TCP/IP 详解 卷1 ch25 SNMP:简单网络管理协议

1. 基于TCP/IP的网络管理包含3个部分：
1） MIB， specifies what variables the network elements maintain (the information that can be queried and set by the manager).包含所有代理进程的所有可以查询和修改的参数
2） SMI， A set of common structures and an identification scheme used to reference the variables in the MIB
3） SNMP，The protocol between the manager and the element, called the Simple Network Management Protocol (SNMP).

2. SNMP
5 messages
1) get-request
2) get-next-request
3) set-request
4) get-response
5) trap
The first three messages are sent from the manager to the agent, and the last two are from the agent to the manager.The manager sends its three requests to UDP port 161. The agent sends traps to UDP port 162. using ASN1 and BER encoding rule.

3. Object Identifier
An object identifier is a data type specifying an authoritatively named object. An object identifier is a sequence of integers separated by decimal points.All variables in the MIB start with the object identifier 1.3.6.1.2.1

Case Diagrams visually illustrate the relationships between the various MIB variables in a given group.

4. Instance Identification

1) Simple variables are referenced by appending ".0" to the variable's object identifier.
2) Tables
All the entries in MIB tables are lexicographically ordered by their object identifiers. tables are accessed in a column-row order.

5. 应用举例
1） 接口MTU
2） 路由表