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  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) , and the Management Information Base (MIB) , 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 , and a connectionless-mode transport service (CLTS) as defined in . 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 ), 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 , which describes a string encoding for OSI presentation addresses, is recommended. The syntax defined in  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  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=184.108.40.206+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  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  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 , 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 , 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 , 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 , 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  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.  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.  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.  Information Processing Systems - Open Systems Interconnection, "Transport Service Definition", International Organization for Standardization, International Standard 8072, June 1986.  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.  Postel, J., "User Datagram Protocol", RFC 768, USC/Information Sciences Institute, November 1980.  Kille, S., "A String Encoding of Presentation Address", Research Note RN/89/14, Department of Computer Science, University College London, February 1989.  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.