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Author Patrick Droz 
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Internet Engineering Task Force                    P. Droz/T. Przygienda
INTERNET DRAFT                               IBM Corp./Bell Labs, Lucent
                                                        15 February 1999

                               Proxy PAR

Status of This Memo
   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Internet Drafts are working
   documents of the Internet Engineering Task Force (IETF), its Areas,
   and its Working Groups.  Note that other groups may also distribute
   working documents as Internet Drafts.

   Internet Drafts are draft documents valid for a maximum of six
   months.  Internet Drafts may be updated, replaced, or obsoleted by
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   Drafts as reference material, or to cite them other than as a
   ``working draft'' or ``work in progress.''
   Please check the I-D abstract listing contained in each Internet
   Draft directory to learn the current status of this or any other
   Internet Draft.

   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 where 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 addresses mainly protocols available in IPv4.  But
   it also disposes of a generic interface to access the flooding of
   PNNI. In addition, Proxy PAR capable servers provide filtering based
   on VPN IDs, 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.

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1. Introduction

   In June 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 PNNI working
   group [AF96b].  The PAR [Ca96] specification provides a detailed
   description of the protocol including state machines and packet
   The intention of this I-D is to provide general information about
   Proxy PAR. For the detailed protocol description we refer the reader
   to [Ca96].

   Proxy PAR is a protocol allowing for different 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 device such as IP routers.  Additionally, clients can use Proxy
   PAR to register different non-ATM services and protocols they
   support.  The protocol has deliberately not been included as part of
   ILMI [AF96a] 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 executing Proxy PAR does not
   necessarily need to execute ILMI or UNI signalling although this
   normally will 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 of RFC1577 [Lau94], or use RFC1793 [Moy95]
   to interact with each other.  For the same purpose LANE [AF95] or
   MARS [Arm96] could be used.  It is expected that the guidelines how
   a certain protocol can make use of Proxy PAR should come out of the
   appropriate working group or standardization body that is responsible
   for the particular protocol.  Currently, work in progress exists
   to address the operation of OSPF in the context of ATM and Proxy
   PAR [DP97].  Further work will address other protocols such as BGP-4.

   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. [CH97, Col97].
   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

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   not least, it should be mentioned here as well that the protocol
   complements and coexists with the ongoing work in the IETF on server
   detection via ILMI extensions [Dav97a, Dav97b, Dav97c].

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
   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 it's 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 will
   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 membeship
   scope with the service.  The server side maps this membership scope
   into a PNNI routing level that restricts the flooding.  This allows
   the changes of the PNNI routing level without reconfiguration of the
   client.  In addition, the server can setup the mapping table such
   that a client can only flood information 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

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 | | 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

   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 increase the scalability and
   flexibility of Proxy PAR service.  Figure 1 helps to visualize such a
   scenario.  For this topology following registrations are issued:

    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

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    4. R4 registers OSPF protocol as running on the IP interface
       and subnet 1.1.2/24 with scope 60

    5. R1 registers BGP4 protocol as running on the IP interface
       and subnet 1.1/16 with scope 40 within AS101

    6. R3 registers BGP4 protocol as running on the IP interface
       and subnet 1.1/16 with scope 40 within AS100

   For simplicity the real PNNI routing level have been specified which
   are 60 and 40.  Instead of these two values the clients would use as
   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
   building of necessary adjacencies and sessions the overlying IP
   topology is visualized in Figure 2.

   Expressing the said above 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

          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

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           Reg# |1. |2. |3. |4. |5. |6.
     ___Router#_|___|___|___|___|___|____   R  registered
        R1      |R  |U  |   |   |R  |U      Q  seen through query
        R2      |U  |R  |   |   |Q  |Q      U  used (implies Q)
        R3      |   |   |R  |U  |R  |U
        R4      |   |   |U  |R  |Q  |Q

          Table 1:  Flooding Scopes of Proxy PAR Registrations

   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 summarised.  This makes a
   careful handling of scopes necessary to preserve the scalability of
   the approach as described above.

3. Proxy PAR Protocols

3.1. The Hello Protocol
   The Proxy PAR Hello Protocol is closely related to the Hello protocol
   specified in [AF96b].  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
   bring up 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 different communication instances.  Proxy PAR
   can be run in the same granularity as ILMI [AF96a] 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.

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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
   and 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 only takes
   the ATM and IP specific information into account when retrieving
   information that was queried for.  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 peergroup 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

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   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 or not.

   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.

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 any 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 similar to
   the registration protocol.

4. Supported Protocols
   Currently the protocols indicated in Table 2 have been included.
   Furthermore, for protocols marked with a 'yes' additional information
   has been specified that is beneficial for their operation.  Many of
   the protocol do not need additional information, it is sufficient to
   know that they are supported and to know to which addresses they are

   In order to include other information in an experimental manner the
   generic information element can be used to carry such information.

5. VPN Support

   In order to implement virtual private networks all information
   distributed via PAR can be scoped under a VPN ID. 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

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                       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

   server performs the translation 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
   peergroup 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
   having to reconfigure the clients.
   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

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   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 security methods, so PAR is only
   used for the discovery of the counterparts.  For instance OSPF has
   authentication which can be used during the OSPF operation.  So 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.

   The VPN ID used by PAR and Proxy PAR is aligned with the VPN ID used
   by other protocols from the ATM Forum.  The VPN ID is structured into
   2 parts, namely the 3 bytes long OUI plus a 4 byte index.

6. Interoperation with ILMI based Server Discovery

   PAR can be used to complement the server discovery via ILMI as
   specified in [Dav97a, Dav97b, Dav97c].  It can be used to provide
   the flooding of the 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 with 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
   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 IP version.  The ATM Forum is specifying the
   mapping of the PAR information into the Service Registry MIB. This
   specification will be pubished as an Appendix to the PAR document.

7. Security Consideration
   The Proxy PAR protocol itself does not have its own security
   concepts.  As PAR is an extension to PNNI, it has all 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 is used for the bring up.  As explained in the section about
   VPN support, the only security considerations are on the server side

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   where access filters for VPN IDs can be implemented and restrictive
   membership scope mappings can be configured.

8. Conclusion
   This I-D describes the basic functions of Proxy PAR that 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.


   [AF95]   ATM-Forum.  LAN Emulation over ATM 1.0.  ATM Forum
            af-lane-0021.000, January 1995.

   [AF96a]  ATM-Forum.  Interim Local Management Interface (ILMI)
            Specification 4.0.  ATM Forum 95-0417R8, June 1996.

   [AF96b]  ATM-Forum.  Private Network-Network Interface Specification
            Version 1.0.  ATM Forum af-pnni-0055.000, March 1996.

   [Arm96]  G. Armitage.  Support for Multicast over UNI 3.0/3.1 based
            ATM Networks, RFC 2022.  Internet Engineering Task Force,
            November 1996.

   [Ca96]   R. Callon and al.  An Overview of PNNI Augmented Routing.
            ATM Forum 96-0354, April 1996.

   [CH97]   R. Coltun and J. Heinanen.  The OSPF Address Resolution
            Advertisement Option.  Internet Draft, 1997.

   [Col97]  R. Coltun.  Opaque LSA in OSPF.  Internet Draft, 1997.

   [Dav99a] M. Davison.  ILMI-Based Server Discovery for ATMARP.
            Internet Draft, 1999.

   [Dav99b] M. Davison.  ILMI-Based Server Discovery for MARS.  Internet
            Draft, 1999.

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   [Dav99c] M. Davison.  ILMI-Based Server Discovery for NHRP.  Internet
            Draft, 1999.

   [DP97]   P. Droz and T. Przygienda.  OSPF over ATM and Proxy PAR.
            Internet Draft, 1997.

   [Lau94]  M. Laubach.  Classical IP and ARP over ATM, RFC 1577.
            Internet Engineering Task Force, January 1994.

   [Moy95]  J. Moy.  Extending OSPF to Support Demand Circuits, RFC
            1793.  Internet Engineering Task Force, April 1995.

Authors' Addresses

Tony Przygienda
Bell Labs, Lucent Technologies
101 Crawfords Corner Road
Holmdel, NJ 07733-3030

Patrick Droz
IBM Research Division
Zurich Research Laboratory
Saumerstrasse 4
8803 Ruschlikon

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