Policy-Based Routing; Overview; Policy-Based Routing Tables; Policy-Based Routing Rules - D-Link DFL-260E User Manual

4.3. Policy-based Routing

4.3. Policy-based Routing

4.3.1. Overview

Policy-based Routing (PBR) is an extension to the standard routing described previously. It offers
administrators significant flexibility in implementing routing decision policies by being able to
define rules so alternative routing tables are used.
Normal routing forwards packets according to destination IP address information derived from static
routes or from a dynamic routing protocol. For example, using OSPF, the route chosen for packets
will be the least-cost (shortest) path derived from an SPF calculation. Policy-based Routing means
that routes chosen for traffic can be based on specific traffic parameters.
Policy-based Routing can allow:
Source based routing
Service-based Routing
User based Routing
Policy-based Routing implementation in NetDefendOS is based on two building blocks:
• One or more user-defined alternate Policy-based Routing Tables in addition to the standard
default main routing table.
• One or more Policy-based routing rules which determines which routing table to use for which
traffic.

4.3.2. Policy-based Routing Tables

NetDefendOS, as standard, has one default routing table called main. In addition to the main table,
it is possible to define one or more, additional alternate routing tables (this section will sometimes
refer to these Policy-based Routing Tables as alternate routing tables).
Alternate routing tables contain the same information for describing routes as main, except that
there is an extra parameter ordering defined for each of them. This parameter decides how route
lookup is done using alternate tables in conjunction with the main table. This is described further in
Section 4.3.5, "The Ordering parameter".

4.3.3. Policy-based Routing Rules

A rule in the policy-based routing rule set can decide which routing table is selected. A Policy-based
Routing rule can be triggered by the type of service (HTTP for example) in combination with the
Source/Destination Interface and Source/Destination Network.
A different routing table may need to be chosen based on the
source of traffic. When more than one ISP is used to provide
Internet services, Policy-based Routing can route traffic
originating from different sets of users through different routes.
For example, traffic from one address range might be routed
through one ISP, whilst traffic from another address range might
be through a second ISP.
A different routing table might need to be chosen based on the
service. Policy-based Routing can route a given protocol such as
HTTP, through proxies such as Web caches. Specific services
might also be routed to a specific ISP so that one ISP handles all
HTTP traffic.
A different routing table might need to be chosen based on the
user identity or the group to which the user belongs. This is
particularly useful in provider-independent metropolitan area
networks where all users share a common active backbone, but
each can use different ISPs, subscribing to different providers.
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Chapter 4. Routing