Routing Policy - Juniper TX MATRIX Hardware Manual

TX Matrix Hardware Guide
152
In the unicast routing table, the routing protocol process designates routes with the
lowest preference values as active. By default, a route's preference value is simply a
function of how the routing protocol process learned about the route. You can modify
the default preference value by setting routing policies and configuring other software
parameters. See "Routing Policy" on page 152.
Multicast routing table (cache)—Stores routing information for all multicast protocols
running on the router, including DVMRP and PIM. You can configure additional routes
for inclusion in the routing table.
In the multicast routing table, the routing protocol process uses traffic flow and other
parameters specified by the multicast routing protocol algorithms to select active
routes. The routing protocol process then installs one or more active routes to each
network destination into the TX Matrix Routing Engine's forwarding table.
MPLS routing table—Stores MPLS label information.
You can configure additional routing tables to meet your requirements, as described in
the Junos OS Routing Protocols Configuration Guide.

Routing Policy

By default, all routing protocols place their routes into the routing table. When advertising
routes, the routing protocols, by default, advertise only a limited set of routes from the
routing table. Specifically, each routing protocol exports only the active routes that were
learned by that protocol. In addition, IGPs (IS-IS, OSPF, and RIP) export the direct
(interface) routes for the interfaces on which the protocol is explicitly configured.
For each routing table, you can affect the routes that a protocol places into the table
and the routes from the table that the protocol advertises by defining one or more routing
policies and then applying them to the specific routing protocol.
Routing policies applied when the routing protocol places routes into the routing table
are called import policies because the routes are being imported into the routing table.
Policies applied when the routing protocol is advertising routes that are in the routing
table are called export policies because the routes are being exported from the routing
table. In other words, the terms import and export are used with respect to the routing
table.
Routing policy enables you to control (filter) which routes are imported into the routing
table and which routes are exported from the routing table. Routing policy also allows
you to set the information associated with a route as it is being imported into or exported
from the routing table. Routing policies applied to imported routes control the routes
used to determine active routes, whereas policies applied to exported routes control
which routes a protocol advertises to its neighbors.
You implement routing policy by defining policies. A policy specifies the conditions to
use to match a route and the action to perform on the route when a match occurs. For
example, when a routing table imports routing information from a routing protocol, a
routing policy might modify the route's preference, mark the route with a color to identify
it for later manipulation, or prevent the route from even being installed in a routing table.
When a routing table exports routes to a routing protocol, a policy might assign metric
values, modify the BGP community information, tag the route with additional information,
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