[Text version]

Network Working Group Request for Comments: 4222 BCP: 112 Category: Best Current Practice

G. Choudhury, Ed. AT&T October 2005

Status of This Memo

This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited.

Copyright Notice

Copyright © The Internet Society (2005).

Abstract

This document recommends methods that are intended to improve the scalability and stability of large networks using Open Shortest Path First (OSPF) Version 2 protocol. The methods include processing OSPF Hellos and Link State Advertisement (LSA) Acknowledgments at a higher priority compared to other OSPF packets, and other congestion avoidance procedures.

Table of Contents

   1. Introduction...................................................2
   2. Recommendations................................................3
   3. Security Considerations........................................6
   4. Acknowledgments................................................6
   5. Normative References...........................................6
   6. Informative References.........................................7
   Appendix A. LSA Storm: Causes and Impact..........................8
   Appendix B. List of Variables and Values.........................10
   Appendix C. Other Recommendations and Suggestions................11

1. Introduction

In this document, OSPF refers to OSPFv2 [Ref1]. The scalability and stability improvement techniques described here may also apply to OSPFv3 [Ref2], but that will require further study and operational experience.

A large network running OSPF protocol may occasionally experience the simultaneous or near-simultaneous update of a large number of link state advertisements, or LSAs. This is particularly true if OSPF traffic engineering extension [Ref3] is used that may significantly increase the number of LSAs in the network. We call this event an LSA storm and it may be initiated by an unscheduled failure or a scheduled maintenance event. The failure may be hardware, software, or procedural in nature.

The LSA storm causes high CPU and memory utilization at the router causing incoming packets to be delayed or dropped. Delayed acknowledgments (beyond the retransmission timer value) result in retransmissions, and delayed Hello packets (beyond the router-dead interval) result in neighbor adjacencies being declared down. The retransmissions and additional LSA originations result in further CPU and memory usage, essentially causing a positive feedback loop, which, in the extreme case, may drive the network to an unstable state.

The default value of the retransmission timer is 5 seconds and that of the router-dead interval is 40 seconds. However, recently there has been a lot of interest in significantly reducing OSPF convergence time. As part of that plan, much shorter (sub-second) Hello and router-dead intervals have been proposed [Ref4]. In such a scenario, it will be more likely for Hello packets to be delayed beyond the router-dead interval during network congestion caused by an LSA storm.

In order to improve the scalability and stability of networks, we recommend steps for prioritizing critical OSPF packets and avoiding congestion. The details of the recommendations are given in Section 2. A simulation study is reported in [Ref13] that quantifies the congestion phenomenon and its impact. It also studies several of the recommendations and shows that they indeed improve the scalability and stability of networks using OSPF protocol. [Ref13] is available on request by contacting the editor or one of the authors. Appendix A explains in more detail LSA storm scenarios, their impact, and points out a few real-life examples of control-message storms. Appendix B provides a list of variables used in the recommendations and their example values. Appendix C provides some further recommendations and suggestions with similar goals.

2. Recommendations

The recommendations below are intended to improve the scalability and stability of large networks using OSPF protocol. During periods of network congestion, they would reduce retransmissions, avoid an adjacency to be declared down due to Hello packets being delayed beyond the RouterDeadInterval, and take other congestion avoidance steps. The recommendations are unordered except that Recommendation 2 is to be implemented only if Recommendation 1 is not implemented.

   (1) Classify all OSPF packets in two classes: a "high priority" class
       comprising OSPF Hello packets and Link State Acknowledgement
       packets, and a "low priority" class comprising all other packets.
       The classification is accomplished by examining the OSPF packet
       header.  While receiving a packet from a neighbor and while
       transmitting a packet to a neighbor, try to process a "high
       priority" packet ahead of a "low priority" packet.

       The prioritized processing while transmitting may cause OSPF
       packets from a neighbor to be received out of sequence.  If
       Cryptographic Authentication (AuType = 2) is used (as specified
       in [Ref1]), then successive received valid OSPF packets from a
       neighbor need to have a non-decreasing "Cryptographic sequence
       number".  To comply with this requirement, we recommend that in
       case Cryptographic Authentication (AuType = 2) is used [Ref1],
       prioritized processing not be done at the transmitter.  This will
       avoid packets arriving at the receiver out of sequence.  However,
       after security processing at the receiver (including sequence
       number checking) is complete, the OSPF packets may be kept in a
       "high priority" queue or a "low priority" queue based on their
       class and processed accordingly.  The benefit of prioritized
       processing is clearly higher in the absence of Cryptographic
       Authentication since in that case prioritization can be
       implemented both at the transmitter and at the receiver.
       However, even with Cryptographic Authentication it will be
       beneficial to have prioritization only at the receiver (following
       security processing).

   (2) If Recommendation 1 cannot be implemented, then reset the
       inactivity timer for an adjacency whenever any OSPF unicast
       packet or any OSPF packet sent to AllSPFRouters over a point-to-
       point link is received over that adjacency instead of resetting

       the inactivity timer only on receipt of the Hello packet.  So
       OSPF would declare the adjacency to be down only if no OSPF
       unicast packets or no OSPF packets sent to AllSPFRouters over a
       point-to-point link are received over that adjacency for a period
       equaling or exceeding the RouterDeadInterval.  The reason for not
       recommending this proposal in conjunction with Recommendation 1
       is to avoid potential undesirable side effects.  One such effect
       is the delay in discovering the down status of an adjacency in a
       case where no high priority Hello packets are being received but
       the inactivity timer is being reset by other stale packets in the
       low priority queue.

   (3) Use an exponential backoff algorithm for determining the value of
       the LSA retransmission interval (RxmtInterval).  Let R(i)
       represent the RxmtInterval value used during the i-th
       retransmission of an LSA.  Use the following algorithm to compute
       R(i).

                    R(1) = Rmin
                    R(i+1) = Min(KR(i),Rmax)  for i>=1

       where K, Rmin, and Rmax are constants and the function Min(.,.)
       represents the minimum value of its two arguments.  Example
       values for K, Rmin, and Rmax may be 2, 5, and 40 seconds,
       respectively.  Note that the example value for Rmin, the initial
       retransmission interval, is the same as the sample value of
       RxmtInterval in [Ref1].

       This recommendation is motivated by the observation that during a
       network congestion event caused by control messages, a major
       source for sustaining the congestion is the repeated
       retransmission of LSAs.  The use of an exponential backoff
       algorithm for the LSA retransmission interval reduces the rate of
       LSA retransmissions while the network experiences congestion
       (during which it is more likely that multiple retransmissions of
       the same LSA would happen).  This in turn helps the network get
       out of the congested state.

   (4) Implicit Congestion Detection and Action Based on That:  If there
       is control message congestion at a router, its neighbors do not
       know about that explicitly.  However, they can implicitly detect
       it based on the number of unacknowledged LSAs to this router.  If
       this number exceeds a certain "high-water mark", then the rate at
       which LSAs are sent to this router should be reduced
       progressively using an exponential backoff mechanism but not
       below a certain minimum rate.  At a future time, if the number of
       unacknowledged LSAs to this router falls below a certain "low-
       water mark", then the rate of sending LSAs to this router should

       be increased progressively, again using an exponential backoff
       mechanism but not above a certain maximum rate.  The whole
       algorithm is given below.  Note that this algorithm is to be
       applied independently to each neighbor and only for unicast LSAs
       sent to a neighbor or LSAs sent to AllSPFRouters over a point-
       to-point link.

       Let,
       U(t) = Number of unacknowledged LSAs to neighbor at time t.
       H = A high-water mark (in units of number of unacknowledged
           LSAs).
       L = A low-water mark (in units of number of unacknowledged LSAs).
       G(t) = Gap between sending successive LSAs to neighbor at time t.
       F = The factor by which the above gap is to be increased during
           congestion and decreased after coming out of congestion.
       T = Minimum time that has to elapse before the existing gap
           is considered for change.
       Gmin = Minimum allowed value of gap.
       Gmax = Maximum allowed value of gap.

       The equation below shows how the gap is to be changed after a
       time T has elapsed since the last change:
                 _
                |
                | Min(FG(t),Gmax) if U(t+T) > H
       G(t+T) = | G(t) if H >= U(t+T) >= L
                | Max(G(t)/F,Gmin) if U(t+T) < L
                |_

       Min(.,.) and Max(.,.) represent the minimum and maximum values of
       the two arguments, respectively.

       Example values for the various parameters of the algorithm are as
       follows: H = 20, L = 10, F = 2, T = 1 second, Gmin = 20 ms, Gmax
       = 1 second.

       Recommendations 3 and 4 both slow down LSAs to congested
       neighbors based on implicitly detecting the congestion, but they
       have important differences.  Recommendation 3 progressively slows
       down successive retransmissions of the same LSA, whereas
       Recommendation 4 progressively slows down all LSAs (new or
       retransmission) to a congested neighbor.

   (5) Throttling Adjacencies to Be Brought Up Simultaneously:  If a
       router tries to bring up a large number of adjacencies to its
       neighbors simultaneously, then that may cause severe congestion
       due to database synchronization and LSA flooding activities.  It
       is recommended that during such a situation no more than "n"

       adjacencies should be brought up simultaneously.  Once a subset
       of adjacencies has been brought up successfully, newer
       adjacencies may be brought up as long as the number of
       simultaneous adjacencies being brought up does not exceed "n".
       The appropriate value of "n" would depend on the router
       processing power, total bandwidth available for control plane
       traffic, and propagation delay.  The value of "n" should be
       configurable.

       In the presence of throttling, an important issue is the order in
       which adjacencies are to be formed.  We recommend a First Come
       First Served (FCFS) policy based on the order in which the
       request for adjacency formation arrives.  Requests may either be
       from neighbors or self-generated.  Among the self-generated
       requests, a priority list may be used to decide the order in
       which the requests are to be made.  However, once an adjacency
       formation process starts it is not to be preempted except for
       unusual circumstances such as errors or time-outs.

In some of the recommendations above, we refer to point-to-point links. Those references should also include cases where a broadcast network is to be treated as a point-to-point connection from the standpoint of IP routing [Ref5]

3. Security Considerations

This memo does not create any new security issues for the OSPF protocol.

4. Acknowledgments

We would like to acknowledge the support and helpful comments from OSPF WG chairs Rohit Dube, Acee Lindem, and John Moy; Routing Area directors Alex Zinin and Bill Fenner; and IESG reviewers. We acknowledge Vivek Dube, Mitchell Erblich, Mike Fox, Tony Przygienda, and Krishna Rao for comments on previous versions of the document. We also acknowledge Margaret Chiosi, Elie Francis, Jeff Han, Beth Munson, Roshan Rao, Moshe Segal, Mike Wardlow, and Pat Wirth for collaboration and encouragement in our scalability improvement efforts for Link State Protocol-based networks.

5. Normative References

[Ref1] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [Ref2]  Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6", RFC
           2740, December 1999.

6. Informative References

   [Ref3]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
           (TE) Extensions to OSPF Version 2", RFC 3630, September 2003.

   [Ref4]  C. Alaettinoglu, V. Jacobson and H. Yu, "Towards Millisecond
           IGP Convergence", Work in Progress.

   [Ref5]  N. Shen, A. Lindem, J. Yuan, A. Zinin, R. White and S.
           Previdi, "Point-to-point operation over LAN in link-state
           routing protocols", Work in Progress.

   [Ref6]  Pappalardo, D., "AT&T, customers grapple with ATM net
           outage", Network World, February 26, 2001.

   [Ref7]  "AT&T announces cause of frame-relay network outage," AT&T
           Press Release, April 22, 1998.

   [Ref8]  Cholewka, K., "MCI Outage Has Domino Effect", Inter@ctive
           Week, August 20, 1999.

   [Ref9]  Jander, M., "In Qwest Outage, ATM Takes Some Heat", Light
           Reading, April 6, 2001.

   [Ref10] A. Zinin and M. Shand, "Flooding Optimizations in Link-State
           Routing Protocols", Work in Progress.

   [Ref11] Pillay-Esnault, P., "OSPF Refresh and Flooding Reduction in
           Stable Topologies", RFC 4136, July 2005.

   [Ref12] G. Ash, G. Choudhury, V. Sapozhnikova, M. Sherif, A. Maunder,
           V. Manral, "Congestion Avoidance & Control for OSPF
           Networks", Work in Progress.

   [Ref13] G. Choudhury, G. Ash, V. Manral, A. Maunder and V.
           Sapozhnikova, "Prioritized Treatment of Specific OSPF Packets
           and Congestion Avoidance: Algorithms and Simulations", AT&T
           Technical Report, August 2003.

   [Ref14] Nichols, K., Blake, S., Baker, F., and D. Black, "Definition
           of the Differentiated Services Field (DS Field) in the IPv4
           and IPv6 Headers", RFC 2474, December 1998.

Appendix A. LSA Storm: Causes and Impact

An LSA storm may be initiated due to many reasons. Here are some examples:

   (a) one or more link failures due to fiber cuts,

   (b) one or more router failures for some reason, e.g., software crash
       or some type of disaster (including power outage) in an office
       complex hosting many routers,

   (c) link/router flapping,

   (d) requirement of taking down and later bringing back many routers
       during a software/hardware upgrade,

   (e) near synchronization of the periodic 1800-second LSA refreshes of
       a subset of LSAs,

   (f) refresh of all LSAs in the system during a change in software
       version,

   (g) injecting a large number of external routes to OSPF due to a
       procedural error,

   (h) Router ID changes causing a large number of LSA re-originations
       (possibly LSA purges as well depending on the implementation).

In addition to the LSAs originated as a direct result of link/router failures, there may be other indirect LSAs as well. One example in MPLS networks is traffic engineering LSAs [Ref3] originated at other links as a result of significant changes in reserved bandwidth. These result from rerouting of Label Switched Paths (LSPs) that went down during the link/router failure. The LSA storm causes high CPU and memory utilization at the router processor causing incoming packets to be delayed or dropped. Delayed acknowledgments (beyond the retransmission timer value) results in retransmissions, and delayed Hello packets (beyond the Router-Dead interval) results in links being declared down. A trunk-down event causes router LSA origination by its end-point routers. If traffic engineering LSAs are used for each link, then that type of LSA would also be originated by the end-point routers and potentially elsewhere as well due to significant changes in reserved bandwidths at other links caused by the failure and reroute of LSPs originally using the failed trunk. Eventually, when the link recovers that would also trigger additional router LSAs and traffic engineering LSAs. The retransmissions and additional LSA originations result in further CPU and memory usage, essentially causing a positive feedback loop. We define the LSA storm size as the number of LSAs in the original storm, not counting any additional LSAs resulting from the feedback loop described above. If the LSA storm is too large, then the positive feedback loop mentioned above may be large enough to indefinitely sustain a large CPU and memory utilization at many routers in the network, thereby driving the network to an unstable state. In the past, network outage events have been reported in IP and ATM networks using link-state protocols such as OSPF, Intermediate System to Intermediate System (IS-IS), Private Network- Network Interface (PNNI), or some proprietary variants. See for example [Ref6-Ref9]. In many of these examples, large-scale flooding of LSAs or other similar control messages (either naturally or triggered by some bug or inappropriate procedure) have been partly or fully responsible for network instability and outage.

In [Ref13], a simulation model is used to show that there is a certain LSA storm size threshold above which the network may show unstable behavior caused by a large number of retransmissions, link failures due to missed Hello packets, and subsequent link recoveries. It is also shown that the LSA storm size causing instability may be substantially increased by providing prioritized treatment to Hello and LSA Acknowledgment packets and by using an exponential backoff algorithm for determining the LSA retransmission interval. If it is not possible to prioritize Hello packets, then resetting the inactivity timer on receiving any valid OSPF packets can also provide the same benefit. Furthermore, if we prioritize Hello packets, then even when the network operates somewhat above the stability threshold, links are not declared down due to missed Hellos. This implies that even though there is control plane congestion due to many retransmissions, the data plane stays up and no new LSAs are originated (besides the ones in the original storm and the refreshes). These observations support the first three recommendations in Section 2. The authors of this document have also done simulations to verify that the other recommendations in Section 2 help avoid congestion and allow a graceful exit from a congested state.

One might argue that the scalability issue of large networks should be solved solely by dividing the network hierarchically into multiple areas so that flooding of LSAs remains localized within areas. However, this approach increases the network management and design complexity and may result in less optimal routing between areas. Also, Autonomous System External (ASE) LSAs are flooded throughout the AS, and it may be a problem if there are large numbers of them. Furthermore, a large number of summary LSAs may need to be flooded across areas, and their numbers would increase significantly if multiple Area Border Routers are employed for the purpose of reliability. Thus, it is important to allow the network to grow towards as large a size as possible under a single area.

The recommendations in the document are synergistic with a broader set of scalability and stability improvement proposals. [Ref10] proposes flooding overhead reduction in case more than one interface goes to the same neighbor. [Ref11] proposes a mechanism for greatly reducing LSA refreshes in stable topologies.

[Ref12] proposes a wide range of congestion control and failure recovery mechanisms (some of those ideas are covered in this document, but [Ref12] has other ideas not covered here).

Appendix B. List of Variables and Values

   F    = The factor by which the gap between sending successive LSAs to
          a neighbor is to be increased during congestion and decreased
          after coming out of congestion (used in Recommendation 4).
          Example value is 2.

   G(t) = Gap between sending successive LSAs to a neighbor at time t
          (used in Recommendation 4).

   Gmax = Maximum allowed value of gap between sending successive LSAs
          to a neighbor (used in Recommendation 4).  Example value is 1
          second.

   Gmin = Minimum allowed value of gap between sending successive LSAs
          to a neighbor (used in Recommendation 4).  Example value is 20
          ms.

   H    = A high-water mark (in units of number of unacknowledged LSAs).
          Exceeding this mark would trigger a potential increase in the
          gap between sending successive LSAs to a neighbor.  (used in
          Recommendation 4).  Example value is 20.

   K    = A multiplicative constant used in increasing the RxmtInterval
          value used during successive retransmissions of the same LSA
          (used in Recommendation 3).  Example value is 2.

   L    = A low-water mark (in units of number of unacknowledged LSAs)
          Dropping below this mark would trigger a potential decrease in
          the gap between sending successive LSAs to a neighbor.  (used
          in Recommendation 4).  Example value is 10.

   n    = Upper limit on the number of adjacencies to be brought up
          simultaneously (used in Recommendation 5).

   R(i) = RxmtInterval value used during the i-th retransmission of an
          LSA (used in Recommendation 3).

   Rmax = The maximum allowed value of RxmtInterval (used in
          Recommendation 3).  Example value is 40 seconds.

   Rmin = The minimum allowed value of RxmtInterval (used in
          Recommendation 3).  Example value is 5 seconds.

   T    = Minimum time that has to elapse before the existing gap
          between sending successive LSAs to a neighbor is considered
          for change (used in Recommendation 4).  Example value is 1
          second.

   U(t) = Number of unacknowledged LSAs to a neighbor at time t (used in
          Recommendation 4).

Appendix C. Other Recommendations and Suggestions

   (1) Explicit Marking:  In Section 2, we recommended that OSPF packets
       be classified to "high" and "low" priority classes based on
       examining the OSPF packet header.  In some cases (particularly in
       the receiver), this examination may be computationally costly.
       An alternative would be the use of different TOS/Precedence field
       settings for the two priority classes.  [Ref1] recommends setting
       the TOS field to 0 and the Precedence field to 6 for all OSPF
       packets.  We recommend this same setting for the "low" priority
       OSPF packets and a different setting for the "high" priority OSPF
       packets in order to be able to classify them separately without
       having to examine the OSPF packet header.  Two examples are given
       below:

       Example 1: For "low" priority packets, set TOS field to 0 and
                  Precedence field to 6, and for "high" priority packets
                  set TOS field to 4 and Precedence field to 6.

       Example 2: For "low" priority packets, set TOS field to 0 and
                  Precedence field to 6, and for "high" priority packets
                  set TOS field to 0 and Precedence field to 7.

Note that the TOS/Precedence bits have been redefined by Diffserv (RFC 2474, [Ref14]). Also note that the different TOS/Precedence field settings suggested above only need to be agreed among the systems on the link. This recommendation is not needed to be followed if it is easy to examine the OSPF packet header and thereby separately classify "high" and "low" priority packets.

   (2) Further Prioritization of OSPF Packets: Besides the packets
       designated as "high" priority in Recommendation 1 of Section 2,
       there may be a need for further priority separation among the
       "low" priority OSPF packets.  We recommend the use of three
       priority classes: "high", "medium" and "low".  While receiving a
       packet from a neighbor and while transmitting a packet to a
       neighbor, try to process a "high priority" packet ahead of
       "medium" and "low" priority packets and a "medium" priority
       packet ahead of "low priority" packets.  The "high" priority
       packets are as designated in Recommendation 1 of Section 2.  We
       provide below two candidate examples for "medium" priority
       packets.  All OSPF packets not designated as "high" or "medium"
       priority are "low" priority.  If Cryptographic Authentication
       (AuType = 2) is used (as specified in [Ref1]), then prioritized
       treatment is to be provided only at the receiver and after
       security processing, but not at the transmitter since that may
       cause packets to arrive out of sequence and violate the
       requirements of "Autype = 2".

       One example of "medium" priority packet is the Database
       Description (DBD) packet from a slave (during the database
       synchronization process) that is used as an acknowledgment.

       A second example is an LSA carrying intra-area topology change
       information (this may trigger SPF calculation and rerouting of
       Label Switched Paths, so fast processing of this packet may
       improve OSPF/Label Distribution Protocol (LDP) convergence
       times).  However, if the processing cost of identifying and
       separately queueing the LSA in this example is deemed to be high,
       then the implementer may decide not to do it.

   (3) Processing a Large Number of LSA Purges: Occasionally, some
       events in the network, such as router ID changes, may result in a
       large number of LSA re-originations and LSA purges.  In such a
       scenario, one may consider processing LSAs in different order,
       e.g., processing LSA purges ahead of LSA originations.  We,
       however, do not recommend out-of-order LSA processing for several
       reasons.  First, detecting the LSA type ahead of queueing may be
       computationally expensive.  Out-of-order processing may also
       cause subtle bugs.  We do not want to recommend a major change in
       the LSA processing paradigm for a relatively rare event such as
       router ID change.  However, a router with a changing ID may flush
       the old LSAs gradually without causing a storm.

Contributing Authors and Their Addresses

In addition to the editor, several people contributed to this document. The names and contact information of all authors are given below.

   Anurag S. Maunder
   Erlang Technology
   2880 Scott Boulevard
   Santa Clara, CA 95052
   USA

Phone: (408) 420-7617 EMail: anuragm@erlangtech.com

   Gerald R. Ash
   AT&T
   Room D5-2A01
   200 Laurel Avenue
   Middletown, NJ, 07748
   USA

Phone: (732) 420-4578 EMail: gash@att.com

   Vishwas Manral
   Sinett Corp,
   2/1 Embassy Icon Annex,
   Infantry Road,
   Bangalore 560 001
   India

Phone: +91-(805)-137-7023 EMail: vishwas@sinett.com

   Vera D. Sapozhnikova
   AT&T
   Room C5-2C29
   200 Laurel Avenue
   Middletown, NJ, 07748
   USA

Phone: (732) 420-2653 EMail: sapozhnikova@att.com

Editor's Address

   Gagan L. Choudhury
   AT&T
   Room D5-3C21
   200 Laurel Avenue
   Middletown, NJ, 07748
   USA

Phone: (732) 420-3721 EMail: gchoudhury@att.com

Full Copyright Statement

Copyright © 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.

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 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.

Acknowledgement

Funding for the RFC Editor function is currently provided by the Internet Society.