ZyXEL ISG50-PSTN User Guide - Page 299
Policy Routing Technical Reference
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Chapter 14 Policy and Static Routes Table 89 Configuration > Network > Routing > Static Route > Add (continued) LABEL DESCRIPTION Metric Metric represents the "cost" of transmission for routing purposes. IP routing uses hop count as the measurement of cost, with a minimum of 1 for directly connected networks. Enter a number that approximates the cost for this link. The number need not be precise, but it must be 0~127. In practice, 2 or 3 is usually a good number. OK Click OK to save your changes back to the ISG50. Cancel Click Cancel to exit this screen without saving. 14.4 Policy Routing Technical Reference Here is more detailed information about some of the features you can configure in policy routing. NAT and SNAT NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address in a packet in one network to a different IP address in another network. Use SNAT (Source NAT) to change the source IP address in one network to a different IP address in another network. Assured Forwarding (AF) PHB for DiffServ Assured Forwarding (AF) behavior is defined in RFC 2597. The AF behavior group defines four AF classes. Inside each class, packets are given a high, medium or low drop precedence. The drop precedence determines the probability that routers in the network will drop packets when congestion occurs. If congestion occurs between classes, the traffic in the higher class (smaller numbered class) is generally given priority. Combining the classes and drop precedence produces the following twelve DSCP encodings from AF11 through AF43. The decimal equivalent is listed in brackets. Table 90 Assured Forwarding (AF) Behavior Group CLASS 1 CLASS 2 Low Drop Precedence AF11 (10) AF21 (18) Medium Drop Precedence AF12 (12) AF22 (20) High Drop Precedence AF13 (14) AF23 (22) CLASS 3 AF31 (26) AF32 (28) AF33 (30) CLASS 4 AF41 (34) AF42 (36) AF43 (38) Port Triggering Some services use a dedicated range of ports on the client side and a dedicated range of ports on the server side. With regular port forwarding, you set the port(s) and IP address to forward a service (coming in from the remote server) to a client computer. The problem is that port forwarding only forwards a service to a single IP address. In order to use the same service on a different computer, you have to manually replace the client computer's IP address with another client computer's IP address. Port triggering allows the client computer to take turns using a service dynamically. Whenever a client computer's packets match the routing policy, it can use the pre-defined port triggering setting ISG50 User's Guide 299