Root: WRM Database > Information Technology > Certifications > CCNA
> Routing Protocols
> Designated Router (DR)
> DRs On LANs
The DR concept prevents overloading a subnet with too much OSPF traffic when many routers are on a subnet. Of course, lots of routers could be attached to one LAN, which is why a DR is required for routers attached to a LAN.
Odom, Wendell (2008) CCNA ICND2 Official Exam Certification Guide, Second Edition. Indianapolis: Cisco Press.