Technical Reference - ZyXEL Communications NXC5200 User Manual

Chapter 12 Policy and Static Routes

12.4 Technical Reference

The following section contains additional technical information about the features
described in this chapter.
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 73 Assured Forwarding (AF) Behavior Group
Low Drop Precedence
Medium Drop Precedence
High Drop Precedence
208
Class 1 Class 2
AF11 (10) AF21 (18)
AF12 (12) AF22 (20)
AF13 (14) AF23 (22)
Class 3 Class 4
AF31 (26) AF41 (34)
AF32 (28) AF42 (36)
AF33 (30) AF43 (38)
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