Network Working Group                                       M. Davison
Request for Comments: 2603                               Cisco Systems
Category:  Standards Track                                   June 1999

                  ILMI-Based Server Discovery for NHRP

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.


   This memo defines how ILMI-based Server Discovery, which provides a
   method for ATM-attached hosts and routers to dynamically determine
   the ATM addresses of servers, shall be used to locate NHRP servers.

1. Introduction

   Presently, configuring a host or router to use NHRP [1] is cumbersome
   and error-prone since it requires at least one ATM address to be
   statically configured on each host or router in the network.
   Further, it is impossible to implement a diskless host to use NHRP
   since local configuration is required.  ILMI-based Server Discovery,
   hereafter referred to as "server discovery," provides a solution to
   these problems.

   A brief overview of the Integrated Local Management Interface (ILMI)
   and the Service Registry MIB, as defined by the ATM Forum, are
   provided in this memo. The reader should consult [2] for a complete
   description of ILMI and this MIB, but the information contained here
   is sufficient for an understanding of its use to support NHRP server

2. Integrated Local Management Interface

   The Integrated Local Management Interface (ILMI) [2] provides a
   mechanism for ATM-attached devices, such as hosts, routers, and ATM
   switches, to transfer management information. It is based on the
   Simple Network Management Protocol (SNMP), Version 1, and supports

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   get, get-next, set and trap operations.

   The ILMI specification designates the switch side of the ATM link as
   the 'network side' and the host/router side of the ATM link as the '
   user side.' The Service Registry MIB, which is outlined in Section 3,
   is implmented on the network side and is queried from the user side.

3. ILMI 4.0 Service Registry MIB

   Server discovery utilizes the Service Registry MIB defined by the ATM
   Forum in ILMI Specification Version 4.0 [2]. To support the existing
   framework for IP over ATM, ATM switches must support the Service
   Registry MIB.

   A row in the service registry table [2] is defined as:

      AtmfSrvcRegEntry ::= SEQUENCE {
          atmfSrvcRegPort          INTEGER,
          atmfSrvcRegServiceID     OBJECT IDENTIFIER,
          atmfSrvcRegATMAddress    AtmAddress,
          atmfSrvcRegAddressIndex  INTEGER,
          atmfSrvcRegParm1         OCTET STRING

   The definition of each field in this structure is:

      atmfSrvcRegPort - The ATM port number for which this entry
          contains management information. The value of zero may be used
          to indicate the ATM interface over which a management request
          was received.

      atmfSrvcRegServiceID - This is the service identifier that
          uniquely identifies the type of service at the address
          provided in the table. (See Section 3.2 for NHRP OID.)

      atmfSrvcRegATMAddress - This is the full address of the service.
          The ATM client will use this address to establish a connection
          with the service.

      atmfSrvcRegAddressIndex - An arbitrary integer to differentiate
          multiple rows containing different ATM addresses for the same
          service on the same port.

      atmfSrvcRegParm1 - An octet string whose size and meaning is
          determined by the value of atmfSrvcRegServiceID.

   The service registry table is indexed by atmfSrvcRegPort,
   atmfSrvcRegServiceID and atmfSrvcRegAddressIndex.

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3.1 Service Parameter String

   A generic parameter string is defined in the service registry table,
   thus allowing protocol-specific parameters to be specified. To be
   consistent with [1], the parameter string for NHRP shall be:

       ar$pro.type   16   bits     Protocol type
       ar$pro.snap   40   bits     Optional extension to protocol type
       ar$plen        8   bits     Length of protocol address
       ar$addr       plen octets   Network address
       ar$mask       plen octets   Network mask


       ar$pro.type   - See [1]. (IPv4 is 0x0800, IPv6 is 0x86DD)

       ar$pro.snap   - See [1]. (IPv4 and IPv6 are 0)

       ar$plen       - Length of the protocol address.
                        (IPv4 is 4, IPv6 is 16)

       ar$addr       - Network address represented in network byte

       ar$mask       - Network mask represented in network byte order

3.2 Service Object Identifier

   This OID, assigned in the ATM Forum Service Registry MIB, names
   ATMARP within the context of server discovery.

     atmfSrvcRegNHRP OBJECT IDENTIFIER ::= { }

      It does not name any managed objects, rather is used to locate
      appropriate rows in the service registery table.

4. Next Hop Client Behavior

   An Next Hop Client NHC) will access the service registry table via
   ILMI using the SNMP GetNext operator to "sweep" (SNMP parlance for a
   linear search) beginning with {Port = 0, ServiceID = <see Section
   3.2>, Index = 0} while holding the port number and the serviceID
   constant. (Port number 0 is used within ILMI to indicate "this

   An NHC with no local configuration, such as a diskless workstation,

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   must use the row with the lowest index value if multiple Next Hop
   Server (NHS), possibly for multiple networks, are listed.

   NHC that have local IP configuration must use a row that has the
   appropriate IP address.  For example, consider the case where an IP
   router has 3 logical interfaces defined on a single physical
   interface with IP addresses, and The router will sweep the service registry table
   looking for rows that have atmfSrvcRegParm1 values as shown below:

     Net number/mask  atmfSrvcRegParm1
     ---------------- --------------------------------------------------        08 00 00 00 00 00 00  04  01 00 00 00  ff 00 00 00    08 00 00 00 00 00 00  04  80 0a 00 00  ff ff 00 00  08 00 00 00 00 00 00  04  ab 45 96 00  ff ff ff 00

   When the correct atmfSrvcRegParm1 values are located, the router may
   then establish an SVC to the selected NHS and perform the appropriate
   protocol operations.

   Redundant NHS are supported with multiple rows in the service
   registry table. This list of NHS is ordered with the primary NHS
   having the lowest index value. The NHC must attempt to utilize the
   primary NHS before utilizing a secondary NHS. Administrators must
   ensure that the listed NHS are synchronized.

5. NHRP Server (NHS) Behavior

   A Next Hop Server (NHS) shall be locally configured. The NHS may
   retrieve the NHRP service registry data to validate the results. If
   an incorrect row is retrieved the error may be flagged in a locally
   significant way.

6. Relationship with PNNI Augmented Routing

   An augmented version PNNI ("PNNI Augmented Routing," or PAR) [3] has
   been developed by the ATM Forum. PAR can distribute data such as NHS
   addresses. Further, the ATM Forum is developing a proxy mechanism for
   PAR (Proxy PAR) that would allow a UNI-attached host or router to
   access PAR data without a full PAR implementation.

   These mechanisms offer a promising way to manage the service registry
   tables maintained on each switch in an ATM network, yet would not
   require changes to the mechanism defined in this memo. Hosts and
   routers can continue to utilize ILMI-based or Proxy PAR-based server
   discovery and network administrators could manage the service
   registry data with local configuration or via PAR and Proxy PAR.

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7. Security Considerations

   The server discovery mechanism is built on the ILMI managment
   framework and the security embodied in that framework. Access, to
   user- or network-side information is controlled by MIB design rather
   than protocol security mechanisms.

   The service registery MIB, the table containing information for
   server discovery, is defined in [2] with read-only access. This means
   that any user-side device may query the service registry, but may not
   modify the service registry via ILMI. Instead, the sevice registry
   table must be modified via local configuration on the ATM switch.


   [1]  Luciani, J., et al., "NBMA Next Hop Resolution Protocol", RFC
        2332, April 1998.

   [2]  ATM Forum, "Integrated Local Management Interface (ILMI)
        Specification Version 4.0," af-ilmi-0065.000, September 1996.

   [3]  ATM Forum, "PNNI Augmented Routing (PAR) Version 1.0," af-ra-
        0104, January 1999.

Author's  Address

   Mike Davison
   Cisco Systems
   170 West Tasman Drive
   San Jose, California 95134

   Phone: (408) 526-4000
   EMail: mike.davison@cisco.com

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RFC 2603          ILMI-Based Server Discovery for NHRP         June 1999

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