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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

Davison Standards Track [Page 1] RFC 2603 ILMI-Based Server Discovery for NHRP June 1999

 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.

Davison Standards Track [Page 2] RFC 2603 ILMI-Based Server Discovery for NHRP June 1999

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,

Davison Standards Track [Page 3] RFC 2603 ILMI-Based Server Discovery for NHRP June 1999

 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.

Davison Standards Track [Page 4] RFC 2603 ILMI-Based Server Discovery for NHRP June 1999

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

Davison Standards Track [Page 5] RFC 2603 ILMI-Based Server Discovery for NHRP June 1999

Full Copyright Statement

 Copyright (C) The Internet Society (1999).  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
 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


 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Davison Standards Track [Page 6]

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