Review Questions:
Brett Lee
==============================================================================


1.  In establishing a TCP connection, what three packets are exchanged and in
    what order?

2.  In a /17 subnet, how many usable IP's are there?

3.  In a unix filesystem, "files" have three properties associated with them.
    What are the names of these properties ?

    part 2: what does "ctime" reflect?

4.  Rank these actions from fastest to slowest:
     - reading from cache
     - context switch 
     - reading from RAM
     - reading from a register

5.  How many bytes are in a MAC address?

6.  What does setting the sticky bit on a directory do?

7.  What transport layer protocol does DNS use?

8.  Explain the difference between a hard link and a symbolic link?

9.  Using your favorite language, how would you print out the lines of a file
    in reverse order?

10. Explain the entire process that occurs after typing in 'telnet foo.com'?

11. What is a context switch?

12. What is the valid range of exit codes from an 8-bit program?

13. What do you get when you bitwise AND the IP address && subnet mask?

14. How would the OS determine the broadcast address for an IP subnet?

15. How does the OS determine where to route the packet?








Answers:
----------------

1.  SYN, SYN-ACK, ACK

2.  32766
 
    /17 = 255.255.128.0 = 11111111.11111111.10000000.00000000
    count the 0's - you get 15, so: (( 2^15 ) - 2) = 32766

    or, remember that:
      /24 = 11111111.11111111.11111111.00000000 = 256 
      /16 = 11111111.11111111.00000000.00000000 = 65536
    then you can just double (or half) your way between /16 and /24.

      i.e.  /17 = (( 65536 / 2 ) - 2 ) = 32766

3.  mtime, atime, ctime
    part 2:  the last time the inode (not the file) was changed

4.  I don't know for sure.  :)  Here's what I think.

    If both contexts are in the CPU cache:
      Reading from a register
      Reading from cache
      Context switch
      Reading from RAM
    If one context is (even partially) in RAM:
      Reading from a register
      Reading from cache
      Reading from RAM
      Context switch

5.  How many bytes are in a MAC address?
    Six:  01:02:03:04:05:06
    A MAC address is 48 bits long.
    This means that there are 281,474,976,710,656 (2^48) possible MAC addresses.
    A byte is 8 bits, and the range of decimal values for 8 bits is 256 (0-255).
    In Hex format, this range is represented by two characters (00-FF).
    Remember your bits:   0000 = 0
                          0001 = 1
                          0010 = 2
                          ...
                          1111 = F 
        So 4 bits makes up half a byte (a nibble), and 8 bits make a byte (FF).
        A MAC is 6 bytes, and six bytes times 8 bits per byte is 48 bytes.

6.  What does setting the sticky bit on a directory do?
    see:  http://www.etpenguin.com/docs/pub/Reference/DOC_permissions.txt

7.  What transport layer protocol does DNS use?
    It can use either UDP or TCP.  UDP is typically used for requests, but
    TCP must be used for zone transfers.

8.  Explain the difference between a hard link and a symbolic link?
    see: http://www.etpenguin.com/docs/pub/Reference/DOC_inodes.txt

9.  Using your favorite language, how would you print out a file in reverse?
    see:
      http://www.etpenguin.com/docs/pub/Language/_C-C++/C/file/reverseAfile.c
    or, from Perl:
      perl -0777e 'print scalar reverse <>' f1 f2 f3 ...
        courtesy of http://www.ibm.com/developerworks/linux/library/l-p102.html

10. Explain the entire process that occurs after typing in 'telnet foo.com'?
    see: http://www.etpenguin.com/docs/pub/Reference/DOC_TCPconnect.txt"

11. What is a context switch?
    see: http://www.etpenguin.com/docs/pub/Reference/DOC_operation.txt

12. What is the valid range of exit codes from an 8-bit program?
    see: http://www.etpenguin.com/docs/pub/Reference/DOC_exit-codes.txt

13. What do you get when you bitwise AND the IP address && subnet mask?
    Answer:  The network ID.  
    example:
    192.168.0.2/24 = 
    192.168.0.2 && 192.168.0.0 =
    11000000.10101000.00000000.00000010 && 11111111.11111111.00000000.00000000 =
    11000000.10101000.00000000.00000000/24 =
    192.168.0.0/24 ( 11000000.10101000.00000000 )

14. How would the OS determine the broadcast address for an IP subnet?
    Find the network ID (Q.13) and fill the remaining bits with "ones."

15. How does the OS determine where to route the packet?
    see: http://www.etpenguin.com/docs/pub/Reference/DOC_packetrouting.txt