Technical Reference - ZyXEL Communications NXC2500 User Manual

9.4 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 63 Assured Forwarding (AF) Behavior Group
Low Drop Precedence
Medium Drop Precedence
High Drop Precedence
NXC2500 User's Guide
Class 1 Class 2
AF11 (10) AF21 (18)
AF12 (12) AF22 (20)
AF13 (14) AF23 (22)
Chapter 9 Policy and Static Routes
Class 3 Class 4
AF31 (26) AF41 (34)
AF32 (28) AF42 (36)
AF33 (30) AF43 (38)
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