This is another difficult section in the blueprint to write about. I find troubleshooting techniques and methodologies to be quite personal; no two people's brains work the same way. I guess this is based on how I do things and some tips I've received from a few people over the years.
1.3.b (i) Diagnose the root cause of networking issue (analyze symptoms, identify and describe root cause)
Read the information in the support ticket very carefully, and take into consideration all of the symptoms. Take particular note of anything that may have changed around the time the symptoms start. This should give you a vague area to begin – L2, L3, specific routing protocol, etc. Verify that the fault is as described. Either start hop by hop, or use split half, to try and isolate the problem.
1.3.b (ii) Design and implement valid solutions according to constraints
Within the guidelines of what is permitted within the scope of the network design (or exam question!), draft a solution. Write it down if needed for clarity. Review this solution in your head before implementing. Think outside the box – is the solution you are proposing going to have any knock on effects to other services? Implement. If it doesn’t work, don’t jump in head first and start changing things. Step back, reassess, and start the process again. Otherwise you end up changing so many things you don’t know what you did.
1.3.b (iii) Verify and monitor resolution
Use the appropriate show commands to verify that everything has worked as expected. Test end to end connectivity.