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[edit] Network Management Systems

Network Management Systems (or NMS) generally refers to a Client-server system that delivers relevant network information. This information can be as simple as one PC connected to a printer, or as complex as the whole internet itself.

Historically, NMS was a requirement that came about with the introduction of networked computing, to facilitate the correction of network problems.

Today it has evolved to maintain its' original purpose, as well as delivering commercial information to both internal and external parties of the network under monitoring.

The two rudimentary methods that NMS use to obtain information, is

i) Polling of devices from an external source and

ii) Receipt of information from the device

External Polling

Monitoring of networked devices by an external source is achieved by using a system of Inter-Process Communication (IPC). The Simple Network Management Protocol (SNMP) process is the most common method of polling devices.

Here, an SNMP process running on the server is configured to communicate with an SNMP agent process running on the monitored device. Many devices come pre-configured with SNMP agents, and all that is required for polling to occur is to configure both the server and agent to communicate.

This configuration focuses around security, and both the server and client are configured with the same key strings, also known as the SNMP community strings. The server must also be able to reach the client, and although not universal, in most instances this is done via IP Routing.

Examples Of SNMP Polling

Excluding PCs, the internet's most basic components are

i) Inter-networking devices (such as routers, switches and modems) and

ii) A media on which to transport binary information between routers and switches e.g. wired media, wireless media, fibre-optics.

These two components meet at an interface. Generally, this interface has a physical limitation as to how much binary information can be passed in a given period. A commonly known example of this would be broadband connections for home internet users, usually specified in Megabits per second.

There may be a requirement for someone to know the rate at which data is passing through this interface, and to compare it to the physical limitation of the interface (also known as the utilization of the interface). If the utilization approaches 100% in the given polling period, there is a likeliehood that users (located "behind" the interface) may be experiencing problems.

SNMP will poll the device that houses the interface, and obtain a counter reading for a specific interface (or all interfaces) for that device. This information is then stored.

With periodic polling of the same interface, a historical graph of interface utilization can be re-constructed from the data, giving an indication of usage, and determining if the interface needs to be upgraded (or downgraded in the case of under-utilized interfaces).

Interface statistics are only one of many statistics that can be polled for. Other common information polled for include CPU Utilization, Interface Errors, Usage information for users of systems, etc.

SNMP Polling is not restricted to routers, switches and modems. SNMP agents can be embedded on just about every device on the internet including PCs and printers.

Reference should also be made to the ability to reset a device's settings using SNMP. SNMP community strings are usually configured in pairs. The read-only SNMP Community string will allow the server to read information whereas the read-write SNMP Community string will also allow a parameter on a device to be re-configured e.g. most devices contain a text string describing the location of a device, and this is re-configurable using SNMP.

Management Information Base

Management Information Bases (or MIBs) are simply numeric references used by the SNMP polling process to identify what is being polled.

The manufacturer of a device may choose to use the publically published MIBs (known as MIB II) or they may choose to design and write their own MIB agents in their device (enterprised based MIBs), and supply this to the purchaser of the device. Most SNMP servers are able to be configured to poll specific MIBs, although most come with the MIB II definitions already pre-defined.

IANA is the international organisation that takes responsibility for maintaining MIB definitions.

Interface polling, as described above, has several MIBs available for SNMP servers to use.