Bgp Overview - Juniper J2300 User Manual

J-series™ Services Router User Guide
Figure 66: OSPF AS Network with Stub Areas and NSSAs
Area 0.0.0.3
To control the advertisement of external routes into an area, OSPF uses stub
areas. By designating an area border router interface to the area as a stub
interface, you suppress external route advertisements through the area border
router. Instead, the area border router automatically advertises a default
route (through itself) in place of the external routes. Packets destined for
external routes are automatically sent to the area border router, which acts as
a gateway for outbound traffic and routes them appropriately.
For example, area
network. All outbound traffic is routed through the area border router to the
backbone and then to the destination addresses. By designating area
stub area, you reduce the size of the topology database for that area by limiting
the route entries to only those routes internal to the area.
Like area
area
can limit the external route advertisements to the area and advertise the static
customer routes by designating it a not-so-stubby area (NSSA). External routes
are flooded into the NSSA and then leaked to the other areas, but external
routes from other areas are not advertised within the NSSA.

BGP Overview

The Border Gateway Protocol (BGP) is an exterior gateway protocol (EGP) used
primarily to establish point-to-point connections and transmit data between peer
ASs. Unlike the IGPs RIP and OSPF, BGP must explicitly advertise the routes
between its peers. The route advertisements determine prefix reachability and the
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BGP Overview
Area 0.0.0.0
in Figure 66 is not directly connected to the outside
0.0.0.3
in Figure 66, area
0.0.0.3
has static customer routes that are not internal OSPF routes. You
0.0.0.4
Static customer routes
192.112.67.14
192.112.67.29
...
Area 0.0.0:4
has no external connections. However,
0.0.0.4
a
0.0.0.3