ZyXEL Communications ZyXEL ExpWave 240B - Manual (Page 91)

ExpWave 240B Secure Outdoor Ethernet Radio Link
IP Policy Routing 15-1
Chapter 15 IP Routing Policy Setup
This chapter covers setting and applying policies used for IP routing.
15.1 Introduction
Traditionally, routing is based on the destination address only and the ExpWave 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.
15.2 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.
15.3 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
includes 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.
IPPR follows the existing packet filtering facility of RAS 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 12 policy sets with six policies in each set.
15.4 IP Routing Policy Setup