Policy Routing Technical Reference; Routing Protocols Overview - ZyXEL Communications ZyWall 110 User Manual

11.4 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 141 Assured Forwarding (AF) Behavior Group
Low Drop Precedence
Medium Drop Precedence
High Drop Precedence
Maximize Bandwidth Usage
The maximize bandwidth usage option allows the Zyxel Device to divide up any available bandwidth on
the interface (including unallocated bandwidth and any allocated bandwidth that a policy route is not
using) among the policy routes that require more bandwidth.
When you enable maximize bandwidth usage, the Zyxel Device first makes sure that each policy route
gets up to its bandwidth allotment. Next, the Zyxel Device divides up an interface's available bandwidth
(bandwidth that is unbudgeted or unused by the policy routes) depending on how many policy routes
require more bandwidth and on their priority levels. When only one policy route requires more
bandwidth, the Zyxel Device gives the extra bandwidth to that policy route.
When multiple policy routes require more bandwidth, the Zyxel Device gives the highest priority policy
routes the available bandwidth first (as much as they require, if there is enough available bandwidth),
and then to lower priority policy routes if there is still bandwidth available. The Zyxel Device distributes
the available bandwidth equally among policy routes with the same priority level.

11.5 Routing Protocols Overview

Routing protocols give the Zyxel Device routing information about the network from other routers. The
Zyxel Device stores this routing information in the routing table it uses to make routing decisions. In turn,
the Zyxel Device can also use routing protocols to propagate routing information to other routers.
Chapter 11 Routing
CLASS 1 CLASS 2
AF11 (10) AF21 (18)
AF12 (12) AF22 (20)
AF13 (14) AF23 (22)
ZyWALL USG Series User's Guide
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CLASS 3 CLASS 4
AF31 (26) AF41 (34)
AF32 (28) AF42 (36)
AF33 (30) AF43 (38)