Notes on SMNP

Networks have a bad habit of failing. This makes network management an extremely important task. Because protocols (such as TCP) will correct lost or damaged frames, intermittent hardware or software failures can be difficult to detect. While the system may continue to operate despite failures, performance can suffer.

Most networks are heterogeneous, composed of equipment from many different vendors. A network management system has to be standardized and supported by a wide variety of equipment to be useful. The Simple Network Management Protocol is a system for communicating with network components that is useful in locating network problems. SNMP is an application layer protocol. It uses the well-known client server model although it calls the clients "managers" and the servers are "agents". SNMP data travels the network just like any other user data. The Internet Protocol does not have any network management functionality built into it.

All sorts of network components (such as hubs, switches, routers, repeaters and bridges) support SNMP agents. These programs maintain a set of variables (called objects) that describe the status of the device. The agents are programmed to record interesting values and counters in these variables. Some variables might count the number of incorrect CRCs received or the number of packets sent.

SNMP uses a fetch-store paradigm. Management software on a host computer can fetch statistical counters from managed devices. Management software can reset the counters by storing a zero in the object. Storing values in certain objects can direct the device to take certain actions, such as disable a line or reboot.

In order to receive an SNMP message, which is sent using the Internet Protocol, a device must have a hardware address and an Internet address. This is normal for devices such as gateways and routers, but throughout the semester we have stated that repeaters and bridges do not have Internet addresses. In actuality, managed devices have IP addresses for the sole purpose of network management. Messages sent to the IP address of a bridge are intended for the bridge SNMP agent and are not intended to be sent to another network segment.

Data items are encoded according to the Abstract Syntax Notation.1 (ASN.1) standard.

The collection of all data objects that an SNMP manager can access is known as a Management Information Base. SNMP does not define the database. It only defines the message format and how messages are encoded. ASN.1 defines long hierarchical names for the data objects which are translated to a more compact numeric representation for transmission.