ZyXEL Communications P-870HW-I Series, User Manual

Page: 119 / 438

P-870HW-I1 User’s Guide
Chapter 7 WAN 119
C
H A P T E R
7
WAN
This chapter describes how to configure outside connections to another network or the
Internet.
7.1 WAN Overview
7.1.1 Nailed-Up Connection (PPP)
A nailed-up connection is a dial-up line where the connection is always up regardless of traffic
demand. The ZyXEL Device does two things when you specify a nailed-up connection. The
first is that the idle timeout is disabled. The second is that the ZyXEL Device automatically
tries to bring up the connection when it is turned on or when the connection is down. Do not
set up a nailed-up connection unless your telephone company offers flat-rate service or you
need a constant connection and the cost is of no concern.
7.1.2 Metric
The metric represents the "cost of transmission". A router determines the best route for
transmission by choosing a path with the lowest "cost". RIP routing uses hop count as the
measurement of cost, with a minimum of "1" for directly connected networks. The number
must be between "1" and "15"; a number greater than "15" means the link is down. The
smaller the number, the lower the "cost".
The metric sets the priority for the ZyXEL Device’s routes to the Internet. If any two of the
default routes have the same metric, the ZyXEL Device uses the following pre-defined
priorities:
• Normal route: designated by the ISP (see Section 7.2 on page 120 )
• Traffic-redirect route (see Section 7.4 on page 124 )
For example, if the normal route has a metric of "1" and the traffic-redirect route has a metric
of "2", then the normal route acts as the primary default route. If the normal route fails to
connect to the Internet, the ZyXEL Device tries the traffic-redirect route next.
If you want the traffic-redirect route to take first priority over the normal route, set the traffic-
redirect’s route metric to "1" and the others to "2" (or greater).
IP Policy Routing overrides the default routing behavior and takes priority over all of the
routes mentioned above.