Introduction To Ip Unicast Policy Routing; Configuring Ip Unicast Policy Routing; Defining A Policy - 3Com MSR 50 Series Configuration Manual

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Introduction to IP
Unicast Policy Routing
Configuring IP Unicast
Policy Routing

Defining a Policy

IP U
NICAST
C
ONFIGURATION
When configuring IP unicast policy routing, go to these sections for information
you are interested in:
"Introduction to IP Unicast Policy Routing" on page 639
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"IP Unicast Policy Routing Configuration" on page 639
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"Displaying and Maintaining IP Unicast Policy Routing Configuration" on page
■
642
"IP Unicast Policy Routing Configuration Examples" on page 643
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Policy routing (also known as policy based routing) is a routing mechanism based
on the user-defined policies. Different from the traditional destination-based
routing mechanism, policy routing enables you to implement policies (based on
the source address, address length, and other criteria) that make packets flexibly
take different paths.
Policy routing involves system policy routing and interface policy routing:
System policy routing applies to locally generated packets, instead of
■
forwarded packets.
Interface policy routing applies to forwarded packets (arriving on an interface),
■
instead of locally generated packets (for example, ping packets).
As a rule, policy routing takes precedence over destination-based routing. That is,
policy routing is applied when packets match a policy, and otherwise,
destination-based routing is applied. However, if a default outgoing interface (next
hop) is configured, the destination-based routing takes precedence over policy
routing.
A policy can consist of multiple nodes identified by node numbers. The smaller the
node number is, the higher the priority of the node's policy is. A policy, which
consists of if-match clauses and apply clauses, is used to import a route to
forward IP packets.
An if-match clause specifies a matching rule on a node while an apply clause
specifies an action to be taken for packets.
P R
OLICY OUTING