What is the physical difference between single-mode and multi-mode fibre cables? What is 3-way handshakes? What is the OSI 7-layer? Can you briefly explain? What will you do first when the fibre link down in 2-end? What possible reason do you think when devices cannot communicate with each other within the same switch? What factors will affect the router to choose the best path in BGP? Have you heard about power meter and OTDR? What is DWDM? What is the purpose of port channel? What is the concern? What is the difference between IGP and EGP? Why the neighbour relationship cannot bring up in OSPF? Why OSPF will not elect DR/BDR in a point-to-point connection? What is the key factor if Area 20 need to run OSPF? What would you do if Area 30 is not connect to the backbone area?

TCP vs UDP How does BGP work, and how would you troubleshoot route flapping