| Chapter 12 presented the network-communications architecture of FreeBSD. In this chapter, we examine the network protocols implemented within this framework. The FreeBSD system supports several major communication domains including IPv4, IPv6, Xerox Network Systems (NS), ISO/OSI, and the local domain (formerly known as the UNIX domain). The local domain does not include network protocols because it operates entirely within a single system. The IPv4 protocol suite was the first set of protocols implemented within the network architecture of 4.2BSD. Following the release of 4.2BSD, several proprietary protocol families were implemented by vendors within the network architecture. However, it was not until the addition of the Xerox NS protocols in 4.3BSD that the system's ability to support multiple network-protocol families was visibly demonstrated. Although some parts of the protocol interface were previously unused and thus unimplemented, the changes required to add a second network-protocol family did not substantially modify the network architecture. The implementation of the ISO/OSI networking protocols, as well as other changing requirements, led to a further refinement of the network architecture in 4.4BSD. Two new protocols that were added to the system, IPv6 and IPSec, required several changes because of its need to coexist simultaneously with IPv4. Those changes, as well as IPv6 and IPSec, are presented at the end of this chapter. In this chapter, we concentrate on the organization and implementation of the IPv4 protocols. This protocol implementation is the standard on which the current Internet is built because it was publicly available when many vendors were looking for tuned and reliable communication protocols. Throughout this chapter we use Internet and IPv4 interchangeably. Specific mention will be made when talking about the new IPv6 protocols, which are meant to eventually supplant IPv4. After describing the overall architecture of the IPv4 protocols, we shall examine their operation according to the structure defined in Chapter 12. We shall also describe the significant algorithms used by the protocols within IPv4. We then shall discuss changes that the developers made in the system motivated by aspects of the IPv6 protocols and their implementation. |
