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Network Working Group                                           P. DrozRequest for Comments: 2843                                          IBMCategory: Informational                                   T. Przygienda                                                                  Siara                                                               May 2000Proxy-PARStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2000).  All Rights Reserved.Abstract   Proxy-PAR is a minimal version of PAR (PNNI Augmented Routing) that   gives ATM-attached devices the ability to interact with PNNI devices   without the necessity to fully support PAR. Proxy-PAR is designed as   a client/server interaction, of which the client side is much simpler   than the server side to allow fast implementation and deployment.   The purpose of Proxy-PAR is to allow non-ATM devices to use the   flooding mechanisms provided by PNNI for registration and automatic   discovery of services offered by ATM attached devices.  The first   version of PAR primarily addresses protocols available in IPv4. But   it also contains a generic interface to access the flooding of PNNI.   In addition, Proxy-PAR-capable servers provide filtering based on VPN   IDs [1], IP protocols and address prefixes. This enables, for   instance, routers in a certain VPN running OSPF to find OSPF   neighbors on the same subnet. The protocol is built using a   registration/query approach where devices can register their services   and query for services and protocols registered by other clients.1 Introduction   In June of 1996, the ATM Forum accepted the "Proxy-PAR contribution   as minimal subset of PAR" as a work item of the Routing and   Addressing (RA) working group, which was previously called the PNNI   working group [2].  The PAR [3] specification provides a detailed   description of the protocol including state machines and packet   formats.Droz & Przygienda            Informational                      [Page 1]

RFC 2843                       Proxy-PAR                        May 2000   The intention of this document is to provide general information   about Proxy-PAR. For the detailed protocol description we refer the   reader to [3].   Proxy-PAR is a protocol that allows various ATM-attached devices (ATM   and non-ATM devices) to interact with PAR-capable switches to   exchange information about non-ATM services without executing PAR   themselves. The client side is much simpler in terms of   implementation complexity and memory requirements than a complete PAR   instance. This should allow an easy implementation on existing IP   devices such as IP routers. Additionally, clients can use Proxy-PAR   to register various non-ATM services and the protocols they support.   The protocol has deliberately been omitted from ILMI [4] because of   the complexity of PAR information passed in the protocol and the fact   that it is intended for the integration of non-ATM protocols and   services only. A device executing Proxy-PAR does not necessarily need   to execute ILMI or UNI signalling, although this will normally be the   case.   The protocol does not specify how a client should make use of the   obtained information to establish connectivity. For example, OSPF   routers finding themselves through Proxy-PAR could establish a full   mesh of P2P VCs by means ofRFC2225 [5], or useRFC1793 [6] to   interact with each other.  LANE [7] or MARS [8] could be used for the   same purpose. It is expected that the guidelines defining how a   certain protocol can make use of Proxy-PAR should be produced by the   appropriate working group or standardization body responsible for the   particular protocol. An additional RFC [9] describing how to run OSPF   together with Proxy-PAR is published together with this document.   The protocol has the ability to provide ATM address resolution for   IP-attached devices, but such resolutions can also be achieved by   other protocols under specification in the IETF, e.g. [10]. Again,   the main purpose of the protocol is to allow the automatic detection   of devices over an ATM cloud in a distributed fashion, omitting the   usual pitfalls of server-based solutions. Last but not least, it   should be mentioned here as well that the protocol complements and   coexists with the work done in the IETF on server detection via ILMI   extensions [11,12,13].2 Proxy-PAR Operation and Interaction with PNNI   The protocol is asymmetric and consists of a discovery and   query/registration part. The discovery is very similar to the   existing PNNI Hello protocol and is used to initiate and maintain   communication between adjacent clients and servers. The registration   and update part execute after a Proxy-PAR adjacency has been   established. The client can register its own services by sendingDroz & Przygienda            Informational                      [Page 2]

RFC 2843                       Proxy-PAR                        May 2000   registration messages to the server. The client obtains information   it is interested in by sending query messages to the server. When the   client needs to change its set of registered protocols, it has to   re-register with the server. The client can withdraw all registered   services by registering a null set of services. It is important to   note that the server side does not push new information to the   client, neither does the server keep any state describing which   information the client received. It is the responsibility of the   client to update and refresh its information and to discover new   clients or update its stored information about other clients by   issuing queries and registrations at appropriate time intervals. This   simplifies the protocol, but assumes that the client will not store   and request large amounts of data. The main responsibility of the   server is to flood the registered information through the PNNI cloud   such that potential clients can discover each other. The Proxy-PAR   server side also provides filtering functions to support VPNs and IP   subnetting. It is assumed that services advertised by Proxy-PAR will   be advertised by a relatively small number of clients and be fairly   stable, so that polling and refreshing intervals can be relatively   long.   The Proxy-PAR extensions rely on appropriate flooding of information   by the PNNI protocol. When the client side registers or re-registers   a new service through Proxy-PAR, it associates an abstract membership   scope with the service. The server side maps this membership scope   into a PNNI routing level that restricts the flooding. This allows   changes of the PNNI routing level without reconfiguration of the   client. In addition, the server can set up the mapping table such   that a client can flood information only to a certain level. Nodes   within the PNNI network take into account the associated scope of the   information when it is flooded.  It is thus possible to exploit the   PNNI routing hierarchy by announcing different protocols on different   levels of the hierarchy, e.g. OSPF could be run inside certain peer   groups, whereas BGP could be run between the set of peer -groups   running OSPF. Such an alignment or mapping of non-ATM protocols to   the PNNI hierarchy can drastically enhance the scalability and   flexibility of Proxy-PAR service. Figure 1 helps visualize such a   scenario. For this topology the following registrations are issued:Droz & Przygienda            Informational                      [Page 3]

RFC 2843                       Proxy-PAR                        May 2000    +-+    | | PNNI peer group    # PPAR capable  @ PNNI capable  * Router    +-+                      switch          switch                   Level 40                   +---------------------------+                   |                           |                   |                           |                   |      @ ---- @ ---- @      |                   |      |             |      |                   +----- | ----------- | -----+                          |             |           Level 60       |             |           +------------- | ---+    +-- | --------------+           |              |    |    |   |               |      R1* ------#-P1------@    |    |   @---------P3-#------- * R3           |              |    |    |   |               |      R2* ------#-P2------+    |    |   +---------P4-#------- * R4           |                   |    |                   |           +-------------------+    +-------------------+       Figure 1: OSPF and BGP scalability with Proxy-PAR autodetection                               (ATM topology).      1. R1 registers OSPF protocol as running on the IP interface         1.1.1.1 and subnet 1.1.1/24 with scope 60      2. R2 registers OSPF protocol as running on the IP interface         1.1.1.2 and subnet 1.1.1/24 with scope 60      3. R3 registers OSPF protocol as running on the IP interface         1.1.2.1 and subnet 1.1.2/24 with scope 60      4. R4 registers OSPF protocol as running on the IP interface         1.1.2.2 and subnet 1.1.2/24 with scope 60   and      1. R1 registers BGP4 protocol as running on the IP interface         1.1.3.1 and subnet 1.1/16 with scope 40 within AS101      2. R3 registers BGP4 protocol as running on the IP interface         1.1.3.2 and subnet 1.1/16 with scope 40 within AS100Droz & Przygienda            Informational                      [Page 4]

RFC 2843                       Proxy-PAR                        May 2000   For simplicity the real PNNI routing level have been specified, which   are 60 and 40. Instead of these two values the clients would use an   abstract membership scope "local" and "local+1". In addition, all   registered information would be part of the same VPN ID.   Table 1 describes the resulting distribution and visibility of   registrations and whether the routers not only see but also utilize   the received information. After convergence of protocols and the   building of necessary adjacencies and sessions, the overlying IP   topology is illustrated in Figure 2.                     AS101         DMZ      AS100                   #########                ##########                           #                #               |           #   |            #            |               +-- R1 ---------+            #       R4 --+               |           #   |            #            |               |           #   | BGP4 on    #    OSPF on |               | OSPF on   #   | subnet     #     subnet |               | subnet    #   | 1.1/16     #   1.1.2/24 |               | 1.1.1/24  #   |            #            |               |           #   +------------------- R3 --+               +-- R2      #   |            #            |               |           #                #                   #########                ##########       Figure 2: OSPF and BGP scalability with Proxy-PAR autodetection                                (IP topology).   Expressing the above statements differently, one can say that if the   scope of the Proxy-PAR information indicates that a distribution   beyond the boundaries of the peer group is necessary, the leader of a   peer group collects such information and propagates it into a higher   layer of the PNNI hierarchy. As no assumptions except scope values   can normally be made about the information distributed (e.g. IP   addresses bound to AESAs are not assumed to be aligned with them in   any respect), such information cannot be summarized. This makes a   careful handling of scopes necessary to preserve the scalability of   the approach as described above.Droz & Przygienda            Informational                      [Page 5]

RFC 2843                       Proxy-PAR                        May 2000                       Reg#   1. 2. 3. 4. 5. 6.                      Router#                    -----------------------------                      R1      R  U        R  U                      R2      U  R        Q  Q                      R3            R  U  R  U                      R4            U  R  Q  Q                        R registered                        Q seen through query                        U used (implies Q)        Table 1: Flooding scopes of Proxy-PAR registrations.3 Proxy-PAR Protocols3.1 Hello Protocol   The Proxy-PAR Hello Protocol is closely related to the Hello protocol   specified in [2]. It uses the same packet header and version   negotiation methods. For the sake of simplicity, states that are   irrelevant to Proxy-PAR have been removed from the original PNNI   Hello protocol. The purpose of the Proxy-PAR Hello protocol is to   establish and maintain a Proxy-PAR adjacency between the client and   server that supports the exchange of registration and query messages.   If the protocol is executed across multiple, parallel links between   the same server and client pair, individual registration and query   sessions are associated with a specific link. It is the   responsibility of the client and server to assign registration and   query sessions to the various communication instances. Proxy-PAR can   be run in the same granularity as ILMI [4] to support virtual links   and VP tunnels.   In addition to the PNNI Hello, the Proxy-PAR Hellos travelling from   the server to the client inform the client about the lifetime the   server assigns to registered information. The client has to retrieve   this interval from the Hello packet and set its refresh interval to a   value below the obtained time interval in order to avoid the aging   out of registered information by the server.3.2 Registration/Query Protocol   The registration and query protocols enable the client to announce   and learn about protocols supported by the clients. All   query/register operations are initiated by the clients. The server   never tries to push information to the client. It is the client's   responsibility to register and refresh the set of protocols supportedDroz & Przygienda            Informational                      [Page 6]

RFC 2843                       Proxy-PAR                        May 2000   and to re-register them when changes occur. In the same sense, the   client must query the information from the server at appropriate time   intervals if it wishes to obtain the latest information. It is   important to note that neither client nor server is supposed to cache   any state information about the information stored by the other side.   Registered information is associated with an ATM address and scope   inside the PNNI hierarchy. From the IP point of view, all information   is associated with a VPN ID, IP address, subnet mask, and IP protocol   family. In this context, each VPN refers to a completely separated IP   address space. For example <A, 194.194.1.01, 255.255.255.0, OSPF>   describes an OSPF interface in VPN A. In addition to the IP scope   further parameters can be registered that contain more detailed   information about the protocol itself. In the above example this   would be OSPF-specific information such as the area ID or router   priority.  However, Proxy-PAR server takes only the ATM and IP-   specific information into account when retrieving information that   was queried. Protocol specific information is never looked at by a   Proxy-PAR server.3.2.1 Registration Protocol   The registration protocol enables a client to register the protocols   and services it supports. All protocols are associated with a   specific AESA and membership scope in the PNNI hierarchy.  As the   default scope, implementations should choose the local scope of the   PNNI peer group. In this way, manual configuration can be avoided   unless information has to cross PNNI peer group boundaries. PNNI is   responsible for the correct flooding either in the local peer group   or across the hierarchy.   The registration protocol is aligned with the standard initial   topology database exchange protocol used in link-state routing   protocols as far as possible. It uses a window size of one. A single   information element is registered at a time and must be acknowledged   before a new registration packet can be sent. The protocol uses '   initialization' and 'more' bits in the same manner PNNI and OSPF do.   Any registration on a link unconditionally overwrites all   registration data previously received on the same link. By means of a   return code the server indicates to the client whether the   registration was successful.   Apart form the IP-related information, the protocol also offers a   generic interface to the PNNI flooding. By means of so-called System   Capabilities Information Groups other information can be distributed   that can be used for proprietary or experimental implementations.Droz & Przygienda            Informational                      [Page 7]

RFC 2843                       Proxy-PAR                        May 20003.2.2 Query Protocol   The client uses the query protocol to obtain information about   services registered by other clients. The client requests services   registered within a specific membership scope, VPN and IP address   prefix. It is always the client's task to request information, the   server never makes an attempt to push information to the client. If   the client needs to filter the returned data based on service-   specific information, such as BGP AS, it must parse and interpret the   received information. The server never looks beyond the IP scope.   The more generic interface to the flooding is supported in a similar   manner as the registration protocol.4 Supported Protocols   Currently the protocols indicated in Table 2 have been included.   Furthermore, for protocols marked 'yes', additional information has   been specified that is beneficial for their operation. Many of the   protocols do not need additional information; it is sufficient to   know they are supported and to which addresses they are bound.   To include other information in an experimental manner the generic   information element can be used to carry such information.5 VPN Support   To implement virtual private networks all information distributed via   PAR can be scoped under a VPN ID [1]. Based on this ID, individual   VPNs can be separated. Inside a certain VPN further distinctions can   be made according to IP-address-related information and/or protocol   type.   In most cases the best VPN support can be provided when Proxy-PAR is   used between the client and server because in this way it is possible   to hide the real PNNI topology from the client. The PAR capable   server translates from the abstract membership scope into the real   PNNI routing level. In this way the real PNNI topology is hidden from   the client and the server can apply restrictions in the PNNI scope.   The server can for instance have a mapping such that the membership   scope "global" is mapped to the highest level peer group to which a   particular VPN has access. Thus the membership scopes can be seen as   hierarchical structuring inside a certain VPN. With such mappings a   network provider can also change the mapping without having to   reconfigure the clients.Droz & Przygienda            Informational                      [Page 8]

RFC 2843                       Proxy-PAR                        May 2000   For more secure VPN implementations it will also be necessary to   implement VPN ID filters on the server side. In this way a client can   be restricted to a certain set (typically one) of VPN IDs.  The   server will then allow queries and registrations only from the   clients that are in the allowed VPNs. In this way it is possible to   avoid an attached client from finding devices that are outside of its   own VPN.  There is even room for further restriction in terms of not   allowing wildcard queries by a client. In terms of security, some of   the protocols have their own methods, so PAR is only used for the   discovery of the counterparts. For instance OSPF has an   authentication that can be used during the OSPF operation. Hence even   in the case where two wrong partners find each other, they will not   communicate because they will not be able to authenticate each other.                       Protocol    Additional Info                     -------------------------------                       OSPF              yes                       RIP                       RIPv2                       BGP3                       BGP4              yes                       EGP                       IDPR                       MOSPF             yes                       DVMRP                       CBT                       PIM-SM                       IGRP                       IS-IS                       ES-IS                       ICMP                       GGP                       BBN SPF IGP                       PIM-DM                       MARS                       NHRP                       ATMARP                       DHCP                       DNS               yes   Table 2: Additional protocol information carried in PAR and PPAR.   The VPN ID used by PAR and Proxy-PAR is aligned with the VPN ID used   by other protocols from the ATM Forum and IETF. The VPN ID is   structured into two parts, namely the 3-byte-long OUI plus a 4-byte   index.Droz & Przygienda            Informational                      [Page 9]

RFC 2843                       Proxy-PAR                        May 20006 Interoperation with ILMI based Server Discovery   PAR can be used to complement the server discovery via ILMI as   specified in [11,12,13]. It can be used to provide the flooding of   information across the PNNI network. For this purpose a server has to   register with a PAR-capable device.  This can be achieved via Proxy-   PAR or a direct PAR interaction.  Manual configuration would also be   possible. For instance the ATMARP server could register its service   via Proxy-PAR. A direct interaction with PAR will be required in   order to provide an appropriate flooding scope.   A PAR-capable device that has the additional MIB variables in the   Service Registry MIB can set these variables when getting information   via PAR. All required information is either contained in PAR or is   static, such as the IP version.7 Security Consideration   The Proxy-PAR protocol itself does not have its own security   concepts.  As PAR is an extension of PNNI, it has all the security   features that come with PNNI. In addition, the protocol is mainly   used for automatic discovery of peers for certain protocols.  After   the discovery process the security concepts of the individual   protocol are used for the bring-up. As explained in the section about   VPN support, the only security considerations are on the server side,   where access filters for VPN IDs can be implemented and restrictive   membership scope mappings can be configured.8 Conclusion   This document describes the basic functions of Proxy-PAR, which has   been specified within the ATM Forum body. The main purpose of the   protocol is to provide automatic detection and configuration of non-   ATM devices over an ATM cloud.   In the future, support for further protocols and address families may   be added to widen the scope of applicability of Proxy-PAR.Droz & Przygienda            Informational                     [Page 10]

RFC 2843                       Proxy-PAR                        May 20009 Bibliography   [1]  Fox, B. and B. Gleeson, "Virtual Private Networks Identifier",RFC 2685, September 1999.   [2]  ATM-Forum, "Private Network-Network Interface Specification        Version 1.0." ATM Forum af-pnni-0055.000, March 1996.   [3]  ATM-Forum, "PNNI Augmented Routing (PAR) Version 1.0."  ATM        Forum af-ra-0104.000, January 1999.   [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]  Moy, J., "Extending OSPF to Support Demand Circuits",RFC 1793,        April 1995.   [7]  ATM-Forum, "LAN Emulation over ATM 1.0." ATM Forum af-lane-        0021.000, January 1995.   [8]  Armitage, G., "Support for Multicast over UNI 3.0/3.1 based ATM        Networks",RFC 2022, November 1996.   [9]  Droz, P., Haas, R. and T. Przygienda, "OSPF over ATM and Proxy        PAR",RFC 2844, May 2000.   [10] Coltun, R., "The OSPF Opaque LSA Option",RFC 2328, July 1998.   [11] Davison, M., "ILMI-Based Server Discovery for ATMARP",RFC 2601,        June 1999.   [12] Davison, M., "ILMI-Based Server Discovery for MARS",RFC 2602,        June 1999.   [13] Davison, M., "ILMI-Based Server Discovery for NHRP",RFC 2603,        June 1999.Droz & Przygienda            Informational                     [Page 11]

RFC 2843                       Proxy-PAR                        May 2000Authors' Addresses   Patrick Droz   IBM Research   Zurich Research Laboratory   Saumerstrasse 4   8803 Ruschlikon   Switzerland   EMail: dro@zurich.ibm.com   Tony Przygienda   Siara Systems Incorporated   1195 Borregas Avenue   Sunnyvale, CA 94089   USA   EMail: prz@siara.comDroz & Przygienda            Informational                     [Page 12]

RFC 2843                       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.Droz & Przygienda            Informational                     [Page 13]