Purposes Of Network Monitoring; Testing Static Routes - HP 7102dl - ProCurve Secure Router Configuration Manual

Network Monitoring
Overview
9-6

Purposes of Network Monitoring

Now that you understand how network monitoring works, you can learn about
the services it provides to your WAN.

Testing Static Routes

A static route has a low administrative distance, based on the assumption that
the person who created the route can vouch for its accuracy and preferred
status.
However, static routes do not always remain accurate. If one of the ProCurve
Secure Router's own interfaces goes down, the router immediately stops using
any route associated with that interface. However, links can fail at any point
along a route; without dynamic routing, the local router has no way to know
that the traffic that it continues to forward can no longer reach its destination.
For example, your ProCurve Secure Router may connect to the Internet
through its Ethernet connection and a cable modem. The router's Ethernet
interface stays up even if the modem's connection fails. As far as the router is
concerned, its static route to the Internet is good, but traffic cannot reach its
destination.
Network monitoring is a mechanism for testing static routes and removing
those routes that fail the test. Thus static routing becomes more like dynamic
routing, in that it can respond to failed network connections.
However, network monitoring does not help the router learn new routes. If
you want the router to switch to an alternate route if the primary route fails,
you must take one of these steps in advance:
You enter the alternate route or routes and enable load sharing.
More commonly, you create a floating static route (an alternate route with
a higher administrative distance than the primary route). A common use
for network monitoring is to create a floating route through a demand
interface. If the ProCurve Secure Router cannot reach a key destination
(such as a server at the company headquarters), the ProCurve Secure
Router places a call to establish an Integrated Services Digital Network
(ISDN) connection.
Figure 9-1 shows an example of a WAN that uses network monitoring to
detect when to establish a backup ISDN connection to the Internet service
provider (ISP). When the probe fails to reach the vital headquarters'
server, the track removes the primary route through the cable modem,
and the floating static route becomes active.