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Network Working Group                                       T. PrzygiendaRequest for Comments: 2844                                          SiaraCategory: Experimental                                            P. Droz                                                                  R. Haas                                                                      IBM                                                                 May 2000OSPF over ATM and Proxy-PARStatus of this Memo   This memo defines an Experimental Protocol for the Internet   community.  It does not specify an Internet standard of any kind.   Discussion and suggestions for improvement are requested.   Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2000).  All Rights Reserved.Abstract   This memo specifies, for OSPF implementors and users, mechanisms   describing how the protocol operates in ATM networks over PVC and SVC   meshes with the presence of Proxy-PAR. These recommendations require   no protocol changes and allow simpler, more efficient and cost-   effective network designs. It is recommended that OSPF   implementations should be able to support logical interfaces, each   consisting of one or more virtual circuits and used either as   numbered logical point-to-point links (one VC), logical NBMA networks   (more than one VC) or Point-to-MultiPoint networks (more than one   VC), where a solution simulating broadcast interfaces is not   appropriate. PAR can help distribute across the ATM cloud   configuration setup and changes of such interfaces when OSPF capable   routers are (re-)configured.  Proxy-PAR can in turn be used to   exchange this information between the ATM cloud and the routers   connected to it.1 Introduction   Proxy-PAR and PAR have been accepted as standards by the ATM Forum in   January 1999 [1]. A more complete overview of Proxy-PAR than in the   section below is given in [2].Przygienda, et al.            Experimental                      [Page 1]

RFC 2844              OSPF over ATM and Proxy-PAR               May 20001.1 Introduction to Proxy-PAR   Proxy-PAR [1] is an extension that allows different ATM attached   devices (like routers) to interact with PAR-capable switches and to   query information about non-ATM services without executing PAR   themselves. The Proxy-PAR client side in the ATM attached device is   much simpler in terms of implementation complexity and memory   requirements than a complete PAR protocol stack (which includes the   full PNNI [3] protocol stack) and should allow easy implementation,   e.g. in existing IP routers.  In addition, clients can use Proxy-PAR   to register the various non-ATM services and protocols they support.   Proxy PAR has consciously been omitted as part of ILMI [4] due to the   complexity of PAR information passed in the protocol and the fact   that it is intended for integration of non-ATM protocols and services   only. A device that executes Proxy-PAR does not necessarily need to   execute ILMI or UNI signaling, although this normally will be the   case.   The protocol in itself does not specify how the distributed service   registration and data delivered to the client is supposed to drive   other protocols. Hence OSPF routers, for instance, that find   themselves through Proxy-PAR could use this information in a   Classical IP and ARP over ATM [5] fashion, forming a full mesh of   point-to-point connections to interact with each other to simulate   broadcast interfaces. For the same purpose, LANE [6] or MARS [7]   could be used. As a byproduct, Proxy-PAR could provide the ATM   address resolution for IP-attached devices, but such resolution can   be achieved by other protocols under specification at the IETF as   well, e.g. [8]. Last but not least, it should be mentioned here that   the protocol coexists with and complements the ongoing work in IETF   on server detection via ILMI extensions [9,10,11].1.1.1 Proxy-PAR Scopes   Any information registered through Proxy-PAR is flooded only within a   defined scope that is established during registration and is   equivalent to the PNNI routing level. As no assumption can be made   about the information distributed (e.g. IP addresses bound to NSAPs   are not assumed to be aligned with them in any respect such as   encapsulation or functional mapping), it cannot be summarized. This   makes a careful handling of scopes necessary to preserve the   scalability. More details on the usage of scope can be found in [2].Przygienda, et al.            Experimental                      [Page 2]

RFC 2844              OSPF over ATM and Proxy-PAR               May 20001.2 Introduction to OSPF   OSPF (Open Shortest Path First) is an Interior Gateway Protocol (IGP)   and described in [12] from which most of the following paragraphs has   been taken almost literally. OSPF distributes routing information   between routers belonging to a single Autonomous System. The OSPF   protocol is based on link-state or SPF technology. It was developed   by the OSPF working group of the Internet Engineering Task Force. It   has been designed expressly for the TCP/IP internet environment,   including explicit support for IP subnetting, and the tagging of   externally-derived routing information. OSPF also utilizes IP   multicast when sending/receiving the updates. In addition, much work   has been done to produce a protocol that responds quickly to topology   changes, yet involves small amounts of routing protocol traffic.   To cope with the needs of NBMA and demand-circuit-capable networks   such as Frame Relay or X.25, [13] has been made available. It   standardizes extensions to the protocol that allow efficient   operation over on-demand circuits.   OSPF supports three types of networks today:      +  Point-to-point networks: A network that joins a single pair of         routers. Point-to-point networks can either be numbered or         unnumbered. In the latter case the interfaces do not have IP         addresses nor masks. Even when numbered, both sides of the link         do not have to agree on the IP subnet.      +  Broadcast networks: Networks supporting many (more than two)         attached routers, together with the capability of addressing a         single physical message to all of the attached routers         (broadcast). Neighboring routers are discovered dynamically on         these networks using the OSPF Hello Protocol. The Hello         Protocol itself takes advantage of the broadcast capability.         The protocol makes further use of multicast capabilities, if         they exist. An Ethernet is an example of a broadcast network.      +  Non-broadcast networks: Networks supporting many (more than         two) attached routers, but having no broadcast capability.         Neighboring routers are maintained on these nets using OSPF's         Hello Protocol.  However, due to the lack of broadcast         capability, some configuration information is necessary for the         correct operation of the Hello Protocol. On these networks,         OSPF protocol packets that are normally multicast need to be         sent to each neighboring router, in turn. An X.25 Public Data         Network (PDN) is an example of a non-broadcast network.Przygienda, et al.            Experimental                      [Page 3]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000         OSPF runs in one of two modes over non-broadcast networks. The         first mode, called non-broadcast multi-access (NBMA), simulates         the operation of OSPF on a broadcast network. The second mode,         called Point-to-MultiPoint, treats the non-broadcast network as         a collection of point-to-point links. Non-broadcast networks         are referred to as NBMA networks or Point-to-MultiPoint         networks, depending on OSPF's mode of operation over the         network.2 OSPF over ATM2.1 Model   Contrary to broadcast-simulation-based solutions such as LANE [6] or   Classical IP and ARP over ATM [5], this document elaborates on how to   handle virtual OSPF interfaces over ATM such as NBMA, Point-to-   MultiPoint or point-to-point and allow for their auto-configuration   in the presence of Proxy-PAR. One advantage is the circumvention of   server solutions that often present single points of failure or hold   large amounts of configuration information.   The other main benefit is the capability of executing OSPF on top of   NBMA and Point-to-MultiPoint ATM networks, and still benefit from the   automatic discovery of OSPF neighbors. As opposed to broadcast   networks, broadcast-simulation-based networks (such as LANE or   Classical IP and ARP over ATM), and point-to-point networks, where an   OSPF router dynamically discovers its neighbors by sending Hello   packets to the All-SPFRouters multicast address, this is not the case   on NBMA and Point-to-MultiPoint networks. On NBMA networks, the list   of all other attached routers to the same NBMA network has to be   manually configured or discovered by some other means: Proxy-PAR   allows this configuration to be automated.  Also on Point-to-   MultiPoint networks, the set of routers that are directly reachable   can either be manually configured or dynamically discovered by   Proxy-PAR or mechanisms such as Inverse ATMARP. In an ATM network,   (see 8.2 in [5]) Inverse ATMARP can be used to discover the IP   address of the router at the remote end of a given PVC, whether or   not its ATM address is known. But Inverse ATMARP does not return, for   instance, whether the remote router is running OSPF, unlike Proxy-   PAR.   Parallel to [14], which describes the recommended operation of OSPF   over Frame Relay networks, a similar model is assumed where the   underlying ATM network can be used to model single VCs as point-to-   point interfaces or collections of VCs as non-broadcast interfaces,   whether in NBMA or Point-to-MultiPoint mode. Such a VC or collection   of VCs is called a logical interface and specified through its type   (either point-to-point, NBMA or Point-to-MultiPoint), VPN ID (thePrzygienda, et al.            Experimental                      [Page 4]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000   Virtual Private Network to which the interface belongs), address and   mask. Layer 2 specific configurations such as the address resolution   method, class and quality of service of circuits used, and others,   must also be included. As a logical consequence thereof, a single,   physical interface could encompass multiple IP subnets or even   multiple VPNs. Contrary to layer 2 and IP addressing information,   when running Proxy-PAR, most of the OSPF information needed to   operate such a logical interface does not have to be configured into   routers statically but can be provided through Proxy-PAR queries.   This allows much more dynamic configuration of VC meshes in OSPF   environments than, for example, Frame Relay solutions do.   Proxy-PAR queries can also be issued with a subnet address set to   0.0.0.0, instead of a specific subnet address. This type of query   returns information on all OSPF routers available in all subnets   within the scope specified in the query. This can be used for   instance when the IP addressing information has not been configured.2.2 Configuration of OSPF interfaces with Proxy-PAR   To achieve the goal of simplification of VC mesh reconfiguration,   Proxy-PAR allows the router to learn automatically most of the   configuration that has to be provided to OSPF. Non-broadcast and   point-to-point interface information can be learned across an ATM   cloud as described in the ongoing sections. It is up to the   implementation to possibly allow for a mixture of Proxy-PAR   autoconfiguration and manual configuration of neighbor information.   Moreover, manual configuration could, for instance, override or   complement information derived from a Proxy-PAR client. In addition,   OSPF extensions to handle on-demand circuits [13] can be used to   allow the graceful tearing down of VCs not carrying any OSPF traffic   over prolonged periods of time.  The various interactions are   described in sections2.2.1,2.2.2 and2.2.3.   Even after autoconfiguration of interfaces has been provided, the   problem of VC setups in an ATM network is unsolved because none of   the normally used mechanisms such as Classical IP and ARP over ATM   [5] or LANE [6] are assumed to be present.Section 2.5 describes the   behavior of OSPF routers necessary to allow for router connectivity.2.2.1 Autoconfiguration of Non-Broadcast Multiple-Access (NMBA)      Interfaces   Proxy-PAR allows the autoconfiguation of the list of all routers   residing on the same IP network in the same VPN by simply querying   the Proxy-PAR server. Each router can easily obtain the list of all   OSPF routers on the same subnet with their router priorities and   corresponding ATM addresses. This is the precondition for OSPF toPrzygienda, et al.            Experimental                      [Page 5]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000   work properly across such logical NBMA interfaces. Note that this   member list, when learned through Proxy-PAR queries, can dynamically   change with PNNI (in)stability and general ATM network behavior.   Relying on an OSPF mechanism to discover a lack of reachability in   the overlaying logical IP network could alleviate the risk of   thrashing DR elections and excessive information flooding. Once the   DR election has been completed and the router has not been elected DR   or BDR, an implementation of [13] can ignore the fact that all   routers on the specific NBMA subnet are available in its   configuration because it only needs to maintain VCs to the DR and   BDR. Note that this information can serve other purposes, such as the   forwarding of data packets (seesection 2.4).   Traditionally, router configuration for a NBMA network provides the   list of all neighboring routers to allow for proper protocol   operation. For stability purposes, the user may choose to provide a   list of neighbors through such static means but also enable the   operation of Proxy-PAR protocol to complete the list.  It is left up   to specific router implementations to determine whether to use the   manual configuration in addition to the information provided by   Proxy-PAR, to use the manual configuration to filter dynamic   information, or whether a concurrent mode of operation is prohibited.   In any case it should be obvious that allowing for more flexibility   may facilitate operation but provides more possibilities for   misconfiguration as well.2.2.2 Autoconfiguration of Point-to-MultiPoint Interfaces   Point-to-MultiPoint interfaces in ATM networks only make sense if no   VCs can be set up dynamically because an SVC-capable ATM network   normally presents a NBMA cloud to OSPF. This is for example the case   if OSPF executes over a network composed of a partial PVC or SPVC   mesh or predetermined SVC meshes. Such a network could be modeled   using the Point-to-MultiPoint OSPF interface and the neighbor   detection could be provided by Proxy-PAR or other means. In the   Proxy-PAR case the router queries for all OSPF routers on the same   network in the same VPN but it installs in the interface   configuration only routers that are already reachable through   existing PVCs. The underlying assumption is that a router knows the   remote ATM address of a PVC and can compare it with appropriate   Proxy-PAR registrations. If the remote ATM address of the PVC is   unknown, it can be discovered by such mechanisms as Inverse ARP [15].Przygienda, et al.            Experimental                      [Page 6]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000   Proxy-PAR provides a true OSPF neighbor detection mechanism, whereas   a mechanism like Inverse ARP only returns addresses of directly   reachable routers (which are not necessarily running OSPF), in the   Point-to-Multi-Point environment.2.2.3 Autoconfiguration of Numbered Point-to-Point Interfaces   OSPF point-to-point links do not necessarily have an IP address   assigned and even if they do, the mask is undefined. As a   precondition to successfully register a service with Proxy-PAR, an IP   address and a mask are required. Therefore, if a router desires to   use Proxy-PAR to advertise the local end of a point-to-point link to   the router with which it intends to form an adjacency, an IP address   has to be provided as well as a netmask set or a default of   255.255.255.252 (this gives as the default case a subnet with two   routers on it) assumed. To allow the discovery of the remote end of   the interface, IP address of the remote side has to be provided and a   netmask set or a default of 255.255.255.252 assumed. Obviously the   discovery can only be successful when both sides of the interface are   configured with the same network mask and are within the same IP   network. The situation where more than two possible neighbors are   discovered through queries and the interface type is set to point-   to-point presents a configuration error.   Sending multicast Hello packets on the point-to-point links allows   OSPF neighbors to be discovered automatically. On the other hand,   using Proxy-PAR instead avoids sending Hello messages to routers that   are not necessarily running OSPF.2.2.4 Autoconfiguration of Unnumbered Point-to-Point Interfaces   For reasons given in [14], the use of unnumbered point-to-point   interfaces with Proxy-PAR is not a very attractive alternative   because the lack of an IP address prevents efficient registration and   retrieval of configuration information. Relying on the numbering   method based on MIB entries generates conflicts with the dynamic   nature of creation of such entries and is beyond the scope of this   work.2.3 Registration of OSPF interfaces with Proxy-PAR   To allow other routers to discover an OSPF interface automatically,   the IP address, mask, Area ID, interface type and router priority   information given must be registered with the Proxy-PAR server at an   appropriate scope. A change in any of these parameters has to force a   reregistration with Proxy-PAR.Przygienda, et al.            Experimental                      [Page 7]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000   It should be emphasized here that because the registration   information can be used by other routers to resolve IP addresses   against NSAPs as explained insection 2.4, the entire IP address of   the router must be registered. It is not sufficient to indicate the   subnet up to the mask length; all address bits must be provided.2.3.1 Registration of Non-Broadcast Multiple-Access Interfaces   For an NBMA interface the appropriate parameters are available and   can be registered through Proxy-PAR without further complications.2.3.2 Registration of Point-to-Multipoint Interfaces   In the case of a Point-to-MultiPoint interface the router registers   its information in the same fashion as in the NBMA case, except that   the interface type is modified accordingly.2.3.3 Registration of Numbered Point-to-Point Interfaces   In the case of point-to-point numbered interfaces the address mask is   not specified in the OSPF configuration. If the router has to use   Proxy-PAR to advertise its capability, a mask must be defined or a   default value of 255.255.255.252 used.2.3.4 Registration of Unnumbered Point-to-Point Interfaces   Owing to the lack of a configured IP address and difficulties   generated by this fact as described earlier, registration of   unnumbered point-to-point interfaces is not covered in this document.2.4 IP address to NSAP Resolution Using Proxy-PAR   As a byproduct of Proxy-PAR presence, an OSPF implementation could   use the information in registrations for the resolution of IP   addresses to ATM NSAPs on a subnet without having to use static data   or mechanisms such as ATMARP [5]. This again should allow a drastic   simplification of the number of mechanisms involved in operating OSPF   over ATM to provide an IP overlay.   From a system perspective, the OSPF component, the Proxy-PAR client,   the IP to NSAP address resolution table, and the ATM circuit manager   can be depicted as in Figure 1. Figure 1 shows an example of   component interactions triggered by a Proxy-PAR query from the   Proxy-PAR client.Przygienda, et al.            Experimental                      [Page 8]

RFC 2844              OSPF over ATM and Proxy-PAR               May 20002.5 Connection Setup Mechanisms   This section describes the OSPF behavior in an ATM network under   various assumptions in terms of signaling capabilities and preset   connectivity.2.5.1 OSPF in PVC Environments   In environments where only partial PVCs (or SPVCs) meshes are   available and modeled as Point-to-MultiPoint interfaces, the routers   see reachable routers through autodiscovery provided by Proxy-PAR.   This leads to expected OSPF behavior. In cases where a full mesh of   PVCs is present, such a network should preferably be modeled as NBMA.   Note that in such a case, PVCs failures will translate into not-so-   obvious routing failures.        __________                      _________       |          |                    |         |       |   OSPF   |<-------------------|Proxy-PAR|<---(Proxy-PAR query)       |__________|  notify            | client  |            ^        neighbor changes  |_________|            |                               |   send and |                               | maintain Proxy-PAR   receive  |                               | entries in table   OSPF msg |                               |            |                               |            |                               |        ____V____                       ____V_____       |   ATM   |                     |          |       | circuit |-------------------->|IP to NSAP|       | manager | check               |  table   |       |_________| IP to NSAP bindings |__________|   Figure 1: System perspective of typical components interactions.Przygienda, et al.            Experimental                      [Page 9]

RFC 2844              OSPF over ATM and Proxy-PAR               May 20002.5.2 OSPF in SVC Environments          +           +                             +          |   +---+   |                             |   +--+   |---|RTA|---|          +-------+          |   +--+   |H1|---|   +---+   |          | ATM   |          |---|H2|   +--+   |           |   +---+  | Cloud |  +---+   |   +--+          |LAN Y      |---|RTB|-------------|RTC|---|          +           |   +---+  | PPAR  |  +---+   |                      +          +-------+          +     Figure 2: Simple topology with Router B and Router C operating               across NBMA ATM interfaces with Proxy-PAR.   In SVC-capable environments the routers can initiate VCs after having   discovered the appropriate neighbors, preferably driven by the need   to send data such as Hello packets. This can lead to race conditions   where both sides can open a VC simultaneously. It is generally   desirable to avoid wasting this valuable resource: if the router with   lower IP address (i.e., the IP address of the OSPF interface   registered with Proxy-PAR) detects that the VC initiated by the other   side is bidirectional, it is free to close its own VC and use the   detected one. Note that this either requires the OSPF implementation   to be aware of the VCs used to send and receive Hello messages, or   the component responsible of managing VCs to be aware of the usage of   particular VCs.   Observe that this behavior operates correctly in case OSPF over   Demand Circuits extensions are used [13] over SVC capable interfaces.   Most of the time, it is possible to avoid the setup of redundant VCs   by delaying the sending of the first OSPF Hello from the router with   the lower IP address by an amout of time greater than the interval   between the queries from the Proxy-PAR client to the server. Chances   are that the router with the higher IP address opens the VC (or use   an already existing VC) and sends the OSPF Hello first if its   interval between queries is shorter than the Hello delay of the   router with the lower IP address. As this interval can vary depending   on particular needs and implementations, the race conditions   described above can still be expected to happen, albeit presumably   less often.   The existence of VCs used for OSPF exchanges is orthogonal to the   number and type of VCs the router chooses to use within the logical   interface to forward data to other routers. OSPF implementations are   free to use any of these VCs (in case they are aware of their   existence) to send packets if their end points are adequate and must   accept Hello packets arriving on any of the VCs belonging to thePrzygienda, et al.            Experimental                     [Page 10]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000   logical interface even if OSPF operating on such an interface is not   aware of their existence. An OSPF implementation may ignore   connections being initiated by another router that has not been   discovered by Proxy-PAR. In any case, the OSPF implementation will   ignore a neighbor whose Proxy-PAR registration indicates that it is   not adjacent.   As an example consider the topology in Figure 2 where router RTB and   RTC are connected to a common ATM cloud offering Proxy-PAR services.   Assuming that RTB's OSPF implementation is aware of SVCs initiated on   the interface and that RTC only makes minimal use of Proxy-PAR   information, the following sequence could develop, illustrating some   of the cases described above:      1. RTC and RTB register with ATM cloud as Proxy-PAR capable and         discover each other as adjacent OSPF routers.      2. RTB sends a Hello, which forces it to establish a SVC         connection to RTC.      3. RTC sends a Hello to RTB, but disregards the already existing         VC and establishes a new VC to RTB to deliver the packet.      4. RTB sees a new bidirectional VC and, assuming here that RTC's         IP address is higher, closes the VC originated in step 2.      5. Host H1 sends data to H2 and RTB establishes a new data SVC         between itself and RTC.      6. RTB sends a Hello to RTC and decides to do so using the newly         establish data SVC. RTC must accept the Hello despite the         minimal implementation.3 Acknowledgments   Comments and contributions from several sources, especially Rob   Coltun, Doug Dykeman, John Moy and Alex Zinin are included in this   work.4 Security Considerations   Several aspects are to be considered in the context of the security   of operating OSPF over ATM and/or Proxy-PAR. The security of   registered information handed to the ATM cloud must be guaranteed by   the underlying PNNI protocol. The registration itself through Proxy-   PAR is not secured, and are thus appropriate mechanisms for further   study. However, even if the security at the ATM layer is not   guaranteed, OSPF security mechanisms can be used to verify thatPrzygienda, et al.            Experimental                     [Page 11]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000   detected neighbors are authorized to interact with the entity   discovering them.5 Bibliography   [1]  ATM Forum, "PNNI Augmented Routing (PAR) Version 1.0."  ATM        Forum af-ra-0104.000, January 1999.   [2]  Droz, P. and T. Przygienda, "Proxy-PAR",RFC 2843, May 2000.   [3]  ATM-Forum, "Private Network-Network Interface Specification        Version 1.0." ATM Forum af-pnni-0055.000, March 1996.   [4]  ATM-Forum, "Interim Local Management Interface, (ILMI)        Specification 4.0." ATM Forum af-ilmi-0065.000, September 1996.   [5]  Laubach, J., "Classical IP and ARP over ATM",RFC 2225, April        1998.   [6]  ATM-Forum, "LAN Emulation over ATM 1.0." ATM Forum af-lane-        0021.000, January 1995.   [7]  Armitage, G., "Support for Multicast over UNI 3.0/3.1 based ATM        Networks",RFC 2022, November 1996.   [8]  Coltun, R., "The OSPF Opaque LSA Option",RFC 2328, July 1998.   [9]  Davison, M., "ILMI-Based Server Discovery for ATMARP",RFC 2601,        June 1999.   [10] Davison, M., "ILMI-Based Server Discovery for MARS",RFC 2602,        June 1999.   [11] Davison, M., "ILMI-Based Server Discovery for NHRP",RFC 2603,        June 1999.   [12] Moy, J., "OSPF Version 2",RFC 2328, April 1998.   [13] Moy, J., "Extending OSPF to Support Demand Circuits",RFC 1793,        April 1995.   [14] deSouza, O. and M. Rodrigues, "Guidelines for Running OSPF Over        Frame Relay Networks",RFC 1586, March 1994.   [15] Bradley, A. and C. Brown, "Inverse Address Resolution Protocol",RFC 2390, September 1999.Przygienda, et al.            Experimental                     [Page 12]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000Authors' Addresses   Tony Przygienda   Siara Systems Incorporated   1195 Borregas Avenue   Sunnyvale, CA 94089   USA   EMail: prz@siara.com   Patrick Droz   IBM Research   Zurich Research Laboratory   Saumerstrasse 4   8803 Ruschlikon   Switzerland   EMail: dro@zurich.ibm.com   Robert Haas   IBM Research   Zurich Research Laboratory   Saumerstrasse 4   8803 Ruschlikon   Switzerland   EMail: rha@zurich.ibm.comPrzygienda, et al.            Experimental                     [Page 13]

RFC 2844              OSPF over ATM and Proxy-PAR               May 2000Full Copyright Statement   Copyright (C) The Internet Society (2000).  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   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 assigns.   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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Przygienda, et al.            Experimental                     [Page 14]