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ThinkMo EDU Share – network 168.General Election Rules for DR/BDR in Networking

ThinkMo No Comments 06/30/2023

ThinkMo EDU Share – network 168.General Election Rules for DR/BDR in Networking

In networking, the selection of Designated Router (DR) and Backup Designated Router (BDR) is crucial for efficient communication within a multi-access network, particularly in protocols such as OSPF (Open Shortest Path First) and IS-IS (Intermediate System to Intermediate System). This article discusses the general election rules that govern the selection process of DR and BDR in such protocols.

DR/BDR Election Process:
The election of DR and BDR follows a specific set of rules to ensure a stable and reliable network. The process typically involves the following steps:

Network Initialization:
When a router joins a multi-access network, it starts in the “Down” state. The router then goes through a series of state transitions, including “Init” and “2-Way” states, before reaching the “DR” or “BDR” state.

Hello Packet Exchange:
Routers exchange Hello packets periodically to establish and maintain neighbor relationships. The Hello packets contain information such as router ID, network mask, and priority value.

Priority-Based Election:
The DR and BDR election is based on priority values assigned to each router. The priority is an integer value ranging from 0 to 255, with higher values indicating a higher priority. By default, the priority is set to 1. However, administrators can manually configure a higher priority for a router to influence the election process.

Router ID Tiebreaker:
In case two routers have the same priority value, the tiebreaker mechanism comes into play. The router with the highest Router ID (RID) becomes the DR, and the second highest RID becomes the BDR. The RID is typically determined based on the highest IP address assigned to a loopback interface or a physical interface.

DR/BDR Functionality:
The elected DR assumes responsibility for maintaining the topology and routing information for the network and acts as the designated intermediary for communication with other routers. The BDR serves as a backup to the DR and takes over its role if the DR fails.

Neighbor Adjacency:
Routers establish neighbor adjacency with the DR and BDR to exchange routing updates efficiently. The DR and BDR update their routing tables based on information received from neighboring routers.

The election of DR and BDR in multi-access networks plays a crucial role in maintaining a stable and efficient routing environment. By following a set of general election rules, such as priority-based selection and Router ID tiebreaker, protocols like OSPF and IS-IS ensure that the most suitable routers assume the roles of DR and BDR. Understanding these rules is essential for network administrators and engineers working with such protocols to design and manage robust and scalable networks.

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