ZyXEL 4-port Prestige 792H Router 91-004-342001 Manual Do Utilizador

Prestige 791R G.SHDSL Router 

IP Policy Routing 

 

33-1 

Traditionally, routing is based on the destination address only and the IAD takes the shortest path to 
forward a packet. IP Routing Policy (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. 

•  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. 

 

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, for example, telnet, tend to 
have short packets, while bulk traffic, for example, 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.