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The SNMP general message format was, of course, first used to define the format of messages in the original SNMP Protocol, SNMP version 1 (SNMPv1). This first version of SNMP is probably best known for its relative simplicity, compared to the versions that followed it. This is reflected in its message format, which is quite straight-forward.
The general message format in SNMPv1 is a “wrapper” consisting of a small header and an encapsulated PDU. Not very many header fields were needed in SNMPv1 because the community-based security method in SNMPv1 is very rudimentary. Thus, the short overall format for SNMPv1 messages shown in Table 212 and Figure 277.
Table 212: SNMP Version 1 (SNMPv1) General Message Format
Field Name
Syntax
Size (bytes)
Description
Version
Integer
4
Version Number: Describes the SNMP version number of this message; used for ensuring compatibility between versions. For SNMPv1, this value is actually 0, not 1.
Community
Octet String
Variable
Community String: Identifies the SNMP community in which the sender and recipient of this message are located. This is used to implement the simple SNMP community-based security mechanism
PDU
—
Variable
Protocol Data Unit: The PDU being communicated as the body of the message.
Figure 277: SNMP Version 1 (SNMPv1) General Message Format