Alteon Application Switch Operating System Application Guide
Open Shortest Path First (OSPF)
Document ID: RDWR-ALOS-V2900_AG1302
139
Types of OSPF Routing Devices
Figure 18 - OSPF Routing Device Types, page 139
, 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 18: OSPF Routing Device Types
Neighbors and Adjacencies
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.
