Common TCP/UDP applications
FTP and TFTP
FTP stands for File Transfer Protocol. FTP is a programs that allows the user to send and retrieve files. Although FTP is a protocol, it is also itself a application. FTP allows different types of directory operations, even allowing users to move between directories and copy files. FTP supports authentication of users allowing administrators some security. FTP also allows administrators to define what users are capable of doing. The administrator can create groups of users, some may be allowed to modify files as well as copy them, while others may only be allowed to copy files.
TFTP stands for Trivial File Transfer Protocol. TFTP is actually a UDP protocol making it an unreliable connectionless protocol. TFTP gives you the basis functions of FTP, such as file transfers, without any added functions such as authentication. TFTP does not allow any directory operations, you must know where your file is. TFTP's only function is to send and receive files.
TFTP stands for Trivial File Transfer Protocol. TFTP is actually a UDP protocol making it an unreliable connectionless protocol. TFTP gives you the basis functions of FTP, such as file transfers, without any added functions such as authentication. TFTP does not allow any directory operations, you must know where your file is. TFTP's only function is to send and receive files.
Telnet
Telnet is a terminal emulation protocol that allows users to access resources on another machine. Telnet actually makes the receiving host think that it is directly connected to a terminal on its local network allowing the user access to its resources. Telnet can be used for a variety of things including telnetting in a remote route to access the Cisco IOS CLI.
Simple Mail Tranfer Protocol
Simple Mail Transfer Protocol is method of email delivery. When SMTP sends and email to a destination the message it tells the receiver of the parameters of the session and then goes through a three command/reply sequence. The first command is the MAIL command that establishes a return address, the next command is the RCPT command that establishes a recipient of the message, and the third command is the DATA command that sends the message text. SMTP is a delivery protocol only POP and IMAP are used for retrieving messages.
Post Office Protocol
Post Office Protocol allows us to receive and store incoming messages. POP3 is the latest version of POP and it allows a user to connect to the POP server and download all the messages waiting for them. The user cannot download emails individually, they must download every message waiting for that user. Once the files are downloaded they may be viewed and manipulated on the local machine without accessing the POP server.
Internet Message Access Protocol
Internet Message Access Protocol allows more control over how you download your emails. IMAP4 gives the user the ability to view the message header or download just part of an email allowing you to see some of the contents without downloading the entire thing. IMAP also adds security with its authentication features.
Simple Network Management Protocol
Simple Network Management Protocol gives users access to network information. SNMP works as a centralized management station that gathers information from network devices and allows the user to view and manipulate this information. SNMP is an invaluable tool to network engineers and administrators as it allows the constant monitoring of network and alerts them when pre defined events occur such as network congestion or packet loss.
Domain Name Service
Domain Name Service is a protocol that resolves host names to IP address. For example if a host were to access this website, www.network-helper.com, the first thing the hosts computer would do is send a query to the DNS server asking it for the IP address of the domain name www.network-helper.com. The DNS would respond with the appropriate IP address and the host would use that address to communicate with the website.
Hypertext Transfer Protocol
Hyptertext Trasfer Protocol is the protocol that runs web traffic. HTTP manages communications between a web browser and the web server allowing a web browser to access resources on the server.
Hypertext Transfer Protocol Secure
Hypertext Transfer Protocol Secure is HTTP with the added security of SSL. HTTPS simply provides security on top of your HTTP protocol, this allows for encrypted traffic, and authentication.
Network Time Protocol
Network Time Protocol synchronizes the time on all devices in a network. NTP is essential in keeping all devices running on the same time, which is important for a number of things. Later on in the CCNP curriculum you will come across certain tasks that require devices to be running on the same type otherwise it could present real problems into your network.
Dynamic Host Configuration Protocol
Dynamic Host Configuration Protocol assigns IP addresses to hosts. When a host runs DHCP the first thing it does is send out a Discovery message, this message is broadcasted at layer 2 and layer 3. The DHCP server will respond with a Offer, which it will unicast back to the host. When the host receives this Offer it broadcasts back a request asking it for the offered IP address and any other information the DHCP has. The server will finish the exchange by sending an Acknowledgment back to host acknowledging that it can use the IP address, the ACK is sent in the form of a unicast.