Juniper networks phone interview

Just had a phone interview from Juniper networks. Don't think I'll get it since a lot of things I either don't know or messed up. Either way this is probably the toughest phone interview I had so far, and the kind of questions I actually expect from other companies. The interviewer first asked me if I had any other job offers, and if I need visa sponsorship, then he went right to the questions. Below are the questions I can remember, I'll try to prove the answers that I know (might not be correct!)

1. Count the number of 1s in an integer

2. Difference between little-endian and big-endian

Q1 and Q2 are in Programming Interviews Exposed


3. If uint32 *p = 100, what's the value of p after ++p
should increment by the size of the uint32 (I think)

4. What is a system call
from wikipedia, a system call is a mechanism for an application to request service from the OS.

5. Follow 4. Something about write() and strcpy()
write() is a system call

6. what does keyword volatile in C do
it tells the implementation to suppress optimization

7. Something about spinlock

8. Difference between semaphore and mutex
Since I never did any thread programming, I can't answer these two at all :-( But here are some answers.

9. difference between TCP and UDP
TCP is connection-oriented, reliable, in order delivery, and has congestion control

10. When to use TCP and UDP
TCP, when we cannot afford packet loss. UDP, time sensitive applications, voice, video etc

11. System function calls for a simple server
socket()->bind()->listen()->accept()

12. is listen() blocking?
listen() is nonblock and accept() after listen is default blocking. Note: recv() also blocks <- failed at this one

13. difference between SOCK_STREAM and SOCK_DGRAM SOCK_STREAM-> TCP, SOCK_DGRAM->UDP

14. What does the keepalive option in socket() do?
it's a heartbeat that periodically (usually 2 hrs) checks if the TCP connection is still valid.

15. can udp use connect()? what does it do?
Yes, udp can use connect(), it filters the incoming packets to certain hosts or certain port. <- not very sure A better explanation. It simply tells the OS the address of the peer. No handshake and no data is sent. Once is connected, client can use sendto() with null address, and can use send(), recv(), read(), write().

16. describe select(), what is the disadvantage of select() select monitors several sockets (file descriptors) at the same time, and let you know which one is ready so you can do further processing. disadvantage? No idea, but here are some answers

17. What is MTU/Path MTU
MTU = maximum transmission unit. The max size of a packet that the layer can handle. Path MTU, the max size of packets between a path (2 end points) can have without fragmentation. Wiki

18. describe how traceroute works
basically we sent out a series of ordinary IP packets (UDP datagram), each with increasing TTL value (1, 2, etc) and a random port. When TTL expires, the router returns a TTL expired ICMP message. When it reaches the destination, the destination returns a port unreachable ICMP message.

19. what does SOCK_SEQPACKET do?
Never seen this before, but I think I actually gave out the right answer. Here is a better explaination. Basically, it's either a sequence of packets which are delivered reliably and in order, or a reliable, ordered stream with record boundaries in it.

And there's also a question ask me to explain one of my project (id-based routing protocol). Overall I think I am ok with networking concepts, but I really need to do more study on the basic C/thread programming/socket programming stuff.