agement packets (or messages). SNMP is a connectionless protocol that ini- tially was designed to run over a UDP/IP stack (UDP stands for User Datagram Protocol). Because of its design, it is traditionally high in overhead, with the ratio of overhead to usable data running about ten bytes to one. A typical SNMP "message" (PDU) embedded in a local network frame is shown in Figure 21.7. Inside the frame in Figure 21.7 we find an IP (Internet Protocol; see Chapter 11) datagram that has a header. The header has an IP destination address that directs the datagram to the intended recipient. Following the IP header, there is the User Datagram Protocol (UDP) that identifies the higher layer protocol process. This is the SNMP message shown in Figure 21.7 as embedded in the UDP. The application here is typically for LANs. If the IP is too long for one frame, it is fragmented (segmented) into one or more additional frames. Figure 21.8 shows a typical SNMP PDU structure that is valid for all messages but the trap format. This structure is embedded as the "message" field of Figure 21.7. The SNMP message itself is divided into two sections: (1) a version identifier plus community Local Local Network Network Header Header Header Message Trailer UDP Datagram IP Datagram Local Network Frame Figure 21.7 An SNMP "message" embedded in a local network frame. SNMP Message Version GetRequest, GetNextRequest, GetResponse Community or SetRequest PDU Request Error Error Status Index Object 1, Value 1 Object 2, Value 2 Variable Bindings Figure 21.8 An SNMP PDU structure for GetRequest, GetNext-Request, GetResponse, and Set- Response. (From Refs. 9, 13, and 14.) 21.7 NETWORK MANAGEMENT SYSTEMS IN ENTERPRISE NETWORKS name and (2) a PDU. The version identifier and community name are sometimes referred to as the SNMP authentication header. The Version field ensures that all parties in the management transaction are using the same version of SNMP protocol. We must remember the origins of SNMP evolved from TCP/IP described in Chapter 11, where w