## COSC 4377 - Introduction to Computer Networks Section 07662 Spring 2001

### Due in the class, on Monday, April 9, 2001

There are 5 questions, 4 written ones and one expirement. Each question weights 20 points.

1. From Kurose & Ross, Chapter 4, Problem 3:
2. From Kurose & Ross, Chapter 4, Problem 6:
3. Just for reference: You might want to practice Kurose & Ross, Chapter 4, Problem 4 for the exam also. You don't have to turn in this question.
4. From Peterson & Davie, Chapter 4, Exercise 38:

Table 4.14 (below) is a routing table using CIDR. Address bytes are in hexadecimal. The notation "/12" in C4.50.0.0/12 denotes a netmask with 12 leading 1 bits, that is, FF.F0.0.0. Note that the last three entries cover every address and thus serve in lieu of a default route. State to what next hop of the following will be delivered.

```		-----------------+----------
-----------------+----------
C4.50.0.0/12     |     A
C4.5E.10.0/20    |     B
C4.60.0.0/12     |     C
C4.68.0.0/14     |     D
80.0.0.0/1       |     E
40.0.0.0/2       |     F
00.0.0.0/2       |     G
-----------------+----------
Table 4.14
```
1. C4.5E.13.87
2. C4.5E.22.09
3. C3.41.80.02
4. 5E.43.91.12
5. C4.6D.31.2E
6. C4.6B.31.2E
5. From Peterson & Davie, Chapter 4, Exercise 39:
6. Suppose P, Q, and R are network service providers, with respective CIDR address allocations (using the notation of Exercise 38) C1.0.0.0/8, C2.0.0.0/8, and C3.0.0.0/8. Each provider's customers initially receive address allocations that are a subset of the provider's. P has the following customers:

PA, with allocation C1.A3.0.0/16 and
PB, with allocation C1.B0.0.0/12.

Q has the following customers:

QA, with allocation C2.0A.10.0/20, and
QB, with allocation C2.0B.0.0/16.

Assume there are no other providers or customers.

1. Giving routing tables for P, Q, and R assuming each provider connects to both of the others.
2. Now assume P is connected to Q and Q is connected to R, but P and R are not directly connected. Give tables for P and R.
3. Suppose customer PA acquires a direct link to Q, and QA acquires a direct link to P, in addition to existing links. Give tables for P and Q, ignoring R.

### 5. Traceroute:

This problem requires you to run a traceroute from your computer to some hosts and count number of hops required to reach the destination and also record the latency to reach the destination. You can run "traceroute using any of the following ways.

• from textbook companion website,
• run "tracert" on your Windows 95/98/NT/2000 machines, or
• if you have an account on bayou, you can run "traceroute" at prompt or /usr/sbin/traceroute if it can't be found. Here is the man page of traceroute. It contains detail info about the command line parameters and the format of output.
• There is a web site called www.traceroute.org. This site provides links to hosts all over the world which provide interfaces to run traceroute from their local machines or routers. So you can run traceroute from Finland (EUNet) or Italy (IHnet).
• There is an interesting shareware called VisualRoute which shows the traceroute path on a world map. It's very cool. And you can also try their live demo on 7 VisualRoute servers around the world (using JAVA as interface).

Here is what you need to do. First of all, pick three (3) of the following hosts and label them as H1, H2, and H3.

Secondly, pick two hosts as routers from www.traceroute.org and label them as R1 and R2. Also, record their host names.

Thirdly, run traceroute from source (R1 and R2) to destination (H1, H2, and H3). Record number of hops and latency between source and destination. You should have 6 values for number of hops and 6 values for latency.

Fourthly, pick a home site. You can use your own PC (running Linux/BSD/Windows 95/98/NT/2000), bayou, or any host from www.traceroute.org (other than R1 and R2). We will label it as HS. Record host name or IP address of HS.

Fifthly, run traceroute from source (HS) to destination (R1, R2, H1, H2, and H3). Record number of hops and smallest latency between source and destination. You should have 5 values for number of hops and 5 values for latency.

Now draw a graph similar to this one. Replace H1, H2, H3, R1, R2, and HS with their host names or IP addresses. Label each link with number of hops and latency.

Finally, calculate the total number of hops and latency between home site (HS) and hosts (H1, H2, and H3). Also, calculate the total number of hops and latency from home site (HS) via routers (R1 or R2) to hosts (H1, H2, and H3). You will have a table like this.

 Paths # of hops Latency (msec) HS-H1   +   HS-H2   +   HS-H3 HS-R1-H1   +   HS-R1-H2   +   HS-R1-H3 HS-R2-H1   +   HS-R2-H2   +   HS-R2-H3

#### Questions you might have:

• Question: When calculating latency time from host to destination, which values do we use in the traceroute result? Each hop has 3 time fields listed after it. I'm not sure which to use.
Answer: Traceroute lunches 3 probes (by default). Just pick the smallest one.
• Question: What number in the output of traceroute should we use as the latency?
Answer: Here is an example (traceroute to HBU - Houston Baptist University).
```Bayou.UH.EDU> traceroute www.hbu.edu
traceroute to www.hbu.edu (206.97.180.13), 30 hops max, 40 byte packets
1  caesar-atm12-00-1.gw.uh.edu (129.7.1.251)  1 ms  2 ms  0 ms
2  a1-3-1-0-3.a01.hstntx01.us.ra.verio.net (128.241.2.33)  2 ms  2 ms  2 ms
3  ge-0-1-0.r00.hstntx01.us.bb.verio.net (129.250.30.209)  2 ms  2 ms  2 ms
4  p4-4-0-0.r01.dllstx01.us.bb.verio.net (129.250.3.193)  7 ms  7 ms  7 ms
5  p4-2-0.r00.dllstx01.us.bb.verio.net (129.250.3.73)  7 ms  7 ms  8 ms
6  core4-serial0-0-0-0.Dallas.cw.net (204.70.10.77)  8 ms  9 ms  8 ms
7  corerouter2.Dallas.cw.net (204.70.9.150)  20 ms  10 ms  12 ms
8  acr2-loopback.Dallasdan.cw.net (208.172.130.62)  9 ms  10 ms  9 ms
9  aar1-loopback.Dallasdan.cw.net (208.172.130.2)  10 ms  10 ms  9 ms
10  internet-access-point-corp.Dallasdan.cw.net (208.172.135.18)  15 ms  16 ms  15 ms
11  gateway-005.Houston.iapc.net (204.71.92.23)  17 ms  22 ms  18 ms
12  206.97.180.1 (206.97.180.1)  22 ms  21 ms  20 ms
13  206.97.180.13 (206.97.180.13)  23 ms  22 ms  22 ms
```
There are 3 numbers (23ms, 22ms, 22ms) in very last line (No. 13). They are round-trip time to the destination. So you should pick the shortest time and divide it by 2. In this case, the latency between bayou.uh.edu to www.hbu.edu is 11ms.
One interesting observation is that the route from UH to HBU actually goes through Dallas and come back to Houston, although HBU is located in the southwestern side of Houston.