Network Working Group                                   M. Rose, Editor
Request for Comments: 1161      Performance Systems International, Inc.
                                                              June 1990


                             SNMP over OSI

Table of Contents

   1. Status of this Memo ...................................    1
   2. Background ............................................    1
   2.1 A Digression on User Interfaces ......................    2
   2.1.1 Addressing Conventions for UDP-based service .......    3
   2.2 A Digression of Layering .............................    3
   3. Mapping onto CLTS .....................................    4
   3.1 Addressing Conventions ...............................    4
   3.1.1 Conventions for CLNP-based service .................    4
   4. Mapping onto COTS .....................................    4
   4.1 Addressing Conventions ...............................    5
   4.1.1 Conventions for TP4/CLNP-based service .............    5
   4.1.2 Conventions for TP0/X.25-based service .............    6
   5. Acknowledgements ......................................    6
   6. References ............................................    7
   7. Security Considerations................................    8
   8. Author's Address.......................................    8

1.  Status of this Memo

   This memo defines an experimental means for running the Simple
   Network Management Protocol (SNMP) over OSI transports.

   This memo does not specify a standard for the Internet community,
   However, after experimentation, if sufficient consensus is reached in
   the Internet community, then a subsequent revision of this document
   might be made an Internet standard for those systems choosing to
   implement the SNMP over OSI transport services.

   Distribution of this memo is unlimited.

2.  Background

   The Simple Network Management Protocol (SNMP) as defined in [1] is
   now used as an integral part of the network management framework for
   TCP/IP-based internets.  Together, with its companions standards,
   which define the Structure of Management Information (SMI) [2], and
   the Management Information Base (MIB) [3], the SNMP has received
   widespread deployment in many operational networks running the
   Internet suite of protocols.

   It should not be surprising that many of these sites might acquire
   OSI capabilities and may wish to leverage their investment in SNMP
   technology towards managing those OSI components.  This memo
   addresses these concerns by defining a framework for running the SNMP
   in an environment which supports the OSI transport services.

   In OSI, there are two such services, a connection-oriented transport
   services (COTS) as defined in [4], and a connectionless-mode
   transport service (CLTS) as defined in [5].  Although the primary
   deployment of the SNMP is over the connectionless-mode transport
   service provided by the Internet suite of protocols (i.e., the User
   Datagram Protocol or UDP [6]), a design goal of the SNMP was to be
   able to use either a CO-mode or CL-mode transport service.  As such,
   this memo describes mappings from the SNMP onto both the COTS and the
   CLTS.

2.1.  A Digression on User Interfaces

   It is likely that user-interfaces to the SNMP will be developed that
   support multiple transport backings.  In an environment such as this,
   it is often important to maintain a consistent addressing scheme for
   users.  Since the mappings described in this memo are onto the OSI
   transport services, use of the textual scheme described in [7], which
   describes a string encoding for OSI presentation addresses, is
   recommended.  The syntax defined in [7] is equally applicable towards
   transport addresses.

   In this context, a string encoding usually appears as:

      [<t-selector>/]<n-provider><n-address>[+<n-info>]

      where:

      (1)  <t-selector> is usually either an ASCII string enclosed
           in double-quotes (e.g., "snmp"), or a hexadecimal number
           (e.g., '736e6d70'H);

      (2)  <n-provider> is one of several well-known providers of a
           connectivity-service, one of: "Internet=" for a
           transport-service from the Internet suite of protocols,
           "Int-X25=" for the 1980 CCITT X.25 recommendation, or
           "NS+" for the OSI network service;

      (3)  <n-address> is an address in a format specific to the
           <n-provider>; and,

      (4)  <n-info> is any additional addressing information in a
           format specific to the <n-provider>.

   It is not the purpose of this memo to provide an exhaustive
   description of string encodings such as these.  Readers should
   consult [7] for detailed information on the syntax.  However, this
   memo recommends that, as an implementation option, user-interfaces to
   the SNMP that support multiple transport backings SHOULD implement
   this syntax.

2.1.1.  Addressing Conventions for UDP-based service

   In the context of a UDP-based transport backing, addresses would be
   encoded as:

                           Internet=<host>+161+2

   which says that the transport service is from the Internet suite of
   protocols, residing at <host>, on port 161, using the UDP (2).  The
   token <host> may be either a domain name or a dotted-quad, e.g., both

                     Internet=cheetah.nyser.net+161+2

   and

                        Internet=192.52.180.1+161+2

   are both valid.  Note however that if domain name "cheetah.nyser.net"
   maps to multiple IP addresses, then this implies multiple transport
   addresses.  The number of addresses examined by the application (and
   the order of examination) are specific to each application.

   Of course, this memo does not require that other interface schemes
   not be used.  Clearly, use of a simple hostname is preferable to the
   string encoding above.  However, for the sake of uniformity, for
   those user-interfaces to the SNMP that support multiple transport
   backings, it is strongly RECOMMENDED that the syntax in [7] be
   adopted and even the mapping for UDP-based transport be valid.

2.2.  A Digression of Layering

   Although other frameworks view network management as an application,
   extensive experience with the SNMP suggests otherwise.  In essense,
   network management is a function unlike any other user of a transport
   service.  The citation [8] develops this argument in full.  As such,
   it is inappropriate to map the SNMP onto the OSI application layer.
   Rather, it is mapped to OSI transport services, in order to build on
   the proven success of the Internet network management framework.

3.  Mapping onto CLTS

   Mapping the SNMP onto the CLTS is straight-forward: the elements of
   procedure are identical to that of using the UDP.  In particular,
   note that the CLTS and the service offered by the UDP both transmit
   packets of information which contain full addressing information.
   Thus, mapping the SNMP onto the CLTS, a "transport address" in the
   context of [1], is simply a transport-selector and network address.

3.1.  Addressing Conventions

   Unlike the Internet suite of protocols, OSI does not use well-known
   ports.  Rather demultiplexing occurs on the basis of "selectors",
   which are opaque strings of octets, which have meaning only at the
   destination.  In order to foster interoperable implementations of the
   SNMP over the CLTS, it is necessary define a selector for this
   purpose.

3.1.1.  Conventions for CLNP-based service

   When the CLTS is used to provide the transport backing for the SNMP,
   demultiplexing will occur on the basis of transport selector.  The
   transport selector used shall be the four ASCII characters

                                   snmp

   Thus, using the string encoding of [7], such addresses may be
   textual, described as:

                             "snmp"/NS+<nsap>

   where:

   (1)  <nsap> is a hex string defining the nsap, e.g.,

                     "snmp"/NS+4900590800200038bafe00

   Similarly, SNMP traps are, by convention, sent to a manager listening
   on the transport selector

                                 snmp-trap

   which consists of nine ASCII characters.

4.  Mapping onto COTS

   Mapping the SNMP onto the COTS is more difficult as the SNMP does not
   specifically require an existing connection.  Thus, the mapping

   consists of establishing a transport connection, sending one or more
   SNMP messages on that connection, and then releasing the transport
   connection.

   Consistent with the SNMP model, the initiator of a connection should
   not require that responses to a request be returned on that
   connection.  However, if a responder to a connection sends SNMP
   messages on a connection, then these MUST be in response to requests
   received on that connection.

   Ideally, the transport connection SHOULD be released by the
   initiator, however, note that the responder may release the
   connection due to resource limitations.  Further note, that the
   amount of time a connection remains established is implementation-
   specific.  Implementors should take care to choose an appropriate
   dynamic algorithm.

   Also consistent with the SNMP model, the initiator should not
   associate any reliability characteristics with the use of a
   connection.  Issues such as retransmission of SNMP messages, etc.,
   always remain with the SNMP application, not with the transport
   service.

4.1.  Addressing Conventions

   Unlike the Internet suite of protocols, OSI does not use well-known
   ports.  Rather demultiplexing occurs on the basis of "selectors",
   which are opaque strings of octets, which have meaning only at the
   destination.  In order to foster interoperable implementations of the
   SNMP over the COTS, it is necessary define a selector for this
   purpose.  However, to be consistent with the various connectivity-
   services, different conventions, based on the actual underlying
   service, will be used.

4.1.1.  Conventions for TP4/CLNP-based service

   When a COTS based on the TP4/CLNP is used to provide the transport
   backing for the SNMP, demultiplexing will occur on the basis of
   transport selector.  The transport selector used shall be the four
   ASCII characters

                                   snmp

   Thus, using the string encoding of [7], such addresses may be
   textual, described as:

                             "snmp"/NS+<nsap>

   where:

   (1)  <nsap> is a hex string defining the nsap, e.g.,

                     "snmp"/NS+4900590800200038bafe00

   Similarly, SNMP traps are, by convention, sent to a manager listening
   on the transport selector

                                 snmp-trap

   which consists of nine ASCII characters.

4.1.2.  Conventions for TP0/X.25-based service

   When a COTS based on the TP0/X.25 is used to provide the transport
   backing for the SNMP, demultiplexing will occur on the basis of X.25
   protocol-ID.  The protocol-ID used shall be the four octets

                                 03018200

   Thus, using the string encoding of [7], such addresses may be textual
   described as:

                        Int-X25=<dte>+PID+03018200

   where:

   (1)  <dte> is the X.121 DTE, e.g.,

                    Int-X25=23421920030013+PID+03018200

   Similarly, SNMP traps are, by convention, sent to a manager listening
   on the protocol-ID

                                 03019000

5.  Acknowledgements

   This document was produced by the SNMP Working Group:

         Karl Auerbach, Epilogue Technology
         David Bridgham, Epilogue Technology
         Brian Brown, Synoptics
         John Burress, Wellfleet
         Jeffrey D. Case, University of Tennessee at Knoxville
         James R. Davin, MIT-LCS
         Mark S. Fedor, PSI, Inc.

         Stan Froyd, ACC
         Satish Joshi, Synoptics
         Ken Key, University of Tennessee at Knoxville
         Gary Malkin, FTP Software
         Randy Mayhew, University of Tennessee at Knoxville
         Keith McCloghrie, Hughes LAN Systems
         Marshall T. Rose, PSI, Inc. (chair)
         Greg Satz, cisco
         Martin Lee Schoffstall, PSI, Inc.
         Bob Stewart, Xyplex
         Geoff Thompson, Synoptics
         Bill Versteeg, Network Research Corporation
         Wengyik Yeong, PSI, Inc.

6.  References

  [1]  Case, J., Fedor, M., Schoffstall, M., and J. Davin, "A Simple
       Network Management Protocol (SNMP)", RFC 1157, SNMP Research,
       Performance Systems International, Performance Systems
       International, and MIT Laboratory for Computer Science, May 1990.

  [2]  Rose M., and K. McCloghrie, "Structure and Identification of
       Management Information for TCP/IP-based internets", RFC 1155,
       Performance Systems International, Hughes LAN Systems, May 1990.

  [3]  McCloghrie K., and M. Rose, "Management Information Base for
       Network Management of TCP/IP-based internets", RFC 1156, Hughes
       LAN Systems, Performance Systems International, May 1990.

  [4]  Information Processing Systems - Open Systems Interconnection,
       "Transport Service Definition", International Organization for
       Standardization, International Standard 8072, June 1986.

  [5]  Information Processing Systems - Open Systems Interconnection,
       "Transport Service Definition - Addendum 1: Connectionless-mode
       Transmission", International Organization for Standardization,
       International Standard 8072/AD 1, December 1986.

  [6]  Postel, J., "User Datagram Protocol", RFC 768, USC/Information
       Sciences Institute, November 1980.

  [7]  Kille, S., "A String Encoding of Presentation Address", Research
       Note RN/89/14, Department of Computer Science, University College
       London, February 1989.

  [8]  Case, J., Davin, J., Fedor, M., and M. Schoffstall, "Network
       Management and the Design of SNMP", ConneXions (ISSN 0894-5926),
       Volume 3, Number 3, March 1989.

7.  Security Considerations

   Security issues are not discussed in this memo.

8.  Author's Address

   Marshall T. Rose
   PSI, Inc.
   PSI California Office
   P.O. Box 391776
   Mountain View, CA 94039

   Phone: (415) 961-3380

   Email: mrose@PSI.COM