Unformatted text preview: Chapter 21 Network Management: SNMP
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 SNMP set of agents, usually routers. set The topics discussed in this section include: Managers and Agents Managers TCP/IP Protocol Suite 2 Figure 21.1 SNMP concept TCP/IP Protocol Suite 3 21.2 MANAGEMENT COMPONENTS
SNMP requires the use of two other protocols: Structure of Management SNMP Information (SMI) and Management Information Base (MIB). Network management on the Internet is done through the cooperation of SNMP, SMI, and MIB. SMI, The topics discussed in this section include: Role of SNMP Role Role of SMI Role of MIB An Analogy An Overview
TCP/IP Protocol Suite 4 Figure 21.2 Components of network management on the Internet TCP/IP Protocol Suite 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 Management overview TCP/IP Protocol Suite 10 21.3 SMI
SMI is a component used in network management. It names objects, SMI defines the type of data that can be stored in an object, and shows how data can be encoded for transmission over the network data The topics discussed in this section include: Name Name Type Encoding Method TCP/IP Protocol Suite 11 Figure 21.4 Object attributes TCP/IP Protocol Suite 12 Figure 21.5 Object identifier TCP/IP Protocol Suite 13 Note: All objects managed by SNMP are given an object identifier. The object identifier always starts with 126.96.36.199.2.1. TCP/IP Protocol Suite 14 Figure 21.6 Data type TCP/IP Protocol Suite 15 Table 21.1 Data types Table Data TCP/IP Protocol Suite 16 Figure 21.7 Conceptual data types TCP/IP Protocol Suite 17 Figure 21.8 Encoding format TCP/IP Protocol Suite 18 Table 21.2 Codes for data types Table Codes TCP/IP Protocol Suite 19 Figure 21.9 Length format TCP/IP Protocol Suite 20 Example 1 Figure 21.10 shows how to define INTEGER 14. See Next Slide TCP/IP Protocol Suite 21 Figure 21.10 Example 1, INTEGER 14 TCP/IP Protocol Suite 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 Example 2, OCTET STRING “HI” TCP/IP Protocol Suite 24 Example 3 Figure 21.12 shows how to define ObjectIdentifier 188.8.131.52 (iso.org.dod.internet). See Next Slide TCP/IP Protocol Suite 25 Figure 21.12 Example 3, ObjectIdentifier 184.108.40.206 TCP/IP Protocol Suite 26 Example 4 Figure 21.13 shows how to define IPAddress 220.127.116.11. See Next Slide TCP/IP Protocol Suite 27 Figure 21.13 Example 4, IPAddress 18.104.22.168 TCP/IP Protocol Suite 28 21.4 MIB
MIB is a component used in network management. Each agent has its MIB own MIB, a collection of all the objects that the manager can manage. own The topics discussed in this section include: Accessing MIB Variables Accessing Lexicographic Ordering TCP/IP Protocol Suite 29 Figure 21.14 mib-2 TCP/IP Protocol Suite 30 Figure 21.15 udp group TCP/IP Protocol Suite 31 Figure 21.16 udp variables and tables TCP/IP Protocol Suite 32 Figure 21.17 Indexes for udpTable TCP/IP Protocol Suite 33 Figure 21.18 Lexicographic ordering TCP/IP Protocol Suite 34 21.5 SNMP
SNMP is an application program that allows 1) a manager to retrieve the SNMP 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 about The topics discussed in this section include: PDUs PDUs Format TCP/IP Protocol Suite 35 Figure 21.19 SNMP PDUs TCP/IP Protocol Suite 36 Figure 21.20 SNMP PDU format TCP/IP Protocol Suite 37 Table 21.3 Types of errors Table Types TCP/IP Protocol Suite 38 21.6 MESSAGES
A message in SNMP is made of four elements: version, header, security message parameters, and data (which includes the encoded PDU). parameters, TCP/IP Protocol Suite 39 Figure 21.21 SNMP message TCP/IP Protocol Suite 40 Table 21.4 Codes for SNMP messages Table Codes 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 22.214.171.124.126.96.36.199.0. 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 Example 5 TCP/IP Protocol Suite 44 Figure 21.23 GetRequest message TCP/IP Protocol Suite 45 21.7 UDP PORTS
SNMP uses the services of UDP on two well-known ports, 161 and 162. SNMP The well-known port 161 is used by the server (agent), and the wellThe known port 162 is used by the client (manager). TCP/IP Protocol Suite 46 Figure 21.24 Port numbers for SNMP TCP/IP Protocol Suite 47 21.8 SECURITY
The main difference between SNMPv3 and SNMPv2 is the enhanced The security. SNMPv3 provides two types of security: general and specific. SNMPv3 provides message authentication, privacy, and manager authorization. TCP/IP Protocol Suite 48 ...
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- Winter '10
- Simple Network Management Protocol, TCP/IP protocol suite, SMI