working of dns and its working?

what is a switch, what is a router, how stp works, vlans> difference between tagged & untagged vlan, what steps to use if the switch wents down, DHCP "DORA" process, basic DNS questions. Scenario based questions where a router is placed in between 2 switches in different subnet masks, difference between the Bug Priorities, any Sev 2 bug that you have raised. In Programming part, they asked to write programs to find the multiples of 3 from a given list using list comprehensions, Regular expressions to find the email address from a given file, difference between python 2 & 3, reverse a string

1. What is DHCP, why do we call it works at Layer 7 2. About Wireshark Application, how do we filter the captured packets with protocols 3. What is DNS & its purpose 4. How do we configure DHCP servers and clients and how IP addresses are assigning to them. 5. Where will the username/password of SSH root users be stored. 6. TCP/UDP differences