Technical support interview questions

Hello guys,

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I've some technical questions which were previously asked so I just wanted to check the answers or logic.

I've submitted my answers, please correct me if I am wrong or suggest good alternate solutions.

And I hope these Q&A will prove helpful for someone.

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Really appreciate your time.

Q1: How to check if a port is open or blocked on some server?

Scenario :

You can remotely connect from 192.168.1.2 (your office) to you server 11.21.1.1(some public ip) but you come back home and you want to work remotely. So you try to connect from your home, it is not able to connect. Steps to troubleshoot? So how do you check open / blocking ports on server,   How'd you investigate on server side or on your local network side to mitigate the issue.

Assuming our local private home network is just working fine for other websites and connectivity.

One of the very basic thing is remoting to server. We can do it using SSH which is more secure. So the scenario where I am not able to connect to server in order to work from home. The application that is trying to connect to server port, let’s say 569.

· So yeah in order to check ports on server side, we can SSH to server which of course use different port 22 to see if we can SSH, if that specific port 569 is causing trouble for some reason then we will get to know.

· All time useful command for port troubleshooting, netstat -bano lists all ports with local and foreign Ip address with status [listening, established, time_wait]

· Then we can also trace the route to see if the packet is dropping in our network only? Means we need to check settings from our side like settings on our router and on our personal system and also firewall ports.

· to mitigate the problem down to one I’d say try to connect with that same application from other device within same network, if not, then try to connect to that server app using different network along with different system.

· Checks to do on Server side

1. Again port forwarding is important here as well because if someone from outside is accessing that port, it should be redirected properly.
2. Of course verifying ACL’s on our server

· Checks to do on our network side

1. If this is the first time trying to do work from home, then yes we need to check everything and will take time otherwise some minor problem could have occurred.
2. So we’re going to check if in router settings, port forwarding set up correctly.
3. Windows firewall or router firewall needs to be checked.
4. In port forwarding if the same port is used for 2 different rules will cause problem
5. We can also do log analysis to make decisions with applications like Wireshark on network, Firewall log etc.

Q2: TCP vs UDP which carries more data?

TCP header is 20 bytes while UDP is 8 bytes and then remaining is used for data defined by our MTU. UDP has 60% lesser header than TCP so it will end up carrying more data actually.

Conclusion that 60% there makes a lot of difference with carrying capacity.

Q3: If an application throws an error it cannot write to the disk, what steps would you follow to troubleshoot?( a question related to storage issues). By writing means , could be generating a log or producing any file or anything.\**

So we need to check drive if it is overloaded.

To my knowledge , an application is directed to write to a specific drive within a specific folder ( it is supposed to write somewhere).

Or

Since a corporate system are under a domain so an employee does not have full control for permission settings or even if he executes a script, it can’t change anything. However, assuming user is the admin itself so what we can do is check permission settings if we navigate to drive: to see properties=>security, we will be able to see different permissions set.

So may be the user forgot to execute that application as admin or if he wants the easy way then he can have full control to that user but that is not secure.

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