Q. What is SNMP?
A. SNMP stands for the Simple Network Management Protocol. At its heart, SNMP is a set of rules that allows a computer to get statistics from another computer across the Internet.
Computers keep track of various statistics that measure what they're doing. For example, routers can keep track of the number of bytes, packets, and errors that were transmitted and received on each interface (port). Web servers might keep a tally of the number of hits they have received. Other kinds of equipment have configuration information that's available through SNMP.
Each of these pieces of information (packet statistics, page hits, configuration) is kept in a database described by a Management Information Base (a MIB in SNMP parlance.) There are a many different MIBs, describing many different aspects of a computer's operation.
The various values that can be retrieved from a MIB are called MIB variables. These variables are defined in the MIB for a device. Each MIB variable is named by an Object Identifier (OID), which usually has a name in the form of numbers separated by periods ("."), like this: 18.104.22.168.xxxx.x.x.x.x...
For example, the MIB-II (pronounced, "MIB two") has a variable that indicates the number of interfaces (ports) in a router. It's called the "ifNumber", and its OID is 22.214.171.124.126.96.36.199.0
InterMapper, as well as many other network monitoring tools, can query a device for the MIB variables and display the results. When a device receives a SNMP Get-Request for this ifNumber OID, it responds with the count of interfaces.
Note: The trailing ".0" in the example above is technically part of the OID. Although you will often see OIDs written without it, InterMapper requires that it be present wherever you enter an OID.