At the top of the TCP/IP protocol architecture is the Application Layer. This layer includes all processes that use the Transport Layer protocols to deliver data. There are many applications protocols. Most provide user services, and new services are always being added to this layer. Some widely known and implemented applications protocols are:[4]
While HTTP, FTP, and SMTP are important TCP/IP applications, you will work with many others as both a user and a system administrator. Some other commonly used TCP/IP applications are:
- Domain Name System (DNS)
Also called name service, this application maps IP addresses to the names assigned to network devices. DNS is discussed in detail in Chapter 8.
- Open Shortest Path First (OSPF)
Routing is central to the way TCP/IP works. OSPF, which is described in Appendix D, is used by network devices to exchange routing information. Routing is discussed in Chapter 2, and Chapter 9.
- Dynamic Host Configuration Protocol (DHCP)
This protocol allows networked computers to be automatically configured from a central server. The DHCP server is covered in Chapter 6.
Some protocols, such as FTP, can only be used if the user has some knowledge of the network. Other protocols, like OSPF, run without the user even knowing that they exist. As system administrator, you are aware of all these applications and all the protocols in the other TCP/IP layers. And you’re responsible for configuring them!
[4] These applications are all part of the Internet Information Server (IIS) software covered in Chapter 10.
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