Ip Policy Routing; Introduction; Benefits; Routing Policy - ZyXEL Communications Prestige 480 User Manual

Prestige 480 Dual BRI ISDN Router

15.1 Introduction

Traditionally, routing is based on the destination address only and the router takes the shortest path to
forward a packet. IP Policy Routing (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.

15.1.1 Benefits

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

15.1.2 Routing Policy

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 include 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,
e.g., telnet, tend to have short packets, while bulk traffic, e.g., file transfer, tends to have large packets.

IP Policy Routing

Chapter 15
IP Policy Routing
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