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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)            9  TCP/IP Network Management Framework and Protocols (SNMP and RMON)                 9  TCP/IP Simple Network Management Protocol (SNMP) Protocol                      9  SNMP Protocol Messaging and Message Formats

SNMP Message Field Definitions, General Message Format and Message Sections 1 2 3 SNMP Version 2 (SNMPv2) Message Formats

SNMPv1 PDU Formats

All of the PDUs in SNMPv1 have the same format, with one exception: Trap-PDU. The exact semantics of each field in the PDU depends on the particular message. For example, the ErrorStatus field only has meaning in a reply and not a request, and object values are used differently in requests and replies as well.

Table 213 and Figure 278 show the common format for most of the SNMPv1 PDUs: GetRequest-PDU, GetNextRequest-PDU, SetRequest-PDU and GetResponse-PDU:

Table 213: SNMP Version 1 (SNMPv1) Common PDU Format

Field Name	Syntax	Size (bytes)	Description
PDU Type	Integer (Enumerated)	4
Request ID	Integer	4	Request Identifier: A number used to match requests with replies. It is generated by the device that sends a request and copied into this field in a GetResponse-PDU by the responding SNMP entity.
Error Status	Integer (Enumerated)	4
Error Index	Integer	4	Error Index: When Error Status is non-zero, this field contains a pointer that specifies which object generated the error. Always zero in a request.
Variable Bindings	Variable	Variable	Variable Bindings: A set of name-value pairs identifying the MIB objects in the PDU, and in the case of a SetRequest-PDU or GetResponse-PDU, containing their values. See the general message format topic for more on these bindings.

Figure 278: SNMP Version 1 (SNMPv1) Common PDU Format

SNMP Message Field Definitions, General Message Format and Message Sections 1 2 3 SNMP Version 2 (SNMPv2) Message Formats

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