RFC 1207:FYI on Questions and Answers: Answers...
RFC-Ref

PDU


Click on the red underlined text to get to the source

... 6] I find mention of authentication of PDUs. Are there any standards for authentication mechanisms? ...
... valid value that the variable may be set to is "reset" (which is returned in the get response PDU) and at all other times a get/getnext will respond with "not-reset". ...



Google
Web
RFC-Ref