ZyXEL Communications 480 manual Chapter IP Policy Routing, Introduction, Benefits, Routing Policy

Prestige 480 Dual BRI ISDN Router

Chapter 15

IP Policy Routing

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.

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