Chapter 15 Ip Policy Routing; Introduction; 15.1.1 Benefits; 15.1.2 Routing Policy - ZyXEL Communications PRESTIGE 1400 User Manual

Prestige 1400 WAN Router with Integrated Ethernet Switch
Chapter 15
IP Policy Routing
This chapter helps you to configure 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 batch 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.
The actions that can be taken include routing the packet to a different gateway (and hence the outgoing interface)
and the TOS and precedence fields in the IP header.
IPPR follows the existing packet filtering facility of ZyNOS in style and in implementation. The policies are
divided into sets, where related policies are grouped together. A user defines the policies before applying them to
an interface or a remote node, in the same fashion as the filters. There are twelve policy sets with six policies in
each set.
15-1 IP Policy Routing