EMG SNMP Agent 1.1 - User's Guide
2.1 SNMP Management
SNMP management is based on an agent/manager model where the agent interacts with managed devices and the manager queries, sets variables in and gets responses from one or more agents.
A managed device is typically a network device or an application that contains managed objects. These managed objects can be hardware components, configuration parameters, performance statistics and so on. Information about these objects is arranged in a Management Information Base, a MIB.
The MIB hierarchy can be depicted as a tree with a nameless root where the levels are assigned to different organizations. Each node in the tree is uniquely identified by an object identifier (OID). Nordic Messaging has been assigned the root node with OID 220.127.116.11.4.1.1194 and all EMG related objects will be descendants of that OID.
SNMP Agents can also notify managers when a specified condition arises by sending so called notifications or traps.
There are different SNMP versions: SNMP v1, v2c and version 3. Currently the EMG SNMP Agent support v1 and v2c.
2.2 The master/subagent model
Managers usually send UDP requests to an agent listening on port 161 which is the default port for SNMP. However, the same server may run multiple agents that implements different MIBs for different objects on the same server. For this the master/subagent model is used. The master agent responds to all incoming requests and is then responsible for forwarding the request to the correct agent based on the OID requested by the manager. For example on a server running Solaris, the Solaris SNMP agent may be the master agent which responds to all incoming requests. When a request related to EMG is received that request would then be forwarded to the EMG SNMP Agent which acts as a subagent.
The EMG SNMP Agent can also act as a master agent.
2.3 File system layout
EMG SNMP Agent is designed to co-exist with an EMG server installation. Therefore the SNMP Agent configuration files are located in EMGDIR/snmpd where EMGDIR defaults to /etc/emg. In this document we hereafter refer to EMGDIR/snmpd as SNMPDIR.
All directories and configuration files are created during installation based on the information entered in the installation process.
User configuration files
System configuration files
MIB definition files
The EMG SNMP Agent is licensed per server and needs a license key dependant on the hostid of the server where it will run. Usually it is the same server as the EMG server runs on. One SNMP Agent can monitor multiple EMG servers.