Popular TCP/IP Applications
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Throughout your preparation for the CCNA Routing and Switching exams, you will come
across a variety of TCP/IP applications. You should at least be aware of some of the applications
that can be used to help manage and control a network.
The World Wide Web (WWW) application exists through web browsers accessing the content
available on web servers. Although it is often thought of as an end-user application, you
can actually use WWW to manage a router or switch. You enable a web server function in
the router or switch and use a browser to access the router or switch.
The Domain Name System (DNS) allows users to use names to refer to computers, with DNS
being used to find the corresponding IP addresses. DNS also uses a client/server model, with
DNS servers being controlled by networking personnel and DNS client functions being part
of most any device that uses TCP/IP today. The client simply asks the DNS server to supply
the IP address that corresponds to a given name.
Simple Network Management Protocol (SNMP) is an application layer protocol used specifically
for network device management. For example, Cisco supplies a large variety of network
management products, many of them in the Cisco Prime network management software
product family. They can be used to query, compile, store, and display information about
a network’s operation. To query the network devices, Cisco Prime software mainly uses
Traditionally, to move files to and from a router or switch, Cisco used Trivial File Transfer
Protocol (TFTP) . TFTP defines a protocol for basic file transfer—hence the word trivial.
Alternatively, routers and switches can use File Transfer Protocol (FTP), which is a much
more functional protocol, to transfer files. Both work well for moving files into and out
of Cisco devices. FTP allows many more features, making it a good choice for the general
end-user population. TFTP client and server applications are very simple, making them good
tools as embedded parts of networking devices.
Some of these applications use TCP, and some use UDP. For example, Simple Mail Transfer
Protocol (SMTP) and Post Office Protocol version 3 (POP3), both used for transferring
mail, require guaranteed delivery, so they use TCP.
Regardless of which transport layer protocol is used, applications use a well-known port
number so that clients know which port to attempt to connect to. Table 5-3 lists several
popular applications and their well-known port numbers.
1 DNS uses both UDP and TCP in different instances. It uses port 53 for both TCP and UDP.