HW 3

Read chapters 9 through 12 of your text and the reading assignment on DWDM.

Not all problems below are assigned. Visit the course management website to check on the assigned problems (which vary each semester). Add your answers following the assigned problems.

CH 9 ***

1. Under what circumstances might IP fail to deliver a datagram?

2. To allow _______________ in an internet to report errors or provide information about unexpected circumstances, the designers added a special purpose mechanism known as _____________________________.  This mechanism is a _______________________ part of IP.  The _________________________________ provides communication between the ____________________________ software on one machine and the _________________________ on another machine.
3. Where are ICMP error messages reported to?
4. How many levels of encapsulation are used to send an ICMP message across a network?
5. The first three fields of an ICMP message are identical for all ICMP messages.  What are those fields and how are they used?
6. Sketch an ICMP Echo Request header, label the fields and indicate their size.
7. What should the receiver of an echo request do with the data in the data field of the echo request?
8. What would be indicated by an ICMP reply regarding an IPv4 packet that failed to reach its destination if the ICMP message had TYPE 3 and CODE 4 in the header?
9. Why would an ICMP redirect message be sent from a router to a host?
10. What ICMP message is sent back to the original sender of a datagram to indicate that the datagram’s TTL field had been decremented to zero before the datagram could be delivered?

CH 10 ***

11. Sketch a UDP header and label the fields.  Below this, indicate the purpose and use of each field.
12. What is a UDP pseudo-header for IPv4 and how is it used?
13. What are some “well-known port numbers” for UDP?
14. Why is UDP considered a “thin protocol”?

CH 11 ***

15. Why does a sliding window protocol provide better throughput than a simple positive acknowledgment protocol?
16. Sketch a TCP header, label the fields and indicate the number of bits for the various fields.
17. What purpose does the SEQUENCE NUMBER field serve?
18. Explain the purpose of the FIN and RST bits when they are set to 1.
19. What purpose does the URG bit and the URGENT POINTER field serve and how do these work together?
20. Sketch a TCP pseudo header and explain how this header is used.
21. What TCP technique is used to recover once congestion ends?
22. How would tail-drop be carried out as a method of flow control?
23. How is a TCP connection closed?
24. What is a finite state machine and what is the difference between a Passive Open and an Active Open?
25. What are some examples of TCP’s “well-known port numbers”?
26. What is silly window syndrome and how is it avoided (in general)?

CH12 ***

27. Except for destinations on directly attached ______________, hosts pass all IP traffic to ___________ which forward ____________ on toward their final destinations.  A __________ travels from router to router until it reaches a ____________ that attaches directly to the same __________ as the final destination.
28. Consider figure 12.2 in your text.  A ring based backbone connects to the routers of three customers (R1, R2 and R3). Routing in this circumstance is described as consistent but inefficient.  Why is it consistent? Why is it inefficient?
29. An incoming routing update, shown fig. 12.5 (b), will cause changes to some entries in the initial routing table shown in fig. 12.5 (a).  Write out the routing table after the updates are completed.
30. List some disadvantages of distance-vector routing algorithms.
31. What concerns arise for routers that use UDP segments in IP datagrams to exchange routing updates?
32. What are the advantages of using a link-state routing protocol when compared to a distance-vector protocol?
33. Why don’t distance-vector routing protocols scale well?

DWDM ***

34. Why was DWDM developed?
35. What economic advantages does DWDM service provide?
36. What equipment must change to make use of DWDM?
37. Briefly, how does DWDM solve the capacity crisis encountered in service provider backbones?
38. What is meant by “incremental growth” and why is that important?
39. Why does DWDM improve the “distance” between repeaters in the optical network?

Advanced Subnetting ***
The Subnetting DVD will help with the easier problems; thought will help with the theoretical problems.

40. Determine the first useable address, the last useable address, the network address, the subnet mask and the subnet broadcast address for the 125th useable subnet when subnetting the following:
41. 10.0.0.0 when borrowing 14 bits
42. 172.20.0.0 when borrowing 7 bits
43. Determine the first useable host address, the subnet mask and the subnet broadcast address for the 3,278th useable subnet on network 10.0.0.0 when 13 bits are borrowed for subnetting.
44. Though there are practical reasons why we don’t complicate our lives this way in the real world, from a theoretical perspective we could borrow non-consecutive bits for subnetting. So, when borrowing the first host bit, the second host bit and the last two host bits (counting from the left of the host bit field) from 172.1.0.0 can you determine the following:
45. subnet mask
    b. network address for 0th subnet, 1st subnet and 2nd subnet?
    c. total number of subnets and number of useable subnets?
    d. number of remaining host bits and then the number of useable hosts on a subnet?
    e. First useable host on the 2nd useable subnet?
    f. broadcast address for 2nd useable subnet?
    g  1,203rd useable host address?
46. Another theoretical problem. Counting from the left, borrow bits 9, 11, 13, 17, 18, 22, 28, 29 and 31 for subnetting from 10.0.0.0 and determine the following:
47. subnet mask
    b. network address for 55^th usable subnet, 171^st usable subnet and 317^th usable subnet?
    c. total number of subnets and number of useable subnets?
    d. number of remaining host bits and then the number of useable hosts on a subnet?
    e. First useable host on the 55^th useable subnet?
    f. broadcast address for 171^st useable subnet?
    g  803rd useable host address on 317^th usable subnet?
48. [Theoretical] A student has configured a software router and a workstation on a private LAN. He has set up the network with IP address 10.0.0.0 with subnetting that borrows bits 15, 16 and 17 (ONLY bits 15, 16 and 17, counting from the left) to create eight subnets (six useable).  The student has configured a workstation on the second useable subnet as the lowest available host IP address. The router has the highest usable address on this subnet for its interface connection to this network. The student has set up the workstation using the 138^th useable IP address on this subnet. What are these three IP addresses in binary? What are these addresses in dotted decimal?
49. You are reviewing a conceptual binary addressing scheme that uses 35 bits for network layer addressing (divided into seven 5-bit blocks that are written in dotted decimal format). The first and second subnetworks are reserved for the wire address and to support the broadcast address. The first and second host addresses on each subnet are also reserved to support the subnetwork wire address and subnet broadcast address. Network (N), subnet (s) and host (h) bits are arranged in the following manner with the left most bits of each type being the high order bits:

h h h s s . h h s s s . N N N N N . N N N N N . N N N N N . s s s h h . s s h h h

Determine the following for this theoretical network address space:

1. How many major networks are supported?
2. How many useable subnets are available on each network?
3. How many addresses are available for assignment to hosts on each subnet?
4. For the entire address space, how many useable host addresses are available?
5. Given the following address:

   11.30.8.0.17.4

   What Major network address does this host belong to?
   What subnet address does this host belong to?
   What would be the broadcast address on this subnet?

6. Determine the dotted decimal address for the 834^th useable host on the 1000^th useable subnet of the 7,351^st major network.