|Email This Page
SNMPv1: Simple Network Management Protocol version 1
Simple Network Management Protocol (SNMP ) is the protocol developed to manage nodes (servers, workstations, routers, switches and hubs etc.) on an IP network. SNMP is an application protocol, which is encapsulated in UDP . The general SNMP information can be found in the SNMP document .
Currently, there are three versions of SNMP defined: SNMP v1, SNMP v2 and SNMP v3 . In this document, we focus on SNMPv1. SNMPv1 is a simple request/response protocol. In the SNMPv1 framework, the network-management system installed a request, and managed devices return responses.
Protocol Structure - SNMPv1 Simple Network Management Protocol version 1
The message format for all versions of SNMP is similar except PDU. The PDU (Protocol Data Unit) for SNMPv1 have five different PDU types: GetRequest, GetNextRequest, GetResponse, SetRequest, and Trap. A general description of each of these is given in the next section.
The format for GetRequest, GetNext Request, GetResponse and SetRequest PDUs is shown here.
||Object 1, value 1
||Object 2, value 2
PDU type- Specifies the type of PDU transmitted: 0 GetRequest, 1 GetNextRequest, 2 GetResponse and 3 SetRequest.
- Request ID- Associates SNMP requests with responses.
- Error status- Indicates one of a number of errors and error types. Only the response operation sets this field. Other operations set this field to zero.
- Error index- Associates an error with a particular object instance. Only the response operation sets this field. Other operations set this field to zero.
- Variable bindings- Serves as the data field of the SNMPv1 PDU. Each variable binding associates a particular object instance with its current value (with the exception of Get and GetNext requests, for which the value is ignored).
The format of the Trap PDU is shown below:
PDU type --Specifies the type of PDU (4=Trap).
- Enterprise -- Identifies the management enterprise under whose registration authority the trap was defined.
- Agent address- - IP address of the agent, used for further identification.
- Generic trap type -- Field describing the event being reported. The following seven values are defined:
- Specific trap type -- Used to identify a non-generic trap when the Generic Trap Type is enterprise specific.
- Timestamp -- Value of the sysUpTime object, representing the amount of time elapsed between the last (re-)initialization and the generation of that Trap.
SNMP , SNMPv1 , SNMPv2 , SNMPv3 , UDP , RMON , SMI, OIDs
SNMPv1 is defined by IETF (http://www.ietf.org ) in RFC 1157 plus a few supporting RFCs shown in the reference links.
http://www.javvin.com/protocol/rfc1155.pdf : Structure and Identification of Management
Information for TCP/IP based internets
http://www.javvin.com/protocol/rfc1156.pdf : Management Information Base Network
http://www.javvin.com/protocol/rfc1157.pdf : A Simple Network Management Protocol