Final answer:
To troubleshoot a router stuck in the "ExStart" state, you should check neighboring routers, MTU size, and authentication settings.
Step-by-step explanation:
When a router is stuck in the "ExStart" state, there are several things you can check to troubleshoot the issue:
- Neighboring Routers: Ensure that neighboring routers have compatible configurations and are able to establish an adjacency.
- MTU Size: Verify that the Maximum Transmission Unit (MTU) size is the same on both ends of the interface connecting the routers.
- Authentication: Check the authentication settings to make sure they match on both routers.
When a router is stuck in the ExStart state, it suggests an issue with the OSPF (Open Shortest Path First) protocol exchange process. First, check for matching OSPF parameters between the neighbors, including the MTU size, area ID, authentication type, and password.
These parameters must match for the OSPF adjacency to proceed to the next state. Also, verify the network connectivity and inspect the physical layer and data link layer for any potential issues. Sometimes, the problem might be due to faulty cables or interfaces.
Additionally, ensure that there are no access lists blocking OSPF traffic, as the OSPF Hello and Dead intervals need to match between neighbors to form a proper adjacency.