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CHAPTER 21
Network Layer: Address Mapping,
Error Reporting, and Multiplexing
Solutions to Odd-Numbered Review Questions and Exercises
Review Questions
1. The size of an ARP packet is variable, depending on the length of the logical and
physical addresses used.
3. The size of the ARP packet in Question 2 is 28 bytes. We need to pad the data to
have the minimum size of 46. The size of the packet in the Ethernet frame is then
calculated as 6 + 6 + 2 + 46 + 4 = 64 bytes (without preamble and SFD).
5. This restriction prevents ICMP packets from flooding the network. Without this
restriction an endless flow of ICMP packets could be created.
7. A host would never receive a redirection message if there is only one router that
connects the local network to the outside world.
9. The minimum size of an IP packet that carries an ICMP packet would be 28 bytes
(a 20 byte IP header + an 8 byte router solicitation packet). The maximum size
would be 2068 bytes (a 20 byte IP header + a 2048 byte router advertisement
packet).
11. The minimum size would be 64 bytes if we do not consider the preamble and SFD
fields, which are added at the physical layer. The maximum size would be 1518
bytes, again not considering the preamble and SFD fields. Although the maximum
size of an ICMP packet can be much more than 1500 bytes (for a router advertise-
ment packet), Ethernet can carry only 1500 bytes of it.
Exercises
13. See Figure 21.1. Note that all values are in hexadecimal. Note also that the hard-
ware addresses does not fit in the 4-byte word boundaries. We have also shown the
IP address in parentheses.
15. See Figure 21.2. We have not shown the preamble and SFD fields, which are
added in the physical layer.
17. It could happen that host B is unreachable, for some reason. The error message
generated by an intermediate router could then be lost on its way back to host A.
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