Another technique that the administrator can use to manage and monitor the
network is to employ the Simple Network Management Protocol (SNMP). SNMP is an
application-layer protocol that facilitates the exchange of management
information between network devices. It is part of the TCP/IP protocol suite.
SNMP enables network administrators to manage network performance, find and
solve network problems, and plan for network growth. SNMP can be used to manage
Cisco routers, switches, wireless access points, firewalls, printers, servers
and other SNMP capable devices
.
There are
three versions of SNMP, as shown in Figure
. SNMPv1
and SNMPv2 have features in common, but SNMPv2 offers enhancements, such as
additional protocol operations. SNMPv3 adds administration and security
features. This section provides descriptions of the SNMPv3 protocol operations.
Cisco recommends disabling SNMP if not in use or use version 3.
Figure
illustrates a
basic network managed by SNMP.
SNMP Key Terms
In order to
understand SNMP support in Cisco devices, it is important to understand the
SNMP-related terminology discussed in Figure
.
SNMP
Basic Components
An SNMP managed network consists of three key
components:
- Managed devices
- Agents
- Network management systems (NMSs)
A managed device is a network node that contains an SNMP agent and
resides on a managed network. Managed devices collect and store management
information and make this information available to NMSs using SNMP. Managed
devices, sometimes called network elements, can be routers, switches, wireless
access points, firewalls, printers, servers and other SNMP capable devices.
An agent is a network management software module that resides in a managed
device
. An agent has
local knowledge of management information and translates that information into
a form compatible with SNMP.
An NMS executes applications that monitor
and control managed devices
. NMSs provide
the bulk of the processing and memory resources required for network
management. One or more NMSs must exist on any managed network. SNMP management
applications, such as CiscoWorks2000, communicate with agents to get statistics
and alerts from the managed devices.
SNMP Basic
Commands
Managed devices are monitored and controlled using basic SNMP
commands, as shown in Figure
:
- The read command is used by an NMS to monitor managed
devices. The NMS examines different variables that are maintained by managed
devices.
- The write command is used by an NMS to control managed
devices. The NMS changes the values of variables stored within managed
devices.
- Managed devices to asynchronously report events to the NMS use the
trap command. When certain types of events occur, a managed
device sends a trap to the NMS.
- Traversal operations are used by the NMS to determine which variables a
managed device supports and to sequentially gather information in variable
tables, such as a routing table.
The basic SNMP process is shown in Figure
.