ZyXEL Communications P-660HW-T - V2, Руководство пользователя

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P-660HW-T v2 User’s Guide
78 Chapter 5 WAN Setup
5.1.5.3 IP Assignment with ENET ENCAP Encapsulation
In this case you can have either a static or dynamic IP. For a static IP you must fill in all the IP
Address and ENET ENCAP Gateway fields as supplied by your ISP. However for a
dynamic IP, the ZyXEL Device acts as a DHCP client on the WAN port and so the IP
Address and ENET ENCAP Gateway fields are not applicable (N/A) as the DHCP server
assigns them to the ZyXEL Device.
5.1.6 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 idle timeout is disabled. The second is that the ZyXEL Device will try to bring up
the connection when turned on and whenever the connection is down. A nailed-up connection
can be very expensive for obvious reasons.
Do not specify 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
5.1.7 NAT
NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a
host in a packet, for example, the source address of an outgoing packet, used within one
network to a different IP address known within another network.
5.2 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 5.5 on page 81 )
• Traffic-redirect route (see Section 5.7 on page 89 )
• WAN-backup route, also called dial-backup (see Section 5.8 on page 90 )
For example, if the normal route has a metric of "1" and the traffic-redirect route has a metric
of "2" and dial-backup route has a metric of "3", 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. In the same manner, the ZyXEL Device uses the dial-backup route
if the traffic-redirect route also fails.