Influencing DR/BDR Election in OSPF | ospf dr/bdr election
Asalam o alikum, brothers & sisters. Today we will learn influencing DR/BDR Election in OSPF.
Based on the network type, OSPF router can elect one router to be a Designated Router (DR) and one router to be a Backup Designated Router (BDR). For example, on multiaccess broadcast networks (such as LANs) routers defaults to elect a DR and BDR. DR and BDR serve as the central point for exchanging OSPF routing information. Each non-DR or non-BDR router will exchange routing information only with the DR and BDR, instead of exchanging updates with every router on the network segment. DR will then distribute topology information to every other router inside the same area, which greatly reduces OSPF traffic.
DR/BDR Election is a process in OSPF by which OSPF Selects a DR and BDR in its topology. What if we want some other Router to become the in charge (DR) ? This can be achieved by changing the default priority of Router in OSPF.
We change the priority by using the ip ospf priority command:
- The default priority is 1.
- A priority of 0 means that Router will never be elected as DR or BDR.
- Pri of 255 means , it will surely be the DR
- You need to use clear ip ospf process before this change takes effect.
By default, all Routers have a priority of 1. So 2nd factor in deciding the DR is “Router-Id”. The router ID uniquely identifies a router within an OSPF domain. 3 ways to assign a Router-ID are mentioned below:
- Manually configuring Router-ID .
- Highest IP Address on Loopback Interface
- Highest IP Address on non-loopback Interface (any physical Interface)
In our lab scenario we have 3 Routers. R0 , R1 and R2. R0 is elected as the DR for this network , as it has the highest Router-ID “18.104.22.168” , while R1 is the BDR having Router-ID of 22.214.171.124.
Now let’s change the pri of R2 , such that it becomes the DR.
Don’t forget to watch the video tutorial::