 1.3. Delayed responses will temporarily blacklist an element
A SIP element's use of DNS SRV Resource Records [3] is specified in A SIP element's use of DNS Service Record Resource Records [3] is
RFC 3263 [2]. That specification discusses how SIP assures high specified in RFC 3263 [2]. That specification discusses how SIP
availability by having upstream elements detect failure of downstream ensures high availability by having upstream elements detect failure
elements. It proceeds to define several types of failure detection of downstream elements. It proceeds to define several types of
and instructions for failover. Two of the behaviors it describes are failure detection and instructions for failover. Two of the
important to this document: behaviors it describes are important to this document:
o Within a transaction, transport failure is detected either through o Within a transaction, transport failure is detected either through
an explicit report from the transport layer or through timeout. an explicit report from the transport layer or through timeout.
Note specifically that timeout will indicates transport failure Note specifically that timeout will indicates transport failure
regardless of the transport in use. When transport failure is regardless of the transport in use. When transport failure is
detected, the request is retried at the next element from the detected, the request is retried at the next element from the
sorted results of the SRV query. sorted results of the SRV query.
o Between transactions, locations reporting temporary failure o Between transactions, locations reporting temporary failure
(through 503/Retry-After for example) are not used until their (through 503/Retry-After, for example) are not used until their
requested black-out period expires. requested black-out period expires.
The specification notes the benefit of caching locations that are The specification notes the benefit of caching locations that are
successfully contacted, but does not discuss how such a cache is successfully contacted, but does not discuss how such a cache is
maintained. It is unclear whether an element should stop using maintained. It is unclear whether an element should stop using
(temporarily blacklist) a location returned in the SRV query that (temporarily blacklist) a location returned in the SRV query that
results in a transport error. If it does, when should such a results in a transport error. If it does, when should such a
location be removed from the blacklist? location be removed from the blacklist?
Without such a blacklist (or equivalent mechanism), the intended Without such a blacklist (or equivalent mechanism), the intended
availability mechanism fails miserably. Consider traffic between two availability mechanism fails miserably. Consider traffic between two
domains. Proxy pA in domain A needs to forward a sequence of domains. Proxy pA in domain A needs to forward a sequence of non-
non-INVITE requests to domain B. Through DNS SRV, pA discovers pB1 INVITE requests to domain B. Through DNS SRV, pA discovers pB1 and
and pB2, and the ordering rules of [2] and [3] indicate it should use pB2, and the ordering rules of [2] and [3] indicate it should use pB1
pB1 first. The first request to pB1 times out. Since pA is a proxy first. The first request to pB1 times out. Since pA is a proxy and
and a NIT has a fixed duration, pA has no opportunity to retry the a NIT has a fixed duration, pA has no opportunity to retry the
request at pB2. If pA does not remember pB1's failure, the second request at pB2. If pA does not remember pB1's failure, the second
request (and all subsequent non-INVITE requests until pB1 recovers) request (and all subsequent non-INVITE requests until pB1 recovers)
are doomed to the same failure. Caching would allow the subsequent are doomed to the same failure. Caching would allow the subsequent
requests to be tried at pB2. requests to be tried at pB2.
Since miserable failure is not acceptable in deployed networks, we Since miserable failure is not acceptable in deployed networks, we
should anticipate that elements will, in fact, cache timeout failures should anticipate that elements will, in fact, cache timeout failures
between transactions. Then the race in Figure 1 becomes important. between transactions. Then the race in Figure 1 becomes important.
If an element fails to respond "soon enough", it has effectively not If an element fails to respond "soon enough", it has effectively not
responded at all, and will be blacklisted at its peer for some period responded at all and will be blacklisted at its peer for some period
of time. of time.
(Note that even with caching, the first request timeout results in a (Note that even with caching, the first request timeout results in a
timeout failure all the way back to the original submitter. The timeout failure all the way back to the original submitter. The
failover mechanisms in [2] work well to increase the resiliency of a failover mechanisms in [2] work well to increase the resiliency of a
given INVITE transaction, but do nothing for a given non-INVITE given INVITE transaction, but do nothing for a given non-INVITE
transaction.) transaction.)
1.4 408 for non-INVITE is not useful 1.4. 408 for non-INVITE is not useful
Consider the race condition in Figure 1 when the final response is Consider the race condition in Figure 1 when the final response is
408 instead of 200. Under the current specification, the race is 408 instead of 200. Under the current specification, the race is
guaranteed to be lost. Most existing endpoints will emit a 408 for a guaranteed to be lost. Most existing endpoints will emit a 408 for a
non-INVITE request 64*T1 after receiving the request if they haven't non-INVITE request 64*T1 after receiving the request if they have not
emitted an earlier final response. Such a 408 is guaranteed to emitted an earlier final response. Such a 408 is guaranteed to
arrive at the next upstream element too late to be useful. In fact, arrive at the next upstream element too late to be useful. In fact,
in the presence of proxies, these messages are even harmful. When in the presence of proxies, these messages are even harmful. When
the 408 arrives, each proxy will have already terminated its the 408 arrives, each proxy will have already terminated its
associated client transaction due to timeout. So, each proxy must associated client transaction due to timeout. Therefore, each proxy
forward the 408 upstream statelessly. This, in turn, is guaranteed must forward the 408 upstream statelessly. This, in turn, is
to arrive too late. As Figure 3 shows, this can ultimately result guaranteed to arrive too late. As Figure 3 shows, this can
in bombarding the original requester with spurious 408s. (Note that ultimately result in bombarding the original requester with spurious
the proxy's client transaction state machine never enters the 408s. (Note that the proxy's client transaction state machine never
Completed state, so Timer K does not enter into play). enters the Completed state, so Timer K does not enter into play.)
UAC P1 P2 P3 UAS UAC P1 P2 P3 UAS
| | | | | | | | | |
--- ===---. | | | | --- ===---. | | | |
^ | `-->===---. | | | ^ | `-->===---. | | |
| | | `-->===---. | | | | | `-->===---. | |
| | | | `-->===---. | | | | | `-->===---. |
64*T1 | | | | `-->=== 64*T1 | | | | `-->===
| | | | | | | | | | | |
| | | | | | | | | | | |
skipping to change at page 7, line 43 skipping to change at page 6, line 43
| .-408=== | | | | .-408=== | | |
|<--' | .-408=== | | |<--' | .-408=== | |
| .-408-|<--' | .-408=== | | .-408-|<--' | .-408=== |
|<--' | .-408-|<--' | .-408=== |<--' | .-408-|<--' | .-408===
| .-408-|<--' | .-408-|<--' | | .-408-|<--' | .-408-|<--' |
|<--' | .-408-|<--' | | |<--' | .-408-|<--' | |
| .-408-|<--' | | | | .-408-|<--' | | |
|<--' | | | | |<--' | | | |
| | | | | | | | | |
Figure 3: late 408s to non-INVITEs Figure 3: Late 408s to Non-INVITEs
This response bombardment is not limited to the 408 response, though This response bombardment is not limited to the 408 response, though
it only exists when participating client transaction state machines it only exists when participating client transaction state machines
are timing out. Figure 4 generalizes Figure 1 to include multiple are timing out. Figure 4 generalizes Figure 1 to include multiple
hops. Note that even though the UAS responds "in time" to P3, the hops. Note that even though the UAS responds "in time" to P3, the
response is too late for P2, P1 and the UAC. response is too late for P2, P1, and the UAC.
UAC P1 P2 P3 UAS UAC P1 P2 P3 UAS
| | | | | | | | | |
--- ===---. | | | | --- ===---. | | | |
^ | `-->===---. | | | ^ | `-->===---. | | |
| | | `-->===---. | | | | | `-->===---. | |
| | | | `-->===---. | | | | | `-->===---. |
64*T1 | | | | `-->=== 64*T1 | | | | `-->===
| | | | | | | | | | | |
| | | | | | | | | | | |
v | | | | | v | | | | |
(timeout) --- === | | | | (timeout) --- === | | | |
| .-408=== | | .-200-| | .-408=== | | .-200-|
|<--' | .-408=== .-200-|<--' | |<--' | .-408=== .-200-|<--' |
| .-408-|<--'.-200-|<--' === | | .-408-|<--'.-200-|<--' === |
|<--'.-200-|<--' | | === |<--'.-200-|<--' | | ===
|<--' | | | | |<--' | | | |
| | | | | | | | | |
Figure 4: Additional timeout related error Figure 4: Additional Timeout-Related Error
1.5 Non-INVITE timeouts doom forking proxies 1.5. Non-INVITE timeouts doom forking proxies
A single branch with a delayed or missing final response will A single branch with a delayed or missing final response will
dominate the processing at proxy that receives no 2xx responses to a dominate the processing at proxy that receives no 2xx responses to a
forked non-INVITE request. Since this proxy is required to allow all forked non-INVITE request. This proxy is required to allow all of
of its client transactions to terminate before choosing a "best its client transactions to terminate before choosing a "best
response". This forces the proxy's server transaction to lose the response". This forces the proxy's server transaction to lose the
race in Figure 1. Any response it ultimately forwards (a 401 for race in Figure 1. Any response it ultimately forwards (a 401, for
example) will arrive at the upstream elements too late to be used. example) will arrive at the upstream elements too late to be used.
Thus, if no element among the branches would return a 2xx response, Thus, if no element among the branches would return a 2xx response,
failure of a single element (or its transport) dooms the proxy to failure of a single element (or its transport) dooms the proxy to
failure. failure.
1.6 Mismatched timer values make winning the race harder 1.6. Mismatched timer values make winning the race harder
There are many failure scenarios due to misconfiguration or There are many failure scenarios due to misconfiguration or
misbehavior that the SIP specification does not discuss. One is misbehavior that the SIP specification does not discuss. One is
placing two elements with different configured values for T1 and T2 placing two elements with different configured values for T1 and T2
on the same network. Review of Figure 1 illustrates that the race on the same network. Review of Figure 1 illustrates that the race
failure is only made more likely in this misconfigured state (it may failure is only made more likely in this misconfigured state (it may
appear that shortening T1 at the element behaving as a UAS improves appear that shortening T1 at the element behaving as a UAS improves
this particular situation, but remember that these elements may trade this particular situation, but remember that these elements may trade
roles on the next request). Since the protocol provides no mechanism roles on the next request). Since the protocol provides no mechanism
for discovering/negotiating a peer's timer values, exceptional care for discovering/negotiating a peer's timer values, exceptional care
must be taken when deploying systems with non-defaults to ensure they must be taken when deploying systems with non-defaults to ensure that
will _never_ directly communicate with elements with default values. they will never directly communicate with elements with default
values.
2. Security Considerations 2. Security Considerations
This document describes problems with the SIP non-INVITE transaction, This document describes some problems in the core SIP specification
including mentioning potential security vulnerabilities. It does not [1] related to the SIP non-INVITE requests, the messages other than
make any changes to the SIP protocol. INVITE that begin transactions. A few of the problems lead to
flooding or forgery risk, and could possibly be exploited by an
adversary in a denial of service attack. Solutions are defined in
the companion document [4].
3. IANA Considerations One solution there prohibits proxies and User Agents from sending 408
responses to non-INVITE transactions. Without this change, proxies
automatically generate a storm of useless responses. An attacker
could capitalize on this by enticing User Agents to send non-INVITE
requests to a black hole (through social engineering or DNS
poisoning) or by selectively dropping responses.
This document requires no action by IANA. Another solution prohibits proxies from forwarding late responses.
Without this change, an attacker could easily forge messages which
appear to be late responses. All proxies compliant with RFC 3261 are
required to forward these responses, wasting bandwidth and CPU and
potentially overwhelming target User Agents (especially those with
low speed connections).
4. Acknowledgments 3. Acknowledgements
This document captures many conversations about non-INVITE issues. This document captures many conversations about non-INVITE issues.
Significant contributers include Ben Campbell, Gonzalo Camarillo, Significant contributers include Ben Campbell, Gonzalo Camarillo,
Steve Donovan, Rohan Mahy, Dan Petrie, Adam Roach, Jonathan Steve Donovan, Rohan Mahy, Dan Petrie, Adam Roach, Jonathan
Rosenberg, and Dean Willis. Rosenberg, and Dean Willis.
5 References 4. Informative References
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[2] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol [2] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002. (SIP): Locating SIP Servers", RFC 3263, June 2002.
[3] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for [3] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
February 2000. February 2000.
[4] Sparks, R., "Actions Addressing Identified Issues with the
Session Initiation Protocol's (SIP) Non-INVITE Transaction", RFC
4320, January 2006.
Author's Address Author's Address
Robert J. Sparks Robert J. Sparks
Xten Estacado Systems
5100 Tennyson Parkway 17210 Campbell Road
Suite 1000 Suite 250
Plano, TX 75024 Dallas, TX 75252-4203
EMail: rsparks@xten.com EMail: rjsparks@estacado.net
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
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.
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.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights 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 might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 10, line 29 skipping to change at page 10, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Disclaimer of Validity Acknowledgement
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 Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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