ZyXEL Communications Prestige 643 - Manual (Page 153)

Prestige 643 ADSL Router
IP Policy Routing 12-1
Chapter 12
IP Policy Routing
12.1 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.
12.1.1 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.
12.1.2 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.