Network Working Group M. Rose
Request for Comments: 1283 Dover Beach Consulting, Inc.
Obsoletes: RFC1161 December 1991
SNMP over OSI
Status of this Memo
This memo defines an EXPerimental Protocol for the Internet
community. Discussion and suggestions for improvement are requested.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
Distribution of this memo is unlimited.
Table of Contents
1. Background ............................................ 1
1.1 A Digression on User Interfaces ...................... 2
1.1.1 Addressing Conventions for UDP-based service ....... 3
1.2 A Digression of Layering ............................. 3
2. Mapping onto CLTS ..................................... 3
2.1 Addressing Conventions ............................... 4
2.1.1 Conventions for CLNP-based service ................. 4
3. Mapping onto COTS ..................................... 4
3.1 Addressing Conventions ............................... 5
3.1.1 Conventions for TP4/CLNP-based service ............. 5
3.1.2 Conventions for TP0/X.25-based service ............. 6
4. Trap PDU .............................................. 6
5. Acknowledgements ...................................... 7
6. References ............................................ 7
7. Security Considerations................................ 8
8. Author's Address....................................... 8
1. 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.
1.1. 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.
1.1.1. 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.
1.2. 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.
2. Mapping onto CLTS
Mapping the SNMP onto the CLTS is straight-forward. The elements of
procedure are identical to that of using the UDP, with one exception:
a slightly different Trap PDU is used. Further, 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.
2.1. 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.
2.1.1. 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.
3. 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. Further, a slightly different Trap PDU is used.
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.
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 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.
3.1.1. 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.
3.1.2. 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
This is the X.25 protocol-ID assigned for local management purposes.
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
This is an X.25 protocol-ID assigned for local purposes.
4. Trap PDU
The Trap-PDU defined in [1] is designed to represent traps generated
on IP networks. As such, a slightly different PDU must be used when
representing traps generated on OSI networks.
RFC1283 DEFINTIONS ::= BEGIN
IMPORTS
TimeTicks
FROM RFC1155-SMI -- [2] --
VarBindList
FROM RFC1157-SNMP -- [1] --
ClnpAddress
FROM CLNS-MIB -- [9] --;
Trap-PDU ::=
[4]
IMPLICT SEQUENCE {
enterprise -- type of object generating
OBJECT IDENTIFIER, -- trap, see sysObjectID
agent-addr -- address of object generating
ClnpAddress, -- trap
generic-trap -- generic trap type
INTEGER {
coldStart(0),
warmStart(1),
linkDown(2),
linkUp(3),
authenticationFailure(4),
egpNeighborLoss(5),
enterpriseSpecific(6)
},
specific-trap -- specific code, present even
INTEGER, -- if generic-trap is not
-- enterpriseSpecific
time-stamp -- time elapsed between the last
TimeTicks, -- (re)initialization of the
-- network entity and the
-- generation of the trap
variable-bindings -- "interesting" information
VarBindList
}
END
5. Acknowledgements
The predecessor of this document (RFC1161) was produced by the SNMP
Working Group, and subsequently modified by the editor to reflect
operational experience gained since the original publication.
6. References
[1] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "A Simple
Network Management Protocol (SNMP)", RFC1157, 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", RFC1155,
Performance Systems International, Hughes LAN Systems, May 1990.
[3] McCloghrie K., and M. Rose, Editors, "Management Information Base
for Network Management of TCP/IP-based internets", RFC1213,
Hughes LAN Systems, Performance Systems International, March
1991.
[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", RFC768, USC/Information
Sciences Institute, November 1980.
[7] Kille, S., "A String Encoding of Presentation Address", RFC1278,
Department of Computer Science, University College London,
November 1991.
[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.
[9] Satz, G., "CLNS MIB for use with CLNP and ES-IS", RFC1238, cisco
Systems, June 1991.
7. Security Considerations
Security issues are not discussed in this memo.
8. Author's Address
Marshall T. Rose
Dover Beach Consulting, Inc.
420 Whisman Court
Mountain View, CA 94043-2112
Phone: (415) 968-1052
Email: mrose@dbc.mtview.ca.us
X.500: mrose, dbc, us
