7.2 The Simple Network Management Protocol

Network management is a service that employs a variety of tools, applications, and devices to assist network managers in monitoring and maintaining networks. The Simple Network Management Protocol (SNMP) is one of the best-known network management technologies. SNMP has two versions: SNMP version 1 (SNMPv1) and SNMP version 2 (SNMPv2). Both versions have a common number of features. However, SNMPv2 offers enhancements, such as additional protocol operations. In the following we focus on the basics of SNMPv1 (Cisco Systems 2003).
SNMP main features (Cisco Systems 2003):

It is an application layer protocol.

It facilitates the exchange of management information between network devices.

It is part of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite.

It enables network administrators to:

Manage network performance,

Find and solve network problems, and

Plan for network growth.

7.2 The Simple Network Management Protocol

SNMP Operation: There are two main participants in SNMP. First is the manager, which is generally the 'main' station such as HP Open view. Second participant is the agent who would be the SNMP software running on a client system to be monitored (Shimonski 2005).

















Figure 2: Participants in SNMP

7.2 The Simple Network Management Protocol

SNMP Messages and Message Structure

SNMP operations are communicated between managers and agents using SNMP messages. An SNMP message in essence consists of three parts (Figure 3) (Cisco Systems 2008):

1. The SNMP version number.
2. A Community string. It must match a corresponding string that is configured at the device with the SNMP agent for the request to be accepted. Its affect is same as a password. Because this password is not encoded but sent in the clear, and because no other form of authentication of the sender takes place, SNMPv1 is considered to have very weak security.
3. The SNMP protocol data unit (PDU). This is the encoded SNMP operation itself, including a field that identifies the type of operation along with the operation parameters.

7.2 The Simple Network Management Protocol

Figure 3: SNMP Message Structure

7.2 The Simple Network Management Protocol

SNMP defines a set of five management operations, which are the primitives on which all SNMP management is based (Clemm 2007).

1. Get and get-next requests are used to retrieve management information from a Management Information Bases (MIBs).
2. Set requests are used to write to a MIB.
3. Get responses are used by agents to respond to get, get-next, and set requests.
4. Traps are used to send event messages.

All SNMP operations commonly include a parameter that is used to carry management information. The parameter contains a list of variable bindings. A variable binding is a name/value pair that consists of an OID that identifies a MIB object, and a value of that object (Clemm 2007).