Computer Science 881
                            Quiz 3             Name_______________________


1. Under precisely what condition(s) under might a call to sys_sendto()
   result in the calling process being forced to sleep without
   passing the packet on to the physical device driver?








2. Under precisely what conditions(s) might a correct and routeable
   UDP packet be dropped for congestion by the protocol stack
   before being conveyed to the device driver?









3. Under what condition(s) might a packet that is dequeued by
   pfifo_fast_dequeue() NOT be the last packet that was enqueued by
   pfifo_fast_enqueue() (Assume a UNI processor system here.. but
   also assume the CORRECT no-preemption in kernel mode model used
   in Linux)










4. For a non-connected UDP socket which of the following must be non-zero
   in the struct sockaddr_in or the transmission attempt will be
   rejected.

   a. dest port                    b. dest IP address

   c. source port                  d. both a. and b.


5. For disconnected sockets it is necessary to:

   a. call ip_route_output for every packet sent

   b. call ip_route_output only when the route associated
      with the struct sock has become stale or for the first packet
      sent on the socket


6. In the UDP path we have studied so far, indicate whether each of the
   following actions occurs in (U) user process context,  (S) soft irq
   context or (B) both soft irq and user context, or (H) hardware IRQ.

   ___ a. dequeuing an sk_buff with pfifo_fast_dequeue


   ___ b. enqueing an sk_buff with pfifo_fast_enqueue


   ___ c. enqueuing an sk_buff on the completion_queue of the CPU's
          softnet_data structure.


   ___ d. invoking the device drivers hard_start_xmit function


7. What is the main disadvantage of having the device drivers Tx ring
   configured with

   a. too many slots




   b. too few slots




8. The netfilter facility allows firewalls to install hooks that
   inspect packets.  Which best characterizes the normal operation
   of such hooks

    a. the packet is allowed to pass if ANY hook accepts it

    b. the packet is dropped if ANY hook says to drop it

    c. both a. and b. are true


9. Suppose the R and C bits of the IP TOS are 1 and the D and T are 0.

   a. What numeric "priority" does this setting correspond to??





   b. Which of the three standard priority queues does this setting
      map to?







10. Identify two conditions that will force the "slow path" to be taken
    in ip_build_xmit