3Com 3C15500 - Network Director - PC, Руководство пользователя, Страница: 282 / 924

278 C
HAPTER
7: M
ONITORING THE
N
ETWORK
Service Polling
3Com Network Director provides support for monitoring the status of
various services that may be provided by servers in your network,
including such services as DNS, FTP, POP3 and SMTP mail.3Com Network
Director monitors a service by connecting to and sending a request to the
service on a regular basis.The response received, or the lack of any
response, is used by 3Com Network Director to update the state of the
monitor.
Depending upon the service being monitored, the monitor may be able
to use the response to determine more than just the responsiveness of
the service i.e. how quickly the response is received.Some services, such
as DNS, support status requests to which they respond with details of the
internal status of the service. 3Com Network Director will use these status
requests when they are available to provide more detailed information
about the service status.
SNMP Trap Receipt
Network infrastructure devices that maintain statistics about their
operation and allow access to this information via SNMP MIBs often also
support the concept of SNMP traps.SNMP traps are unsolicited messages
sent out by the devices when the data stored in the SNMP MIB indicates
that the device is in certain states.These may indicate simple state
changes such as a port going up or down, or may indicate more complex
state changes, such as the received packet rate reaching a particular level.
Devices that support SNMP traps are known as trap sources.In order for
another device to receive the SNMP traps from a trap source it must
register with the trap source as a trap destination.When a trap source
enters a state for which it will generate an SNMP trap it sends the trap to
all registered trap destinations.
SNMP trap receipt is the only passive monitoring technique used by
3Com Network Director. 3Com Network Director optionally registers the
PC it is running on as a trap destination with all monitored network
infrastructure devices that support SNMP traps. When 3Com Network
Director receives an SNMP trap it determines whether or not it has a
monitor associated with the trap type.If it does then the trap is used to
update the state of the monitor.