Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 343
Agent

Agents are simple elements that have access to a network’s elements (router, switch, PC, etc.) MIB. Agents are the interface from the network management server to the client MIB. They perform server-requested functions. When a server requests information from a client, it will build its SNMP request (explained in a moment) and send it, unicast, to the client. The agent receives this request, processes it, retrieves or sets the information in the MIB of the client, and generates some type of response to the server. Usually, agents only transmit information when requested by a server. However, there is one instance in which an agent will transmit unsolicited information. It is known as a trap.

There are certain things on a network station that may force it to immediately notify the server. Some of these traps are defined by the RFC. Things such as cold/warm start and authentication failure are traps that are sent to the server. Most agent applications today permit the use of user-defined traps. This means that the network administrator of an SNMP compliant device can configure the router to send traps to the server when certain conditions are met. For example, a router may send a trap to the server when its memory buffers constantly overflow or when too many ICMP redirects have been sent.

Another type of agent is known as the proxy agent. This allows one station to become an agent for another network station that does not support SNMP. Basically, proxy agents server as translators between servers and non-SNMP capable clients (for security, limited resources, etc.).

Agent