This section provides additional information about the Simple Network Management Protocol (SNMP) architecture, the SNMP management information base (MIB), and some additional MIB concepts.
In an SNMP architecture, a manager component manages an agent. The agent is software that runs on a network device or application, responds to information requests (SETs and GETs), and then generates autonomous notifications called traps. The manager is software that receives the traps and that provides a mechanism to SET or GET SNMP objects from the network device.
To receive autonomous traps, the manager runs an application that listens on the TCP/IP SNMP trap port (port 162). SNMP SETs and GETs use port 161. This application is typically called a Trapd, or trap daemon. A trap daemon is a process that runs in the background and handles a service on a computer. The Netcool Trapd application is called the SNMP Probe (nco_p_mttrapd, where mt is an abbreviation of multithreaded) and is located in the $OMNIHOME/probes/ directory. The rules files generated by MIB Manager are designed to be used by the SNMP Probe.
Basic security in SNMP v1 and v2 is provided by using community strings. Community strings are plain text passwords that are sent with all requests. There are separate community strings for read-only access and read-write access. MIB Manager must know the community string defined on a device before it can execute any requests (read-only for a GET and read-write for a SET), and SNMP traps and notifications are sent to MIB Manager with a predefined community string.
All network devices that support SNMP have a mechanism for defining the community string. The standard default read-only password is public and the standard default read-write password is private. If no community string has been set on a device, it will usually be one of these passwords. For security reasons, the default passwords must be changed as soon as possible.
For a discussion of ASN.1 and the Basic Encoding Rules (BER) that are used for encoding SNMP data into Protocol Data Unit (PDU) packets for transmission on the network, see the following book:
SNMP, SNMPv2, and CMIP: The Practical Guide to Network-Management Standards by William Stallings (Addison-Wesley, 1993).