SNMPv1 (RFC 1157)
The original Simple Network Management Protocol defined in RFC 1157 (May 1990). Establishes the five core PDUs (GetRequest, GetNextRequest, GetResponse, SetRequest, Trap), community-string authentication, ASN.1 message encoding, and UDP transport on ports 161 and 162. Now classified as Historic by the IETF but still widely deployed on legacy equipment.