Types Of Ospf Routing Devices; Neighbors And Adjacencies - Lenovo Flex System Fabric CN4093 Application Manual

Types of OSPF Routing Devices

BGP
External
Routes
RIP

Neighbors and Adjacencies

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CN4093 Application Guide for N/OS 8.2
As shown in Figure 47, OSPF uses the following types of routing devices:
 Internal Router (IR)—a router that has all of its interfaces within the same area.
IRs maintain LSDBs identical to those of other routing devices within the local
area.
 Area Border Router (ABR)—a router that has interfaces in multiple areas. ABRs
maintain one LSDB for each connected area and disseminate routing
information between areas.
Autonomous System Boundary Router (ASBR)—a router that acts as a gateway

between the OSPF domain and non‐OSPF domains, such as RIP, BGP, and static
routes.
Figure 47. OSPF Domain and an Autonomous System
OSPF Autonomous System
ASBR
ABR
ASBR
Area 1
In areas with two or more routing devices, neighbors and adjacencies are formed.
Neighbors are routing devices that maintain information about each others' health.
To establish neighbor relationships, routing devices periodically send hello packets
on each of their interfaces. All routing devices that share a common network
segment, appear in the same area, and have the same health parameters (hello
and dead intervals) and authentication parameters respond to each other's hello
packets and become neighbors. Neighbors continue to send periodic hello packets
to advertise their health to neighbors. In turn, they listen to hello packets to
determine the health of their neighbors and to establish contact with new
neighbors.
The hello process is used for electing one of the neighbors as the area's Designated
Router (DR) and one as the area's Backup Designated Router (BDR). The DR is
adjacent to all other neighbors and acts as the central contact for database
exchanges. Each neighbor sends its database information to the DR, which relays
the information to the other neighbors.
Backbone
Area 0
Inter-Area Routes
(Summary Routes)
ABR
Area 2
Area 3
ABR
Internal
Router