Handbook

N8406-023 1Gb Intelligent L3 Switch Application Guide 109
OSPF
The switch supports the Open Shortest Path First (OSPF) routing protocol. The switch implementation conforms to
the OSPF version 2 specifications detailed in Internet RFC 1583. The following sections discuss OSPF support for
the switch:
OSPF Overview: This section provides information on OSPF concepts, such as types of OSPF areas, types of
routing devices, neighbors, adjacencies, link state database, authentication, and internal versus external
routing.
OSPF Implementation in the switch. This section describes how OSPF is implemented in the switch, such as
configuration parameters, electing the designated router, summarizing routes, defining route maps and so
forth.
OSPF Configuration Examples. This section provides step-by-step instructions on configuring different
configuration examples:
Creating a simple OSPF domain
Creating virtual links
Summarizing routes
OSPF overview
OSPF is designed for routing traffic within a single IP domain called an Autonomous System (AS). The AS can be
divided into smaller logical units known as areas.
All routing devices maintain link information in their own Link State Database (LSDB). The LSDB for all routing
devices within an area is identical but is not exchanged between different areas. Only routing updates are
exchanged between areas, thereby significantly reducing the overhead for maintaining routing information on a
large, dynamic network.
The following sections describe key OSPF concepts.
Types of OSPF areas
An AS can be broken into logical units known as areas. In any AS with multiple areas, one area must be designated
as area 0, known as the backbone. The backbone acts as the central OSPF area. All other areas in the AS must be
connected to the backbone. Areas inject summary routing information into the backbone, which then distributes it to
other areas as needed.
OSPF defines the following types of areas:
Stub Area—an area that is connected to only one other area. External route information is not distributed into
stub areas.
Not-So-Stubby-Area (NSSA)—similar to a stub area with additional capabilities. External routes from outside
the AS can be advertised within the NSSA but are not distributed into other areas.
Transit Area—an area that allows area summary information to be exchanged between routing devices. The
backbone (area 0), any area that contains a virtual link to connect two areas, and any area that is not a stub
area or an NSSA are considered transit areas