How is designated router selection in ospf

Then, the DR will update all other routers in the area. If the Designated Router DR not exists, each router would have to update its neighbour.

If the routers are interconnected, this can direct to multiple unnecessary updates. Having a Designated Router DR will assist to eliminate this problem. The number of adjacencies has been reduced to 3, which is 6 adjacencies without a Designated Router DR. If the OSPF enabled router powered on it also start the election process. Now lookit figure 2, all Ethernet router interfaces have a default priority of 1. If the router identifier is modified in a network, the link-state advertisements LSAs advertised by the previous router identifier are retained in the OSPF database until the LSA retransmit interval has timed out.

Hence, it is strongly recommended that you explicitly configure the router identifier under the [edit routing-options] hierarchy level to avoid unpredictable behavior if the interface address on a loopback interface changes.

To quickly configure an OSPF router identifier, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode. Confirm your configuration by entering the show routing-options router-id command.

If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration. The router ID fields are clearly marked in the output. This example shows how to control OSPF designated router election. The higher the priority value, the greater likelihood the routing device will become the designated router.

To quickly configure an OSPF designated router election, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode.

Note: To specify an OSPFv3 interface, include the ospf3 statement at the [edit protocols] hierarchy level. Confirm your configuration by entering the show protocols ospf command. To confirm your OSPFv3 configuration, enter the show protocols ospf3 command.

From operational mode, enter the show ospf interface and the show ospf neighbor commands for OSPFv2, and enter the show ospf3 interface and the show ospf3 neighbor commands for OSPFv3. All rights reserved. Help us improve your experience. Let us know what you think. You can approximate NBMA networks with point-to-point serial interfaces by using a frame relay switch in the middle and having the broadcast command configured in your frame-relay map. Perhaps you have confused NBMA with point-to-point serial interfaces due to the interface type used?

If you connect routers to other routers using a serial link then they're point-to-point networks, not NBMA networks. Would changing the OSPF priority at one of the interface end points of the tunnel result in the adjacency being formed? All, I got it working. It was due to a rogue static route pointing to one of the tunnel interfaces. I made the same mistake as a newbie. I believe what had happened here is that you have two separate segments i.

Since this is the case your router is DR for both of these broadcast domains. What are the timer involved in the background,if any? Can you please explain? This concise and clear look at OSPF neighbors helped me keep this sorted out for a recent certification exam, thanks!

Wonderful article at the same time it is written amazingly simple words that made it very easy to understand at 1st sight. Hi Jeremy, what will happen if we configure the highest priority router at the end?

Is there any way to make the Router is DR even though the priority for this router and the router ID isn't the highest? Have you been looking for a better way to model your network infrastructure? Check out what we're doing with NetBox! Open source and widely extensible, NetBox has enabled thousands of organizations to automate their networks like never before possible. Posted in Routing. Support PacketLife by buying stuff you don't need! Thanks, Paul. Bored AT Work June 3, at p.

OmiPR June 3, at p.