Introduction: Why OSPF Router Priority Matters
In Open Shortest Path First (OSPF) networks, router priority plays a crucial role in Designated Router (DR) and Backup Designated Router (BDR) elections. For Cisco Certifications candidates, understanding this concept is essential—not just for the 200-301 Exam Questions, but for real-world network design and troubleshooting.
Study4Pass breaks down complex networking topics into easy-to-understand lessons. In this guide, you’ll learn:
✔ What OSPF router priority is
✔ The default priority value for Cisco routers
✔ How to configure and verify it
✔ Why this is critical for the CCNA exam
Let’s dive in!
OSPF Router Priority Basics
What Is OSPF Router Priority?
- A numeric value (0-255) that influences DR/BDR elections in multi-access networks (like Ethernet).
- Helps determine which router becomes the DR (primary traffic handler) and BDR (backup).
Why Does It Matter?
- The DR/BDR reduce OSPF traffic overhead by managing Link-State Advertisement (LSA) flooding.
- Without proper priority settings, suboptimal routers might become DR/BDR, hurting performance.
Default Router Priority Value
What’s the Default Priority?
- The default OSPF router priority for all Cisco routers is 1.
What Does a Priority of 0 Mean?
- A router with priority 0 will never participate in DR/BDR elections.
- Useful for routers that should never become DR/BDR (e.g., low-end devices).
Configuring and Verifying OSPF Priority
How to Set OSPF Priority?
- Router(config)# interface GigabitEthernet0/1
- Router(config-if)# ip ospf priority 100
(Sets priority to 100 on the interface)
How to Verify Priority?
- Router# show ip ospf interface GigabitEthernet0/1
(Look for "Router Priority" in the output)
Key Notes:
- Priority is per-interface, not per-router.
- The highest priority becomes DR, second-highest becomes BDR.
- If priorities are equal, the highest Router ID breaks the tie.
Why This Matters for the CCNA Exam
The Cisco CCNA 200-301 exam tests your ability to:
✔ Configure OSPF correctly
✔ Troubleshoot DR/BDR election issues
✔ Interpret show command outputs
Exam Scenarios:
"Why is RouterX not becoming DR even with high priority?"
- Check if OSPF is enabled on the interface.
"How to prevent a router from being DR/BDR?"
- Set priority to 0.
Real-World Implications
When to Adjust Priority?
- Favor high-performance routers as DR (e.g., core switches).
- Avoid making WAN routers DR (they handle less local traffic).
What Happens If DR Fails?
- The BDR takes over, and a new BDR election occurs.
Common Myths About OSPF Priority
Myth: "Higher priority always wins DR election."
✔ Reality: Elections only occur when the current DR/BDR fails—not just because a higher-priority router joins.
Myth: "Priority affects OSPF path selection."
✔ Reality: Priority only influences DR/BDR elections, not SPF calculations.
Myth: "All interfaces on a router must have the same priority."
✔ Reality: Priority is set per interface.
Practice Questions
1. What happens if all routers have the same priority?
- The highest Router ID wins DR election.
2. How do you force a router to never become DR?
- Set its priority to 0.
Bottom Line
Understanding OSPF router priority is critical for:
✔ Passing the CCNA 200-301 exam
✔ Optimizing real-world OSPF networks
✔ Troubleshooting DR/BDR issues
At Study4Pass, we help you simplify complex topics and ace your certification exams.
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Sample Questions for Cisco CCNA 200-301 Certification Exam
What is the default router priority value for all Cisco OSPF routers?
A) 0
B) 1
C) 100
D) 255