In Cisco switches, when OSPF Router Priority is set to a lower value, you may receive the following type of log message:

%OSPF-5-DRCHANGE: Process <Process_ID>, Nbr <Neighbor_IP> on <Interface> from DR to BDR, OSPF Router Priority Lowered

Explanation of the log message:

  • %OSPF-5-DRCHANGE: This log message indicates a change in the OSPF designated router (DR) or backup designated router (BDR).
  • Process <Process_ID>: The log message includes the OSPF process ID for the specific OSPF instance running on the Cisco switch.
  • Nbr <Neighbor_IP>: This part shows the IP address of the OSPF neighbor with whom the designated router or backup designated router status has changed.
  • on <Interface>: The log message specifies the name of the interface where the OSPF adjacency change occurred.
  • from DR to BDR: This section indicates that the router’s OSPF priority was lowered, resulting in a transition from the DR to the BDR role.

The log message serves as a notification to network administrators that the OSPF Router Priority has been lowered, potentially affecting the router’s role as a designated router (DR) or backup designated router (BDR). The designated router and backup designated router play critical roles in OSPF network topology, and a lower OSPF priority might prevent a router from becoming a DR or BDR. This can have implications on OSPF network convergence and routing decisions. Network administrators should be aware of such log messages and verify the OSPF router priority settings to ensure proper OSPF network operation and stability.

Solution:

In OSPF, routers elect designated routers (DRs) and backup designated routers (BDRs) to manage communication within a network segment. However, when a router’s OSPF priority is set to a lower value, it may not become a DR or BDR, potentially affecting network convergence and routing decisions. In this article, we will explore the challenges of OSPF Router Priority issues and provide a step-by-step solution using commands to ensure proper designated router election on Cisco devices.

Understanding OSPF Router Priority: OSPF Router Priority is used to determine the eligibility of a router to become a DR or BDR on a multi-access network segment. The router with the highest priority becomes the DR, and the one with the second-highest priority becomes the BDR. Routers with a lower OSPF priority are excluded from these roles.

Solution for Resolving OSPF Router Priority Issue:

Step 1: Verify OSPF Router Priority: Check the OSPF priority settings on each router within the network. Use the following command on each router:

show ip ospf interface

Step 2: Identify the Routers with Lower Priority: Identify the routers with a lower OSPF priority from the output of the previous command. Make a note of the router interfaces and their corresponding OSPF priorities.

Step 3: Increase OSPF Router Priority: Select the desired OSPF priority for the router that should become a DR or BDR. Use the following command on each router to increase the OSPF priority:

interface <Interface>
ip ospf priority <Desired_Priority>

Replace <Interface> with the name of the router’s interface and <Desired_Priority> with the chosen OSPF priority value.

Step 4: Clear OSPF Process: Clear the OSPF process on each router to apply the changes and allow the router to participate in the designated router election:

clear ip ospf process

Conclusion: Resolving OSPF Router Priority issues is essential for proper DR and BDR election within the network. By following the step-by-step solution provided in this article and using the correct commands on Cisco devices, network administrators can quickly identify and rectify routers with lower OSPF priority. Increasing the OSPF priority on the desired routers ensures their eligibility for becoming DRs or BDRs, facilitating efficient communication and routing decisions. Regular monitoring and proactive management of OSPF priority configurations will contribute to a robust OSPF network infrastructure, enabling optimal network convergence and stability.

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