3Com 3C15500 - Network Director User Manual page 711

Configuration 707
response monitoring for all other devices. The importance of a device is
based upon its features and links, but not upon its physical location
within the network. It also automatically selects the poll rates for the
monitored devices, based upon the number of devices in the map and
not upon their location.
As a result, using automatic monitoring mode in a multi-site network may
result in many or all of your remote devices being monitored in full
monitoring mode. This can cause a large amount of monitoring traffic to
be generated over the WAN links, which may result in increased latency
to the remote sites, or even oversubscription of the WAN links. This can
be further exacerbated if the selected poll rate causes the remote devices
to be polled frequently.
3Com recommends that, when monitoring a multi-site network, you do
not use automatic monitoring mode. Instead it is recommended that you
manually tune the monitoring of your network based upon locality and
importance of the devices.
Before you can do this you will need to determine suitable monitoring
modes and poll rates for the devices in your network. The exact settings
for your network will depend upon your individual monitoring
requirements. However, the following pointers may be used to guide
your decision:
Where possible, use either the response monitoring for remote devices.
While response monitoring still polls remote devices, it generates very
little traffic with each poll and so can greatly decrease the amount of
traffic generated on your WAN links when compared with full monitoring
mode.
SNMP traps only monitoring mode generates even less traffic than
response monitoring mode, as traffic is only generated when there is a
problem with the device. However, SNMP traps only monitoring mode
does not allow 3Com Network Director to determine when the device
has stopped responding, and so can delay remedial action.
Note that active monitoring (i.e. the full monitoring and response
monitoring modes) poll on a regular basis. If a particular remote site is
accessed via a dial-on-demand link then active monitoring may force this
link to be permanently active or, at the very least, will cause the link to be
re-established on a regular basis.