SNMP

Summary

The Simple Network Management Protocol (SNMP) presents true challenges to programmers writing applications that use it. Because of its complexity, many novice network programmers avoid using the protocol altogether. This chapter gives you a look under the hood of SNMP and how to build C# network programs that use SNMP to query network devices

SNMP allows network devices to maintain a database of network statistics and configuration settings. The database can be queried and manipulated using the SNMP network protocol from a remote device on the network. Each SNMP device must implement the Common Management Information Base (called MIB-II) that tracks network statistics for interfaces on the device. In addition to the common MIB, many vendors implement their own database objects to make controlling the network device from a remote workstation easy.

SNMP uses five types of command packets. The GetRequest and GetNextRequest packets are used to obtain either a single value or a series of values from the device. The GetResponse packet returns information requested in a query. The SetRequestpacket changes the value of database objects. The Trap packet is used by a network device to send an unsolicited network information packet to a central network monitoring station.

Each SNMP device uses security based on access modes and profiles. A community name is assigned access privileges in the MIB database. A remote device uses the community name as a password to query and update values in the database.

SNMP packets are difficult to create because they contain variable length information. Both the community name and MIB object included in the SNMP packet can vary in length. The SNMP commands are contained in Protocol Data Units (PDUs) that are encapsulated in the SNMP packet. Each PDU represents a single query but can contain multiple MIB objects and object values.

In this chapter, an SNMP class is created to allow programmers a single method for creating SNMP packets and sending them to remote devices. The returned response packets are forwarded to the applications for decoding.

You studied three sample network applications: a simple SNMP application to obtain system information from a network device, an application to monitor the CPU utilization of a Cisco router, and an application to obtain the MAC address table of a Cisco switch.

Next, we’ll move forward to the tricky business of Internet e-mail. The .NET network library provides a class to help the network programmer integrate Internet e-mail in network applications. Chapter 13, “SMTP,” shows how to use the .NET Mail class to send e-mail across the Internet from your program