Juniper Internet Router M160, Руководство по оборудованию

Страница: 72 / 312

M160 Internet Router Hardware Guide
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, or prevent the route
from being exported altogether. You also can define policies for redistributing
the routes learned from one protocol into another protocol.
VPNs
The JUNOS software supports several types of VPNs:
Layer 2 VPNs—A Layer 2 VPN links a set of sites sharing common routing
information, and whose connectivity is controlled by a collection of policies. A
Layer 2 VPN is not aware of routes within a customer’s network. It simply
provides private links between a customer’s sites over the service provider’s
existing public Internet backbone.
Layer 3 VPNs—A Layer 3 VPN links a set of sites that share common routing
information, and whose connectivity is controlled by a collection of policies.
A Layer 3 VPN is aware of routes within a customer’s network, requiring
more configuration on the part of the service provider than a Layer 2 VPN.
The sites that make up a Layer 3 VPN are connected over a service provider’s
existing public Internet backbone.
Interprovider VPNs—An interprovider VPN supplies connectivity between two
VPNs in separate autonomous systems (ASs). This functionality could be used
48
Routing Engine Software Components