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OSPF Adjacency Stuck in EXSTART on Cisco IOS XR – Issue and Solution

In a recent lab setup using Cisco IOS XR on EVE-NG, I faced a common but frustrating issue with OSPF adjacencies getting stuck in the EXSTART state. After spending considerable time troubleshooting interface MTUs and configurations, I discovered that the root cause was related to the virtual network interface type being used. This post outlines the issue, troubleshooting steps, and the eventual solution that got everything working.

Issue:

While configuring OSPF between two routers running Cisco IOS XR in my lab, OSPF adjacencies were getting stuck in the EXSTART state. I verified that interface configurations, MTU settings, and OSPF parameters were correct, but the problem persisted. I tried adjusting the MTU size, using the mtu-ignore command, and even checked for ACLs, but nothing seemed to resolve the issue.

Troubleshooting Steps:

  1. MTU Settings: I started by verifying that both sides of the OSPF adjacency had matching MTUs. I used the default MTU and even tried different values with mtu-ignore, but the issue remained.

  2. OSPF Configuration: I ensured that the OSPF network type was set to point-to-point and double-checked the OSPF process configurations, but still no luck.

  3. Logs & Debugs: I ran debug ip ospf to trace the OSPF process, which consistently showed that the neighbor was stuck in EXSTART due to DBD retransmissions.

  4. Interface Type: Finally, I looked into the type of virtual network interface being used in the EVE-NG topology. By default, the interfaces were set to virtio-net-pc, which I suspected could be causing some compatibility issues with Cisco IOS XR.

Solution:

After several hours of troubleshooting, the breakthrough came from changing the interface type in EVE-NG. I switched the interfaces from virtio-net-pc to e1000, which is widely supported and stable. Once the change was made, the OSPF adjacency came up immediately, and everything worked as expected.

Conclusion:

This issue highlights the importance of considering all aspects of virtual environments, including the type of interfaces in use. If you're using Cisco IOS XR in EVE-NG and facing similar OSPF adjacency issues, make sure to check the interface type and switch to e1000. This simple change saved me a lot of time and solved the problem instantly.

Key Takeaway: Always consider the interface type when working with virtual labs in EVE-NG, especially with Cisco IOS XR. It might save you hours of troubleshooting!

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