Policy Framework Configuration Guide - Juniper Networks

Chapter 4: Routing Policy Configuration
You can reference the same routing policy one or more times in the same or a different
export statement.
For information about how the policy framework software evaluates a routing policy, see
“How a Routing Policy Is Evaluated” on page 29.
You can apply export policies to routes being exported from the routing table into the
forwarding table for the following features:
• Per-packet load balancing
• Class of service (CoS)
Configuring Dynamic Routing Policies
For more information about per-packet load balancing, see “Configuring Per-Packet
Load Balancing” on page 143. For more information about CoS, see the Junos OS Class of
Service Configuration Guide.
The verification process required to commit configuration changes can entail a significant
amount of overhead and time. For example, changing a prefix in one line of a routing
policy that is 20,000 lines long can take up to 20 seconds to commit. It can be useful to
be able to commit routing policy changes much more quickly.
In Junos OS Release 9.5 and later, you can configure routing policies and certain routing
policy objects in a dynamic database that is not subject to the same verification required
in the standard configuration database. As a result, the time it takes to commit changes
to the dynamic database is much shorter than for the standard configuration database.
You can then reference these policies and policy objects in routing policies you configure
in the standard database. BGP is the only protocol to which you can apply routing policies
that reference policies and policy objects configured in the dynamic database. After you
configure and commit a routing policy based on the objects configured in the dynamic
database, you can quickly update any existing routing policy by making changes to the
dynamic database configuration.
CAUTION: Because the Junos OS does not validate configuration changes
to the dynamic database, when you use this feature, you should test and
verify all configuration changes before committing them.
This section discusses the following topics:
• Configuring Routing Policies and Policy Objects in the Dynamic Database on page 66
• Configuring Routing Policies Based on Dynamic Database Configuration on page 66
• Applying Dynamic Routing Policies to BGP on page 68
• Preventing Reestablishment of BGP Peering Sessions After NSR Routing Engine
Switchover on page 68
• Example: Configuring a BGP Export Policy That References a Dynamic Routing
Policy on page 69
Copyright © 2010, Juniper Networks, Inc.
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