Using SNMP to Monitor Servers

Simple Network Management Protocol, an application level, IP-based protocol, is the most widely used network discovery and monitoring technology around, with most hardware manufacturers providing SNMP enabled devices.

Management Information Base (MIB)

At the core of the SNMP technology is the Management Information Base (MIB). MIB are database-like structures in each device, containing device-related information stored as variables and definitions – for instance, a router’s MIB would contain network traffic and forwarding information; a switch’s MIB would contain spanning tree, VLAN, bridging information; a server’s MIB might contain data on CPU, memory utilization, location, uptime and so on. Each object in the MIB is identified by a Unique Object Identifier (OID).

How SNMP Works

SNMP works by exchanging SNMP information between SNMP managers and agents. The manager is a software module present in the network management tool, while the agent software is embedded by vendors into network devices. Using SNMP queries, and by studying the replies sent by the agent software, the manager first identifies and locates the devices. It then periodically polls the devices, and obtains device-related information. The network monitoring tool then records and analyses the information to monitor device performance and health. Additionally, SNMP allows remote device configuration through SNMP control commands. Administrators can also set up “SNMP traps” – data packages sent to the manager when a user-defined threshold is reached. Traps trigger alarms in the network management tool, which can be configured to send email/SMS notifications to the administrator.

SNMP can comprehensively monitor not only the network elements like routers and switches, but can also be used to monitor network servers. Details like server hardware description, physical location, IP address, available disk space and server uptime can be monitored through SNMP. In addition, software details like version, installed application, services (WINS, DHCP, IIS etc), dependencies, are all available as MIB values. SNMP can also monitor disk spaces, resource (memory/CPU) utilization, local users, shares and disk volumes. Along with physical servers, virtual servers to benefit from SNMP. VMware ESX servers, for instance, contain an embedded SNMP agent which allows administrators to poll request and set up traps.

WhatsUp Gold network management suite uses SNMP (and Telnet, WMI and SSH) to monitor servers. It can monitor SNMP v1, v2, v3 enabled servers across operating systems including Windows, Linux and Unix. The suite also comes with web-based SNMP tools including the MIB Walker (to assess device support), MIB Manager (to identify MIB errors) and MIB explorer (to validate the MIBs).