Homework #4 Grade Distribution:
| Points | Frequency |
|---|---|
| 35 | 4 |
| 36 | 0 |
| 37 | 2 |
| 38 | 0 |
| 39 | 10 |
| 40 | 0 |
| 41 | 9 |
| 42 | 0 |
| 43 | 7 |
1. 5.2 (max 14 points)
2 points each for correctly identifying each class
2 points extra for explaining why
Class A,B, and C addresses have 1,10, and 110 prefixes respectively.
Hence, addresses with the value of the first 8 bits
in the range of 0-127 are Class A, 128-191 Class B, and 192-223 Class C.
a) Class B
b) Class A
c) Class B
d) Class C
e) Class A
f) Class C
3. 5.12 (max 12 points)
2 points for hops from your host to other host(s)
2 points for how many hops to leave your local site
8 points for explaining how traceroute works
Traceroute sends UDP probe packets with the time to live (TTL) field set initially to one. Successive probe packets are sent with the TTL field incremented by one each time. A gateway that decrements a packet's TTL value to zero, drops the packet and sends to the source of the packet a TIME_EXCEEDED message using the Internet Control Message Protocol (ICMP). Probe messages are sent to unlikely destination ports, so that when a probe packet finally reaches its destination, ICMP will generate a port unreachable message and send it back to the source of the packet. Traceroute proceeds until a probe packet reaches its destination or the max TTL value is exceeded (the default is 30 hops). From this information traceroute can reconstruct a forward path to a destination host (if one was found).
3. 5.13 (max 17 points)
3 points for each packet's next hop
2 points extra for explaining why
Apply each subnet mask and if the corresponding subnet number matches the SubnetNumber column, then use the entry in NextHop.
a) Applying the subnet mask 255.255.255.128, we get 128.96.39.0. Use interface0 as the next hop.
b) Applying subnet mask 255.255.255.128, we get 128.96.40.0. Use R2 as the next hop.
c) All subnet masks give 128.96.40.128 as the subnet number. Since there is no match use the default entry. Next hop is R4.
d) Next hop is R3.
e) None of the subnet number entries match, hence use default router R4.