| 2.1 | Consider a host that supports IP and other networking protocols, such as IPX or AppleTalk. Each of these protocols will have its own stack. Suppose that the protocols all use the same Ethernet interface. Investigate the Ethernet frame format and discover how the operating system is able to tell which stack it should deliver the data to. |
| 2.2 | What is the identification number of the IP datagram in Figure 2.4? |
| 2.3 | How can IP differentiate the first fragment of a fragmented IP datagram, which will have a fragment offset of 0, from an unfragmented datagram? |
| 2.4 | IP does not reassemble a fragmented datagram until it has received all the fragments. How does IP know when it has received all the fragments? Remember that the fragments can arrive out of order. |
| 2.5 | We said that UDP checksums are optional and that a sender signals the receiver that it is not using a checksum by setting the checksum field in the UDP header to 0. How can a receiver tell the difference between "no checksum" and a UDP datagram that happens to checksum to 0? Hint: Internet checksums are calculated using ones-complement arithmetic. |
| 2.6 | Ignoring any implementation-specific or MTU restrictions, what is the maximum amount of data that can be transmitted in a UDP datagram? |
| 2.7 | Suppose that hosts A and B have established a TCP connection but are not exchanging data, and that host A crashes and reboots. Is there still a connection? Do hosts A and B agree with your answer? |
| 2.8 | What will the routing table for host 4 of Figure 2.9 look like? |
| 2.9 | We said that only the hop-by-hop extension header in IPv6 needs to be examined by each router. Why doesn't the routing header need to be examined by each router also? |
| 2.10 | How do the IGP distance-vector protocols differ from the BGP path-vector protocol? |
| 2.11 | BGP views the Internet abstractly as a graph, with the nodes being autonomous systems. This suggests that a link-state protocol might be an appropriate way of introducing more precise metrics into EGP routing. What problems do you think a link-state protocol might encounter? |
| 2.12 | As with any other routing protocol, BGP must take steps to ensure that routing loops do not develop. How can BGP use the path information associated with an advertised network to avoid such loops? |
