Essential SNMP

Chapter 11. Extensible SNMP Agents

There will come a time when you want to extend an agent’s functionality. Extending an agent usually means adding or changing the MIBs the agent supports. Many agents that claim to support SNMP cover only a minimal number of somewhat useless MIBs -- obviously a frustrating situation for someone who is planning on doing lots of automated network management. Upgrading your software to a newer version of SNMP, say Version 2 or 3, won’t help; you won’t get any more information out of a device than if you were using SNMPv1. The newer versions of SNMP add features to the protocol (such as additional security or more sophisticated options for retrieving and setting values), but the information that’s available from any device is defined in the agent’s MIBs, which are independent of the protocol itself.

When you are faced with an agent’s limitations, you can turn to extensible agents.^[50] These programs, or extensions to existing programs, allow you to extend a particular agent’s MIB and retrieve values from an external source (a script, program, or file). In some cases, data can be returned as if it were coming from the agent itself. Most of the time you will not see a difference between the agent’s native MIBs and your extensible ones. Many extensible agents give you the ability to read files, run programs, and return their results; they can even return tables of information. Some agents have configurable options that allow you to run external programs ...