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Chapter 21 Network Management: SNMP Objectives Upon completion you will be able to: • Understand the SNMP manager and the SNMP agent • Understand the roles of SMI and MIB in network management • Be familiar with SMI object attributes and encoding methods • Know how an MIB variable is accessed • Be familiar with the SNMP PDU and format TCP/IP Protocol Suite 1 21.1 CONCEPT SNMP defines a manager, usually a host, that controls and monitors a set of agents, usually routers. The topics discussed in this section include: Managers and Agents TCP/IP Protocol Suite 2 Figure 21.1 TCP/IP Protocol Suite SNMP concept 3 21.2 MANAGEMENT COMPONENTS SNMP requires the use of two other protocols: Structure of Management Information (SMI) and Management Information Base (MIB). Network management on the Internet is done through the cooperation of SNMP, SMI, and MIB. The topics discussed in this section include: Role of SNMP Role of SMI Role of MIB An Analogy An Overview TCP/IP Protocol Suite 4 Figure 21.2 TCP/IP Protocol Suite Components of network management on the Internet 5 Note: SNMP defines the format of packets exchanged between a manager and an agent. It reads and changes the status (values) of objects (variables) in SNMP packets. TCP/IP Protocol Suite 6 Note: SMI defines the general rules for naming objects, defining object types (including range and length), and showing how to encode objects and values. SMI defines neither the number of objects an entity should manage, nor names the objects to be managed nor defines the association between the objects and their values. TCP/IP Protocol Suite 7 Note: MIB creates a collection of named objects, their types, and their relationships to each other in an entity to be managed. TCP/IP Protocol Suite 8 Note: We can compare the task of network management to the task of writing a program. ❏ Both tasks need rules. In network management this is handled by SMI. ❏ Both tasks need variable declarations. In network management this is handled by MIB. ❏ Both tasks have actions performed by statements. In network management this is handled by SNMP. TCP/IP Protocol Suite 9 Figure 21.3 TCP/IP Protocol Suite Management overview 10 21.3 SMI SMI is a component used in network management. It names objects, defines the type of data that can be stored in an object, and shows how data can be encoded for transmission over the network The topics discussed in this section include: Name Type Encoding Method TCP/IP Protocol Suite 11 Figure 21.4 TCP/IP Protocol Suite Object attributes 12 Figure 21.5 TCP/IP Protocol Suite Object identifier 13 Note: All objects managed by SNMP are given an object identifier. The object identifier always starts with 1.3.6.1.2.1. TCP/IP Protocol Suite 14 Figure 21.6 TCP/IP Protocol Suite Data type 15 Table 21.1 Data types TCP/IP Protocol Suite 16 Figure 21.7 TCP/IP Protocol Suite Conceptual data types 17 Figure 21.8 TCP/IP Protocol Suite Encoding format 18 Table 21.2 Codes for data types TCP/IP Protocol Suite 19 Figure 21.9 TCP/IP Protocol Suite Length format 20 Example 1 Figure 21.10 shows how to define INTEGER 14. See Next Slide TCP/IP Protocol Suite 21 Figure 21.10 TCP/IP Protocol Suite Example 1, INTEGER 14 22 Example 2 Figure 21.11 shows how to define the OCTET STRING “HI.” See Next Slide TCP/IP Protocol Suite 23 Figure 21.11 TCP/IP Protocol Suite Example 2, OCTET STRING “HI” 24 Example 3 Figure 21.12 shows how to define ObjectIdentifier 1.3.6.1 (iso.org.dod.internet). See Next Slide TCP/IP Protocol Suite 25 Figure 21.12 TCP/IP Protocol Suite Example 3, ObjectIdentifier 1.3.6.1 26 Example 4 Figure 21.13 shows how to define IPAddress 131.21.14.8. See Next Slide TCP/IP Protocol Suite 27 Figure 21.13 TCP/IP Protocol Suite Example 4, IPAddress 131.21.14.8 28 21.4 MIB MIB is a component used in network management. Each agent has its own MIB, a collection of all the objects that the manager can manage. The topics discussed in this section include: Accessing MIB Variables Lexicographic Ordering TCP/IP Protocol Suite 29 Figure 21.14 TCP/IP Protocol Suite mib-2 30 Figure 21.15 TCP/IP Protocol Suite udp group 31 Figure 21.16 TCP/IP Protocol Suite udp variables and tables 32 Figure 21.17 TCP/IP Protocol Suite Indexes for udpTable 33 Figure 21.18 TCP/IP Protocol Suite Lexicographic ordering 34 21.5 SNMP SNMP is an application program that allows 1) a manager to retrieve the value of an object defined in an agent; 2) a manager to store a value in an object defined in an agent; and 3) an agent to send an alarm message about an abnormal situation to the manager The topics discussed in this section include: PDUs Format TCP/IP Protocol Suite 35 Figure 21.19 TCP/IP Protocol Suite SNMP PDUs 36 Figure 21.20 TCP/IP Protocol Suite SNMP PDU format 37 Table 21.3 Types of errors TCP/IP Protocol Suite 38 21.6 MESSAGES A message in SNMP is made of four elements: version, header, security parameters, and data (which includes the encoded PDU). TCP/IP Protocol Suite 39 Figure 21.21 TCP/IP Protocol Suite SNMP message 40 Table 21.4 Codes for SNMP messages TCP/IP Protocol Suite 41 Example 5 In this example, a manager station (SNMP client) uses the GetRequest message to retrieve the number of UDP datagrams that a router has received. There is only one VarBind entity. The corresponding MIB variable related to this information is udpInDatagrams with the object identifier 1.3.6.1.2.1.7.1.0. The manager wants to retrieve a value (not to store a value), so the value defines a null entity. Figure 21.22 shows the conceptual view of the packet showing the hierarchical nature of sequences. We have used white and color boxes for the sequence and a gray one for the PDU. See Next Slide TCP/IP Protocol Suite 42 Example 5 The VarBind list has only one VarBind. The variable is of type 06 and length 09. The value is of type 05 and length 00. The whole is a sequence of length 0D (13). The VarBind list is also a sequence of length 0F (15). The GetRequest PDU is of length 1D (29). Now we have three OCTET STRINGs related to security parameter, security model, and flags. Then we have two integers defining maximum size (1024) and message ID (64). The header is a sequence of length 12, which we left blank for simplicity. There is one integer, version (version 3). The whole message is a sequence of 52 bytes. Figure 21.23 shows the actual message sent by the manager station (client) to the agent (server). See Next Slide TCP/IP Protocol Suite 43 Figure 21.22 TCP/IP Protocol Suite Example 5 44 Figure 21.23 TCP/IP Protocol Suite GetRequest message 45 21.7 UDP PORTS SNMP uses the services of UDP on two well-known ports, 161 and 162. The well-known port 161 is used by the server (agent), and the wellknown port 162 is used by the client (manager). TCP/IP Protocol Suite 46 Figure 21.24 TCP/IP Protocol Suite Port numbers for SNMP 47 21.8 SECURITY The main difference between SNMPv3 and SNMPv2 is the enhanced security. SNMPv3 provides two types of security: general and specific. SNMPv3 provides message authentication, privacy, and manager authorization. TCP/IP Protocol Suite 48