Internet Protocol

Overview

Fundamental to any large network is the protocol that provides switching services to the upper layers. This is the service that will move data from one place in the network to the other through a system of switching devices, and it may provide other services as well. We are going to look at the Internet Protocol or IP as an example of that service. There are others, but certainly none as ubiquitous as IP, which is part of the ARPA protocol stack and provides the basic packet switching services on the Internet.

Preparation

Read section 4.1 in the text and the notes.

Things to Think About

• If you had a collection of switches and/or routers, what type of protocol would you use to provide packet switching across the network - simplex unreliable, sliding window, ...?
• Would you choose packet switching or virtual circuit switching? Why?
• A major issue is addressing across a heterogeneous network (lots of different types of devices, physical layers, etc.). What kind of an address would you choose and why?
• What type of routing method would you choose? Why? Would you have only one or would there be different methods for different situations?
• What would you do if you had to consider physical layer networks with different maximum frame sizes?

Knowledge, Comprehension and Problem Solving

Terms

• Class [A,B,C] IP address
• Fragmentation
• ICMP
• IP Checksum
• Fragment offset
• Quality of service (precedence, throughput, delay, reliability)
• Address redirect
• Source quench
• Store-and-forward
• Subnetting

Questions

1. What are the classes of the following IP addresses?
   1. 128.36.199.2
   2. 21.12.240.17
   3. 183.194.76.253
   4. 192.12.69.248
   5. 89.3.0.1
   6. 200.3.6.2
   7. 153.90.192.1
2. What is the range of addresses for class B addresses?
3. A TCP message contains 2048 bytes of data and 20 bytes of TCP header. It is passed to IP for delivery across 2 networks. The first uses 14 bytes of header and has an MTU of 1024 bytes; the second uses 8-byte headers with an MTU of 512 bytes. Each networks' MTU gives the maximum packet size that may be sent, including the network header. Give the size and offsets of the sequence of fragments delivered to the network layer at the destination host. Assume all IP headers are 20 bytes.
4. A subnet has a host on it with the IP address 153.90.199.47 and an address mask of 255.255.248.0. What is the range of addresses contained in this subdomain?
5. Given the following routing table, show what the router would do with each of the packets:

Address	Mask	Send To
136.12.0.0	255.255.0.0	Interface 0
136.12.5.0	255.255.252.0	Interface 1
136.12.1.0	255.255.252.0	Interface 2
default		Interface 3

1. 136.12.135.145
2. 136.12.249.202
3. 136.12.29.1
4. 136.12.192.45

Analysis, Synthesis and Evaluation

1. What could be done to the IP address scheme make it easier on routers?
2. Under what conditions should an IP packet be discarded?
3. Why is it impossible for an IP network to control congestion problems caused by poor routing? What is the solution? Explain why the Source Quench option is a poor solution.
4. Using pseudocode, write the switching algorithm for IP.
5. Why do you suppose they didn't make the routing algorithm a part of the definition of IP since it obviously has to do routing?
6. Justify the existence of the TTL, Protocol and TOS fields in the IP format.
7. Discuss the advantages and disadvantages of reassembling packets at the receiver versus reassembling at the next router.
8. Explain how an address redirect (ICMP) might be useful for mobile devices. What might be the downside of your solution?
9. How could the Record Route option of IP be used in conjuction with source routing?
10. Why does IPv6 rely on source routing rather than the traditional routing methods and why did IPv6 change the fragmentation from the router to the sender. What do these changes mean for the sender of an IP packet?