SNMP Notes
SNMP Notes
- Agents are also known as servers and devices that will be monitored.
- Traps are event notifications that are sent to management stations.
- You need both a server side program (agent) and a client (manager or collector as I like to call it) to use it.
- Perhaps counterintuitively, the server side of SNMP represents the thing being managed, and the client side is the manager.
- Clients range from simple command-line utilities to dedicated management stations that graphically display networks and faults in eye-popping color.
- Most network hardware these days comes with an SNMP agent pre-installed
- Management Information Bases (MIBs) are structured text files that describe the data accessible through SNMP.
- MIBs contain descriptions of specific data variables, which are referred to with names known as object identifiers, or OIDs.
- An OID is just a fancy way of naming a specific managed piece of information.
- OIDs are displayed numerically, separated by periods. They are also translated to human readable format underneath. For example; the OID that refers to the uptime of the system is 1.3.6.1.2.1.1.3.
- The four basic SNMP operations are: get, get-next, set and trap.
- Get and set are the basic operations for reading and writing data to the node identified by a specific OID.
- Get-next steps through a MIB hierarchy and can read the contents of tables as well.
- A trap is an unsolicited, asynchronous notification from server (agent) to client (manager) that reports the occurrence of an interesting event or condition. This can be a multitude of things and really depends on what device its coming from.
- The simplest version of SNMP security is known as a “community string”, which is another way of saying password.
- There’s usually one community string for read only access and another for writing.
- The NET-SNMP agent is the most common package in use today. It was first created by Carnegie Mellon University.
- NET-SNMP includes an agent, some command line tools, and a server for receiving traps. It even includes some libraries to develop SNMP-aware applications.
- Usually, the default location of NET-SNMP resides in /usr/sbin/snmpd.
- The most important file is gong to be snmpd.conf.
- Below are the most commonly used tools found within NET-SNMP
snmpdelta - Monitors changes in SNMP variables over time
snmpdf - Monitors disk space on a remote host via SNMP
snmpget - Gets the value of an SNMP variable from an agent
snmpgetnext - Gets the next variable in sequence
snmpset - Sets an SNMP variable on an agent
snmptable - Gets a table of SNMP variables
snmptranslate - Searches for and describes OIDs in the MIB hierarchy
snmptrap - Generates a trap alert
snmpwalk - Traverses a MIB starting at a particular OID
- The snmpwalk command utility is great because it shows you what OIDs are available to monitor.
