Are you familiar with the OSPF DR election process? If not, or if you're just looking for a refresher, read on!
This article will explain what DR elections are, why they happen, and how routers determine who will become the DR.
We'll also discuss some of the factors that can influence the outcome of a DR election.
So whether you're an experienced OSPF user or just getting started, this post has something for you!
Before Moving On: What Is OSPF DR (Designated Router)?
The Open Shortest Path First (OSPF) protocol is used in computer networking to find the shortest path between network nodes. The OSPF protocol uses a link-state algorithm, meaning each node maintains a database of all available routes and their associated costs. When a node wants to find the shortest path to another node, it simply looks up the best route in its database.
Designated Routers (DRs) are essential in OSPF protocol networks. The Designated Router (DR) and a Backup Designated Router (BDR) in OSPF play the role of a central point for exchanging OSPF information between many routers on the same multiaccess broadcast network segment.
Non-DR and non-BDR routers only need to exchange routing information with the DR and BDR rather than every router on the segment. As you can see, DRs play a vital role in ensuring that networks using the OSPF protocol remain operational.
So, How Does OSPF DR Election Work?
As mentioned above, for an Open Shortest Path First (OSPF) router to become a Designated Router (DR), it must first go through an election process.
This process starts when each router on the network sends out a Hello message. The Hello message contains information about the router's identity, priority, and options. The router with the highest priority becomes the DR, while the router with the second highest priority becomes the Backup Designated Router (BDR).
If two routers have the same priority, then the one with the higher router ID becomes the DR. Once the DR and BDR have been elected, they begin exchanging routing information with each other to maintain synchronized copies of the routing table. If the DR fails, then the BDR takes over its responsibilities.
The election process always ensures that a DR and BDR are available to exchange routing information and keep the network running smoothly. We should add that you can configure the DR/BDR selection by manually designating priority to routers.
A Quick Recap of the OSPF DR Election:
- “ip ospf priority” command is used for setting the priority on the router interface.
- The default priority is always 1.
- Priority 0 means that the router will never be selected DR or BDR.
- The “clear ip ospf process” command must be used in order for changes to be effective.
You can find well-prepared documents about OSPF DR and BDR Electionin our CCIE Enterprise Infrastructure Course.
DR elections are a critical part of the OSPF protocol, and it is important to understand why they happen and how they work to troubleshoot any issues.
By understanding the mechanics of the election process, you can help ensure that your network runs smoothly.
Also you can learn more about the OSPF DR election and more at Cisco's OSPF Design Guide here.