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The DR solves the two problems by representing the multiaccess network as a single “virtual router” or “pseudo-node” to the rest of the network and managing the process of flooding link-state advertisements on the multiaccess network. To address these issues, multiaccess networks such as LANs always elect a designated router for OSPF. Flooding over a LAN with many OSPF routers is chaotic, as link-state advertisements are flooded and “reflooded” on the LAN.
![router on a stick ospf required router on a stick ospf required](https://itexamanswers.net/wp-content/uploads/2017/09/98.png)
Second, and just as bad, is the need for flooding. A simple LAN with five OSPF routers would need N ( N − 1)/2, or 5(4)/2=20 link-state advertisements just to represent the links between the routers, even though all five routers are mutually adjacent on the LAN and any frame sent by one is received by the other four.
![router on a stick ospf required router on a stick ospf required](https://media.geeksforgeeks.org/wp-content/uploads/rrf.png)
First is the fact that the link-state database represents links and routers as a directed graph. There are two major problems with LANs and public data networks like ATM and frame relay (called non-broadcast multiple-access, or NBMA, networks). These have nothing to do with ABRs and ASBRs, and concern only the relationship between OSPF routers on links that deliver packets to more than one destination at the same time (mainly LANs). Walter Goralski, in The Illustrated Network (Second Edition), 2017 OSPF Designated Router and Backup Designated RouterĪn OSPF router can also be a Designated Router (DR) and Backup Designated Router (BDR).