ZyXEL ADSL2+ User Manual download pdf (Page 229)

Prestige 660RU-Tx Series User’s Guide

Chapter 28 IP Policy Routing 228

CHAPTER 28

IP Policy Routing

This chapter covers setting and applying policies used for IP routing.

28.1 IP Policy Routing Overview

Traditionally, routing is based on the destination address only and the IAD takes the shortest

path to forward a packet. IP Routing Policy (IPPR) provides a mechanism to override the

default routing behavior and alter the packet forwarding based on the policy defined by the

network administrator. Policy-based routing is applied to incoming packets on a per interface

basis, prior to the normal routing.

28.2 Benefits of IP Policy Routing

Source-Based Routing – Network administrators can use policy-based routing to direct traffic

from different users through different connections.

Quality of Service (QoS) – Organizations can differentiate traffic by setting the precedence or

TOS (Type of Service) values in the IP header at the periphery of the network to enable the

backbone to prioritize traffic.

Cost Savings – IPPR allows organizations to distribute interactive traffic on high-bandwidth,

high-cost paths while using low-cost paths for batch traffic.

Load Sharing – Network administrators can use IPPR to distribute traffic among multiple

paths.

28.3 Routing Policy

Individual routing policies are used as part of the overall IPPR process. A policy defines the

matching criteria and the action to take when a packet meets the criteria. The action is taken

only when all the criteria are met. The criteria includes the source address and port, IP protocol

(ICMP, UDP, TCP, etc.), destination address and port, TOS and precedence (fields in the IP

header) and length. The inclusion of length criterion is to differentiate between interactive and

bulk traffic. Interactive applications, for example, telnet, tend to have short packets, while bulk

traffic, for example, file transfer, tends to have large packets.

The actions that can be taken include:

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ZyXEL ADSL2+ User Manual Page 229