Troubleshooting Qs

0) Describe what happens when user tries to open web page in his browser? Assume all caches on host are empty.

1) How traceroute works? Why we may have different results on Win/Linux stations?

2) We don’t have connectivity to server on certain UDP port. How would you troubleshoot this issue (let’s say ICMP is allowed on our network)? What could be wrong on the server itself (assume it’s Linux host)? How to check open ports? How to check if anything is blocking traffic? How to check if packets are reaching server in the first place?

3) Imagine we have encrypted TLS connection from browser to server. How can we get access to clear text to troubleshoot it? (Wireshark session keys dump, server’s private key, TLS full vs abbreviated handshake).

4) Imagine we don’t have connectivity via IPSec VPN tunnel, or it’s slow. Without tunnel connectivity is fine.
What are the most likely reasons? How to diagnose it? What setting can we leverage to prevent issue from happening? (MTU, TCP MSS, MSS clamping)

5) OSPF neighbors won’t come up. How would you troubleshoot the issue?

6) How can you tell wether application is not responding in a timely manner or network is slow?

7) What TCP fast retransmission is? How does it look like in trace files? Why you might see it?
    What is TCP zero window? Why it might happen?

8) How will you troubleshoot the issue when some elements of web page are not loading properly? Which tools you’re going to use for this?

9) Describe probable reasons BGP isn’t installing a route into RIB.

10) Imagine you would like to capture packets on Cisco switch/router, what are possible options?