Intrvw: Difference between revisions
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;Telephonic Screening
DHCP, '''which packets are unicast, why?'''
3-way Handshake parameters exchanged
How Traceroute works
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How certificates verify URL? Can it be Tempered?
What is SACK
What parameters change in a packet when crossing a Router? '''Does it recalculate Checksums?'''
;2nd 3rd Round
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How Virtual Network Works?
Difference between Bridge & Switch?
'''Example of L4 Service in Netscaler?'''
How does a HTTP Request looks like?
Explain a case you worked recently
How Content Switching Works?
'''Python script logic to find duplicates in list(using arrays)'''
x = [1,2,4,6,8,2,0,3,4,1,9]
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DNS ALG Working
DNS Doctoring, DNS across NAT
Does DNS use TCP or UDP? '''Who decides it?'''
Active vs Passive FTP, ALG working
3-way Handshake
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What is Window Scaling Factor?
How to calculate MTU?
'''What is HTTP Option Connect used for?'''
What is use of SACK?
OSPF States? '''How is Master Elected(Highest Router ID becomes Master)? At which Stage?'''
What is 2 Way State?
Is OSPF Reliable protocol?
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What ICMP Message is sent when Packet is dropped due to larger packet than MTU with DF set?
Can MTU be larger than 1500?
'''What is Elastic IP address?'''
;4th Round
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What is DNS Iterative & Recursive Query?
OSPF: what parameters need to be matching in hello?
'''Does Stub Flags need to be matched?'''
What can be the issue if it gets stuck at Init state?
What can be the issue if it gets stuck at Exstart state? MTU Mismatch.
Scenario based Internet is not reachable in depth Troubleshooting for: [PC]----[Router]----[Internet]
How Traceroute works? Which protocol it uses? (ICMP & UDP)
'''SSL handshake? when Server cert or Client cert asked?'''
What does certificate looks like? What fields are there?
'''How are SSL Keys Calculated?'''
How Virtualization works? XenServer? What is Hypervisor?
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How to find out a session among 224K users, when customer dont know IP address? (Can use Curl custom User Agent & Filter it in traces)
Difference bw HTTP 1.0 & 1.1
'''How to TS Latency in wireshark? Enable Timestamp - Preference > Protocol > TCP > Calc TS.'''
'''How does HTTP Request look like? Which fields are mandatory?'''
'''What is the importance of Host Header? (used when server is having multiple virtual hosts bound to same IP address, used to send request to correct vhost)'''
How to configure Apache Server? What are the various directives? What is root directory?
'''How does HTTPS figure out the correct Server certificate to be sent if multiple vHosts bound to same IP address? At what stage in SSL?'''
▲ There is an TLS Extension called SNI, used to MAP correct Server Name to Certificate.
▲ Sent in Client Hello?? [Need to verify]
Linux Knowledge? Explain any case resolved with that?
App is not accessible in below scenario, How to troubleshoot:
▲ [PC]-----[Router]-----[Server]
▲ IPtables, CPU, Memory, HDD, etc
▲ LSOF, open file limit in old Unix very less ~256, need to extend it, in linux Socket is same as files, so server stop responding after 256 limit.
LB 2 commomnly used methods (Source IP & Cookie Insert), How they work?
'''Which one is more scalable/Efficient?'''
▲ Stateless Session Persistence: Cookie inserted by ADC is more efficient because no need to create a table, NS will insert cookie & forget, with reply, it will read cookie value, decrypt it & fwd request.
▲ State-full Session Persistence: Server will insert cookie, NS will hash it & fwd based on Hash value but will need to keep a table in memory with all hashes & IP Addresses.
▲ Same is true for Source IP based Persistence, Also inefficient behind NAT
▲ Using Set-cookie-header = by Server - insert Name & Value Fields
▲ Client sends cookie in Cookie Header
▲ Who ever generates cookie, will be able to read it
Explain Repro efforts you have done in details.
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