Manualshelf

Reference Guide

ManualsBrandsDell ManualsAccess PlatformsPowerSwitch S4148F-ON/S4148T-ON/S4148FE-ON
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Table Of Contents
Backbone router A backbone router (BR) is part of the OSPF Backbone, Area 0, and includes all ABRs. The BR includes
routers connected only to the backbone and another ABR, but are only part of Area 0—shown as Router I
in the example.
Area border
router
Within an AS, an area border router (ABR) connects one or more areas to the backbone. The ABR keeps
a copy of the link-state database for every area it connects to. It may keep multiple copies of the link
state database. An ABR summarizes learned information from one of its attached areas before it is sent to
other connected areas. An ABR can connect to many areas in an AS and is considered a member of each
area it connects to—shown as Router H in the example.
Autonomous
system border
router
The autonomous system border router (ASBR) connects to more than one AS and exchanges information
with the routers in other ASs. The ASBR connects to a non-IGP such as BGP or uses static routes—
shown as Router N in the example.
Internal router The internal router (IR) has adjacencies with ONLY routers in the same area—shown as Routers E, F, I, K,
and M in the example.
Designated and backup designated routers
OSPF elects a designated router (DR) and a backup designated router (BDR). The DR is responsible for generating LSAs for the
entire multiaccess network. Designated routers allow a reduction in network traffic and in the size of the topological database.
Designated
router
Maintains a complete topology table of the network and sends updates to the other routers via multicast.
All routers in an area form a slave/master relationship with the DR. Every time a router sends an update,
the router sends it to the DR and BDR. The DR sends the update out to all other routers in the area.
Backup
designated
router
Router that takes over if the DR fails.
Each router exchanges information with the DR and BDR. The DR and BDR relay information to other routers. On broadcast
network segments, the number of OSPF packets reduces by the DR sending OSPF updates to a multicast IP address that all
OSPF routers on the network segment are listening on.
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