582498 Internet Protocols, Fall 2015
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Exercise 6 (Week of October 12, 2015)


1. RIP, OSPF, and BGP protocols

   a) Assume a router has 30 routes to advertise using RIP.
      What happens if once an hour one of these datagrams is lost?
      How many routes will not arrive at the receiving neighbor?
      Is this a problem? Explain.

   b) The OSPF packet format has checksum field, but the RIP packet does
      not. Why?

   c) How do BGP routers detect routing information loops?

   d) Can the information provided by BGP in AS_PATH attributes be
      considered as a distance metric? Explain.

   e) Why does the BGP protocol need a KEEPALIVE message of its own? As
      BGP uses TCP protocol, why cannot it use the permanence of the TCP
      connection as the keepalive indication?


2.  A BGP router has collected the following path information to access
    the network 192.9.9.0. Show the network topology of Autonomous
    Systems that can be drawn from the collected information (i.e., How
    the different ASs are connected to each other).


   Network	Next Hop       	M/LP/Weight Path
 * 192.9.9.0  204.212.44.128 	0 	234 266 237 3561 701 90 i
 *           	205.238.48.3   	0 	2914 1 90 i
 *      	144.228.240.93 	0	1239 701 90 i
 *      	204.70.4.89    	0	3561 1 90 i
 *      	194.68.130.254 	0	5459 5413 1 90 i
 *      	202.232.1.8   	0	2497 701 90 i
 *      	158.43.133.48	0	1849 702 701 90 i
 *      	131.103.20.49 	0	1225 2548 1 90 i

  With the next hops being:

  blackrose.org (Ann Arbor) 204.212.44.128  through AS234
  Verio (MAE-WEST) 	205.238.48.3  	through AS2914
  Sprint (Stockton) 	144.228.240.93 	through AS1239
  MCI (San Francisco)	204.70.4.89   	through AS3561
  LINX   (London) 	194.68.130.254 	through AS5459
  IIJ   (Japan)  	202.232.1.8    	through AS2497
  PIPEX (London) 	158.43.133.48  	through AS1849
  IAGnet (Chicago) 	131.103.20.49  	through AS1225


3. Consider the network topology below consisting of multicast
   capable routers. 


             B --------------------------------------------- C
                                                             |
      E ---------------------------------- A                 |
      |                                    |                 |
      |                                    |                 |  
      H ------------------ I ------------- F --------------- D
      |                    | .                               |
      |                    |  .                              |
      |     L              |   .                             |
      |    .               |    .                            | 
      |   .                |     .                           |
      |  .                 |      .                          |
      | .                  |       .                         |
      |.                   |        .                        |
      K          M ------- N -- O    J --------------------- G



  Supposing that Reverse Path Multicasting (reverse path forwarding 
  with pruning) is in use and routers B, E, G, K, and J are attached to
  networks that have host(s) belonging to the multicast group in question.
  What kind of source-based multicast tree would be constructed for 
  the sender F? Explain how this tree is constructed.


4. a) What purpose is the IGMP protocol needed for?

   b) The lecture and lecture notes cover IGMPv2 in the first place.
      What differences can you find in IGMPv3 compared to IGMPv2? Not
      small detailed differences are seeked for, but higher level
      differences that are also visible in the packet format.


IPv6 muticast addressing ....

5. What problems occur, when a mobile node moves to another subnet 
   (an IP network with a different network prefix)? How Mobile IP
   solves the problem. What protocol actions are needed? Why the
   Mobile IP based solution may be inefficient?


6. What challenges sending multimedia (e.g., audio, video) over the
   Internet encounters? What requirements multimedia typically presents
   to the packet delivery? What is the main problem and why/how does it
   arise? What measures applications can take to mitigate the problems?


7. Your opinions on this course.

   a) What topics were, in your opinion, the most interesting and
      important ones? What topics were dull or unnecessary?

   b) How should the course be changed in the future? What should be
      more and what less? What missing topics should be included? Which
      topics deserve more attention in the lectures and practise
      sessions. Which topics deserve less attention?


   c) Fill in the teaching evalution form for this course available at
  
        http://ilmo.cs.helsinki.fi/kurssit/servlet/Valinta?kieli=en 

      Thank you!