Interview FAQ's I faced

Interview questions from Cisco, Brocade, Juniper, Broadcom, Aricent, HCL.

Company : Cisco (interview : 5 hrs)
1. Program for String reversal in best efficient way.
2. Program for reversal of n characters in a string. Say string is "interview", your o/p should be "tinvrewei". Reversing for every 3 characters.
3. Basic working of Switch.
4. Use of PVID.
5. Ingress filtering use.
6. ACL's and their use. What is TCAM.
7. Difference between process and threads.
8. How a thread is a light weight process.
9. Difference between binary and counting semaphores. How binary sem is different from mutex.
10. Difference between SNMP V1, V2,V3 protocols.
11. What is Gauge used for. DIfference between Gauge and Counter.
12. Explain what happens when www.yahoo.com is entered in the browser. All the communication that happens. How will the data be retrieved. What happens if the DNS server is connected to a different network.
13. Compose the datastructure that is used in SNMP while searching for a particular OID. Explain the entire search process done to ascertain the OID.
14. give examples for RTOS applications. Where and why they are preferred. How the latency is reduced. Advantages of RTOS over other OS.
15. If a faulty thread is present which has infinite loop, explain how the scheduler handles it. How to fix this ?
16. How to determine merging in a linked list.
17. How to use two queue's to get the behavior of a stack.
18. What are the traversals available. Come out with a traversal technique which can print 1,2,3,4,5,6,7,8 for a tree shown below.
                   1
           2               3
     4         5      6     7
  8
19. How do you search for duplicate data in a linked list?
20. How to know if a data structure was modified when it is shared between different threads which can read, modify, delete data from it. What mechanism is followed in general.
21. How to debug a system hang.
22. How to debug a crash. Especially when the core file does not give proper information.
23. Priority inheritence explain.
24. What are the IPC mechanisms available.
25. How will the scheduler schedule the threads in a normal OS (i.e. Non premptive priority based). How will it handle when a thread malfunctions in the process.
26. Explain how security is achieved using SNMP V3.
27. How  do you determine Little endian or Big Endian. Write program.
28. Write prog for ntohs()
29. Explain STP, RSTP and MSTP. Which one is better top down or bottom top model for ST, w.r.t Root bridge position. Edge ports use.
30. How to detect a memory is corrupted? What are the mechanisms used?
31. What are the different signals you have used?
32. what are the different segments you know.
33. what is a heap data structure.
34. What happens if a ARP packet is L3 broadcast?
35. How do you implement a timer library.

Company Juniper: (interview : 5hrs)
1. Use of volatile keyword.
2. How to delete a data in a linked list using only single pointer.
3. Explain switching process.
4. What are the contents of table used for switching.
5.  Shared Vlans MAC Vlan table example.
6. Ingress filtering.
7. difference between L2 Broadcast and L3.
8. Compose a data structure for Semaphore.
9. Ntohl implementation.
10. given an array of 1's and 0's in random order, how will u arrange them in such a way that 1's are on one side and 0's on other.
11. How fragments are done? Where will they be joined ? Explain why?  Given 3 routers with different MSS.
12. Difference between binary and Mutex. Functions used .
13. ARP which layer protocol ? How is it useful.
14. 8 Queens problem
15. Basic switching explanation.
16. Size of structure without using arrays and sizeof.
17. What is hard time and soft time?
18. Use of Volatile?
19. Explain communication if a host is connected to a switch and then the gateway while doing a ping?

Company : Brocade ( interview : 1 .5 hrs telephonic)
1. Difference between trap and Inform.
2. Enhancements done in SNMP V2 over V1. V3 over V2 and V1.
3. How Security is achieved in SNMP V3.
4. Different types of error messages sent from agent.
5. Given three indices of string type, explain the order of Get-Next command output.
6. How are traps received by a manager.
7. What is the difference between counter and gauge.
8. What are the IPC mechanisms used by SNMP in a process based model
9. What are the ports used by SNMP.
10. Is it possible to do a SNMP V3 GET on  an agent that has been operating since 2 days even though no action was performed on the agent continuously.
11. Use of SNMP Engine ID.
12. few questions about MIB generation, Code generation to be used in the image.
13. What are the default traps available.
14. What are the contents of a trap.
15. What is a proxy agent.
16. Test tools used like Silver Creek, and questions relevant to them.
17. What are the initial messages exchanged between Manager and the Agent in a SNMP V3.
18. How are the counters populated and retrieved by the Agent.
19. Which is better, process based model or thread based model. Which is preferred when.
20. Why is it that only one port is used while tx and Rx in a LAG when the src mac address is the same. How do you address reordering problem in LAG. What if any specific frame is lost. Which layer handles loss of frames.
21. Difference between TCAM and normal CAM. What is advantageous. 
22. What are the contents of trap?

Company: Broadcom. (interview : 6 Hrs)
1. *p++ what does it do when assigned to any variable.
2. const char *p ,char *const p , const * char p differences.
3. inserting node in the middle of a linked list.
4. What is the difference between STP, RSTP, MSTP. Explain how the convergence is achieved in RSTP. What are the port states that are present in each of the versions.
5. Explain LAG. Why it is not supported on a half duplex port. What is a static LAG.
6. Given two images used intermittently in a single RAM, how do you ensure proper communication between the two images in case each image wants to share some information with other.
7. What is alignment for a structure node { char c1;int n1;char c2;int n2;}. How can you avoid alignment problems.
8. What is the difference in behavior between ingress filtering enabled and disabled. How will it behave for tagged and untagged frames received on a port.
9. What is an ACL, TCAM. How are the rules prioritized in ACL. What are the actions available. What will the TCAM do in case there are multiple similar rules. Will it check for all the protocols configured for denial or accept?
10. What are the IPC mechanisms in Linux.
11. Design process done in the company. Testing methodologies used.
12. What is the relation between STP and LACP. Any specific scenario?
13.What is QinQ? how is it used and where is it used
14. Explain all the process involved in retrieving the webpage yahoo.com
15. List all the protocols that are used in the above process.
16. what are SAP's in networking where are they?
17. What does a ping do? will it call the ICMP application ?

Company : Aricent (interview : 2hrs)
1. Frame format of Dot1Q. Use of TPID. What if the vlan id is 0? How does it classify.
2. How to see the contents of an archive file?
3. Explain STP, RSTP, MSTP differences.
4. Explain Link OAM and how it can be used to detect faults.
5. How is the Discovery process done in Link OAM. How are the errors notified to the customer? How can the loopback detect the problems. How the configuration is done. is there any default configuration that can be used?
6. const char *p and char *const p differences.
7. What is segmentation fault? which signal is used to indicate it.
8. What is volatile used for. What is the difference between volatile const char *p and const char *volatile p.
9. What is QinQ? how is it used and where is it used
10. Ingress filtering related questions.
11. A TCP socket is used in sendto(). Will the packet pass?
12. What happens when a fork is done. How will the scheduler adjust the time slice for it?
13. What are the different system calls that change the execution from user mode to kernel mode?
14. How is process different from a thread.
15. DIfference between Mutex and Binary semaphore?
16. Different IPC mechanisms used/available.
17. What is a zombie process?
18. What is padding problem? How can it be controlled? How is it handled using pragmas?
19. SNMP qns that are mentioned in Brocade were asked.
20. o/p of the program
 int main()
{
int *p;
p=value();
printf("%d",*p);
return 0;
}
int * value()
{
int p=100;
return &p;
}
21. What does a Malloc do. Return type of malloc.
22. Declare a function pointer.
23. Application of counting semaphore.
24. what are ACL's used for?
25. What is the ethertype for QinQ, VLAN.
26. What is the use of ioctl?
27. how are the sockets used for a communication link.
28. What is internal fragmentation and external fragmentation.
29. What is the difference between shared object and a library?
30. Use of Static key word. What are the different storage classifiers available.
31. Use of extern key word.
32. Difference between typedef and macro.

Company : HCL (interview time : 2hrs)
1. Write a macro to find maximum of two numbers. enhance it for 3 numbers.
2. Debugging command to add breakpoint.
3. How to debug a thread in gdb.
4. How to attach a core file in gdb.
5. What is priority inversion ? explain.
6. Tasks A,B,C are having priorities 100, 200, 255 respectively. Task C is holding a semaphore. Assuming priority inheritance is in place, if Task C wants a resource held by Task B, will it get the resource? if so what would be the priority of each task for that to be achieved. If not why?
7. How will free know how many bytes of memory to be freed? How is the sanity check implemented.
8. Write a program to delete a node in a Linked list.
9. Explain the timer library implementation, for a granularity of 1 sec given the efficiency should be only by time.
10. How will the interface number on which the response has to be sent is known to the SNMP Agent once it needs to send a reply?
11. Port numbers used for SNMP. What is inform?
12. Difference in SNMP v2 trap and v1 trap.
13. Questions related to VLAN, STP, RSTP, MSTP, LAG, ACL as discussed above in other companies.
14. How the Multicast Mac address is mapped from multicast IP address.
15. How are the control packets identified?
16. Ether type of VLAN, and QinQ. What is QinQ used for.
17. Use of Volatile keyword?
18. How a multicast communication happen. 
19. Declare a function pointer. What is the difference between (void *func)() and void (*func)().

Some Generic questions ( this keeps growing):
1. Use of register Keyword. Can it be declared globally.
2. Can a Macro be declared with variable arguments ? if so How?
3. Can a Nested function be declared? How?
4. Can a Macro with a goto statement and a label be defined? If so, what happens, if the same macro is called repeatedly thrice?

My Friends Interview Questions:

Brocade interview details for IP group
----------------------------------------
Round-1: Basically it's around L2 data path
------------------------------------------
1. What is the difference between switching and routing
2. What is the difference between switch and bridge
3. Explain VLAN classification
4. Explain about priority tagging
5. How VLAN is classified for priority tagged frames
6. An admin is observin that A MAC entry is getting toggled, what is    the problem and what is the solution(loop & STP)
7. How many STP PDUs are sent on a LAG?
8. Why LAG members are always of equal speed? [Other distribution will be
   unequal. And this is ASIC & usage problem. Nothing to do with LACP    protocol]
9. Why we need LAG hashing? What will happen if we don't have hashing?
   And why same session data is transferred always on same LAG member?
10. What is q-in-q. Why we need that?
11. What is VLAN translation and how it helps?
Then He came to "C" and "os" Qs
1. How you reverse a given statement?
2. How you can find duplicates in a given list?
3. How you trace stack fatals
That's all First round is done. :)
Round-2: It's more of design specific interview
------------------------------------------------
He asked only few questions, based on which arguments went in
1. What is q-in-q and why we need q-in-q
2. What all you consider while adding a port to a VLAN
3. What all you consider while adding an ACL to a port
4. What is 802.3ah and why we need that?
5. What is remote loop back, and how we achieve this and what for it is?
Then He came to "C" and "os" Qs
1. How you reverse a given statement? (Same old Q)
2. What is priority inversion?
That's all Second round is also done. :)
Round-3: It's more of protocol implementation
------------------------------------------------
1. What is STP and why we need that?
2. How we achive MSTP.
3. What is the impact of dynamic VLANs on MSTP?
3. HOW LAG and STP works?
4. Can a port be member of multiple LAGS?
 Third round is also done. :). Call is from USA. So he believed that
 I know thing well. ;)
Round-4: It's more of Managerial implementation (F2F in B'lore)
-------------------------------------------------------------
The call is with VP-1
1. What is conflict and how u resolve it? This point went for 30-min discussion.
2. How you can map your work to revenues? (How?)
He asked abt my pay at the end, and then started struggle. :(
Round-5: It's more of Managerial implementation (F2F in B'lore)
----------------------------------------------------------------
The call is with VP-2
1. How good u r at design?
2. Tell me about ur recenet work's design
3. Tell me the design part of malloc and free
4. Tell me why STP and why not STP?
5. Tell me about conflict? (Seems so much of conflicts are around ;))
6. Tell why you need that much salary? (I have many answers ;)
That's all then asked for a written test.
Round-6: Written test
-----------------------
It has 2 questions with it. It's 90-min span stuff.
1. Implemented a linked list with sorted insert
2. Write code for ls -t option.
And Then final Round: Round 7
---------------------------------
1. Explain packet flow path in the switch (All stages)
2. Explain packet flow path in the stack
3. Explain packet flow path in the chassis
That's all, done. Have fun!


Suggested Reading for Networking:
All New Switch Book.
For OS: Understanding Linux kernel 3rd Edition
Understanding Linux Network internals by OReilly Publishers.

The following link may be of help to you for some of the questions mentioned above.
http://profile.iiita.ac.in/pkmallick_03/adfaqpublish.html