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Network Working Group P. Droz Request for Comments: 2843 IBM Category: Informational T. Przygienda

                                                             May 2000

Status 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.


 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

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
 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 of RFC2225 [5], or use RFC1793 [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 sending

Droz & 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
 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 and subnet 1.1.1/24 with scope 60
    2. R2 registers OSPF protocol as running on the IP interface and subnet 1.1.1/24 with scope 60
    3. R3 registers OSPF protocol as running on the IP interface and subnet 1.1.2/24 with scope 60
    4. R4 registers OSPF protocol as running on the IP interface and subnet 1.1.2/24 with scope 60
    1. R1 registers BGP4 protocol as running on the IP interface and subnet 1.1/16 with scope 40 within AS101
    2. R3 registers BGP4 protocol as running on the IP interface and subnet 1.1/16 with scope 40 within AS100

Droz & 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.
                    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 Protocols

3.1 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 supported

Droz & 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,,, 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 2000

3.2.2 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
 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
  1. ——————————

OSPF yes

                     BGP4              yes
                     MOSPF             yes
                     BBN SPF IGP
                     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

Droz & Przygienda Informational [Page 9] RFC 2843 Proxy-PAR May 2000

6 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 2000

9 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
 [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 2000

Authors' Addresses

 Patrick Droz
 IBM Research
 Zurich Research Laboratory
 Saumerstrasse 4
 8803 Ruschlikon
 Tony Przygienda
 Siara Systems Incorporated
 1195 Borregas Avenue
 Sunnyvale, CA 94089

Droz & Przygienda Informational [Page 12] RFC 2843 Proxy-PAR May 2000

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Droz & Przygienda Informational [Page 13]

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