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Midterm Test #2 Answers
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- Ian! D. Allen - idallen@idallen.ca - www.idallen.com

Test #2 Written Answer Section - Points: 68  (20 of 20%)

Read both sides!  Closed book.  No aids.  No electronic devices.

  1.   [Points: 1] The single 32-bit TCP header Acknowledgement number
       permits selective acknowledgement of packets, e.g. I got packets 1,
       2, and 4 (but not 3): FALSE

  2.   [Points: 1] The IP packet header contains IP addresses and port
       numbers: FALSE

  3.   [Points: 1] When reading the ABNF rules given in RFC documents,
       quoted strings (e.g. "HELO") are not case-sensitive: TRUE

  4.   [Points: 1] When two systems attempt simultaneous TCP connections
       with each other, the protocol ensures that they end up with one
       single bidirectional TCP stream, not two streams: TRUE

  5.   [Points: 2] Describe briefly two functions of ICMP on the Internet.
       [Announce network errors, Announce network congestion, Assist
       Troubleshooting, Announce Timeouts, etc.]

  6.   [Points: 1] What interior/internal routing protocol
       is replacing the old RIP protocol? [OSPF]

  7.   [Points: 1] What Unix/Linux system call allows you to
       manipulate TCP/IP options such as SO_REUSEADDR? [setsockopt()]

  8.   [Points: 1] Why aren't the source and destination IP addresses
       given in the TCP/UDP header? [they are in the IP header]

  9.   [Points: 2] Describe two ways your program can know
       it has read all bytes sent from a remote client: [send the number
       of bytes at the start or use a record-termination sequence (e.g
       NL) to signal end of data segment]

  10.  [Points: 4] The TCP sliding window feature classes bytes into four
       categories.  Describe each.
       http://www.tcpipguide.com/free/t_TCPSlidingWindowDataTransferandAcknowledgementMech.htm
       #1: Bytes Sent And Acknowledged
       #2: Bytes Sent But Not Yet Acknowledged
       #3: Bytes Not Yet Sent For Which Recipient Is Ready
       #4: Bytes Not Yet Sent For Which Recipient Is Not Ready 

  11.  [Points: 2] What does TCP "slow start" mean?  How does it work? 
       Why is it needed?
       http://www.tcpipguide.com/free/t_TCPCongestionHandlingandCongestionAvoidanceAlgorit-2.htm
       ["Each sender is at first restricted to sending only an amount
       of data equal to one "full-sized" segment-that is, equal
       to the MSS value for the connection. Each time an acknowledgment
       is received, the amount of data the device can send is increased
       by the size of another full-sized segment." [...] "In a busy
       internetwork the sudden appearance of a large amount of new
       traffic could exacerbate any existing congestion."]

  12.  [Points: 3] Show, in order, the TCP flags used in the basic TCP
       three-way handshake.  Clearly indicate which flags are sent by
       server and which by client. [C=SYN; S=SYN,ACK; C=ACK]

  13.  [Points: 2] Describe briefly two reasons why IP packet
       fragmentation should be avoided. [inefficient use of resources,
       degraded performance (in reassembly, fragment loss), lack of
       efficient reassembly]

  14.  [Points: 2] What is the content and purpose of the
       TCP and UDP "pseudo-header"?  (Why is it necessary?)
       ["contains the source address, the destination address, the
       protocol, and the UDP length. This information gives protection
       against misrouted datagrams."]

  15.  [Points: 2] What happens when a Unix/Linux process
       writes data onto a closed socket, e.g. using write() or send()?
       [SIGPIPE is sent to the process]

  16.  [Points: 2] Why does client.c (Lab 4) need to use a shutdown()
       system call?  What is being shut down and why?  [shut down writing
       half of server socket to create EOF at server - because socket is
       open in two processes and therefore close() will not generate EOF]

  17.  [Points: 10] In your exam booklet, write detailed PDL
       for a TCP port scanner.  (This detailed PDL represents all the
       code you wrote for Lab 3.)  [see your class notes]

  18.  [Points: 20] In your exam booklet, write detailed PDL
       for the forking multi-process "echo"-style server that accepts
       multiple client connections and loops the client data received
       back to the client.  (This detailed PDL represents all the code
       you wrote for server2.c in Lab 4.)  Do not include the PDL for
       the sendall() function.  Pay close attention to the handling of
       all socket descriptors.  [see your class notes]

  19.  [Points: 10] In your exam booklet, write PDL for the
       forking multi-process echo client that connects to the above
       echo server.  (This detailed PDL represents all the code you wrote
       for client.c in Lab 4.)  Give the detailed PDL for the creation
       and management of the parent/child processes and sockets.  Do not
       code any PDL for the two read/write loops in the client.  Do not
       code any PDL for the sendall() function.  Pay close attention to
       process management and the handling of all socket descriptors.
       [see your class notes]