Chapter 18 Policy Route; Introduction To Ip Policy Routing; Benefits; Routing Policy - ZyXEL Communications ZyWall 35 User Manual

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

18.1 Introduction to IP Policy Routing

Traditionally, routing is based on the destination address only and the ZyWALL 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.

18.2 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.

18.3 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 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).
• Setting the ToS and precedence fields in the IP header.

Chapter 18 Policy Route

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