Computer Science 881
                            Quiz 3             Name_______________________

1. For each of the following actions indicates whether it occurs
   in the context of an application process (A), context of a
   hardware IRQ (H) or the context of a software IRQ (S). (If
   multiple answers can apply, supply them all).


   _____ a. Extracting the network layer protocol ID (IP, ARP, etc) from
            the MAC header

   _____ b. Enqueuing a received sk_buff on the receive queue of a struct sock


   _____ c. Reassembly of a fragmented IP packet


   _____ d. Dequeuing a received sk_buff from the receive queue of a struct sock


   _____ e. Enqueuing a received sk_buff on the softnet data structure


   _____ f. Copying received data from the kernel buffer back to user space


2. Describe two conditions under which an unfragmented UDP packet that has been
   correctly received by the device driver and IS deliverable to an open socket
   might be discarded instead of being delivered.


   a -



   b -



3. Suppose a unicast UDP packet receives a maximum "score" of 2 in the
   socket matching algorithm but it receives a two on multiple sockets.
   To which socket(s) is the packet delivered.






4. In  IP reassembly a single instance of a struct ipq represents

   a. a single fragment              b. a single packet being
                                        reassembled
   c. all packets presently
      being resassembled.

5. When a fragement is received and its head-end overlaps the tail-end
   of a single fragment that has already been received

   a. the overlapped tail of the      b. the overlapping head of the
      existing fragment is               new fragment is discarded
      discarded

   c. the ENTIRE existing overlapped  d. the entire new fragment is
      fragment is discarded.             discarded

6. Answer the following T or F


   ____ a. In reassembly the value of "meat" in a struct ipq can never exceed
           the value of "len"

   ____ b. A fragment with MF=0 must have an "end" value < qp->len to be
           acceptable.

   ____ c. It is never possible for "meat" to equal "len" until reassembly
           completes

7. How can the IP Fragmentation mechanism be used to generate a DoS attack
   and how does Linux defend against it?









 8.  Under what conditions does net_rx_action() return to do_softirq()

     a.


     b.


     c.


9. In the final stage of reassembly

   a. under what condition is it necessary to dynamically create a new sk_buff and
      insert it into the fragment chain.





   b. At what location in the fragment chain will the newly created sk_buff
      reside?





   c. what data does that buffer own





10. What does UDP do with a packet that exceeeds the length of the buffer
    provided by the application