SNMP

The Simple Network Management Protocol, or SNMP, is a collection of protocols that are designed to facilitate the monitoring and management of network resources. SNMP is not a WebLogic-specific product; actually, it predates the entire company by a couple of decades.

The SNMP protocol has been steadily refined over the years to arrive at its present almost-usable state. The protocol as a whole is primarily defined in RFCs 1155, 1156, 1157 and expanded in a couple of dozen other RFCs.

Generally speaking, SNMP systems have a centralized manager not the WebLogic server managerwhich keeps an eye on one or more agents . In the context of WebLogic, the role of SNMP agent is fulfilled by one or more WebLogic servers with their SNMP component enabled. These agents pass information on to the SNMP manager in response to two types of circumstances:

Poll requests	The SNMP manager makes a routine request for information about resources that it manages .
Traps	The SNMP agent, acting on its own initiative and not in response to a poll from its manager, reports some condition that you (the administrator) have configured it (the agent) to regard as noteworthy.

MIB

The SNMP protocol defines a fairly rigid set of standards for the nature of the information that can be passed to a server. In particular, you're not just passing over raw lines from a log file, or the output from a script, or whatever. SNMP managers require that their agents pass over information in the form of dotted number strings. These number strings, collectively referred to as Management Information Bases or MIBs, define a hierarchy of network resources.

To give the idea some flavor, I'll provide a little more explanation, even though it's not strictly relevant to our purposes. A number of more or less standard MIBs are available in the public domain to monitor generic network attributes. Here's one example, taken from RFC-1213:

sysUpTime	1.3.6.1.2.1.1.3
Keeps track of the time elapsed since the network management software was last initialized .

Not all MIBs are publicly available, or need to be. The MIB hierarchy is infinitely extensible. Most vendors of network equipment and software define their own proprietary MIBs. Again, recall that this is strictly on the agent sidein order to actually use the agent to monitor anything, you must first purchase an SNMP manager, upload all the relevant MIBs, ^[2] and figure out what to do with the information. (See Figure 9-2.)

^[2] As anyone who has actually gone through the process will tell you, implementing SNMP is much easier said than done. Compatibility problems between SNMP managers and agents are not infrequent.

Figure 9-2. SNMP Manager

BEA is no exception, and why should it be? Developing an MIB agent is a relatively quick and inexpensive method for providing a bullet point for sales meetings. BEA's MIB is registered at .1.3.6.1.4.1.140.

Like things WebLogic, SNMP management is done at the level of the domain. The SNMP manager interacts with a WebLogic Administration server. In a single-server domain, the Administration server simply relays any relevant information passed on from its Managed servers. In a multiple-server domain, a single Administration server can be used as a point of collection for all SNMP information.