HP 3500YL - Manual (Page 222)

IP Routing Features
Configuring OSPF
Figure 5-19. Example of Deploying ABRs To Connect Areas to the Backbone
R1
R2 R5
R3
R4 R6
Area 0 (Backbone)
Area 1
Ar
ea
2
Area Border Router (ABR)
Area Border Router
(ABR)
Autonomous System Boundary Router (ASBR)
This type of OSPF router runs multiple Interior Gateway protocols and serves
as a gateway to other autonomous systems operating with interior gateway
protocols. The ASBR imports and translates different protocol routes into
OSPF through redistribution. ASBRs can be used in backbone areas, normal
areas, and NSSAs, but not in stub areas.For more details on redistribution and
configuration examples, see “2. Enable Route Redistribution” on page 5-74.
Designated Routers
In an OSPF network having two or more routers, one router is elected to serve
as the designated router (DR) and another router to act as the backup
designated router (BDR). All other routers in the area forward their routing
information to the DR and BDR, and the DR forwards this information to all
of the routers in the network. This minimizes the amount of repetitive infor­
mation that is forwarded on the network by eliminating the need for each
individual router in the area to forward its routing information to all other
routers in the network. If the area includes multiple networks, then each
network elects its own DR and BDR.
In an OSPF network with no designated router and no backup designated
router, the neighboring router with the highest priority is elected as the DR,
and the router with the next highest priority is elected as the BDR. If the DR
goes off-line, the BDR automatically becomes the DR, and the router with the
next highest priority then becomes the new BDR. If multiple ProCurve routing
switches on the same OSPF network are declaring themselves as DRs, then
both priority and router ID are used to select the designated router and backup
designated routers.
5-48