Hello ladies and gentlemen, today I am starting a new chapter! This one is called TCP/IP Applications, and I will start rushing. So hold on tight, cause there will be no more specificities, now I'm all-in. Let's go!
Now, TCP/IP is extremely broad since there are hundreds of terms that go into it (Ex: UDP, ICMP, HTTP, DHCP, POP), but it's the simplest way of establishing the protocol as a whole. Imagine that you were having a friendly conversation with someone, in networking that's known as connection-oriented communication. Any communication between a computer and another is called a "session". For example, when you open a webpage, a session has started. Transmission Control Protocol (TCP) enables this type of connection-oriented communication, and it also happens to be the most popular session type on the average TCP/IP network. As is obvious there is the server which hosts the webpage, while the client has the web browser. When you enter a web page ,the client sends a SYN (synchronize) packet to the web server. The server will return it, if it does indeed receive it, while also sending an ACK (acknowledgement) packet. Then the Client will send an ACK to the server. This is known as a TCP "three-way handshake". When the server finished sending the web page, it will send a FIN, ACK (finished, acknowledgment) packet. Client responds with an ACK packet with its own FIN, ACK packet. Then both the client and server will consider the session closed.
Most TCP/IP applications will use TCP because despite the fact that some packets will not reach the destination, the computer receiving will just ask for a repeat to receive it. The User Datagram Protocol (UDP) is used a lot, but not as much as TCP by a mile. It's great for sessions that don't require connection-oriented things. Then there's Dynamic Host Configuration Protocol (DHCP) and heck, we already know what that is. This is an example of an application which uses UDP. Every DHCP session will just send information without confirmation. It uses two port numbers, 67 and 68 for sending data to DHCP clients. More examples, there's NTP/STNP which are also popular applications which happen to use UDP. they stand for Network Time Protocol (NTP) and the lightweight version Simple Network Time Protocol (SNTP). Those protocols will sync the clocks of devices on a network to the right time. It uses port 123. Then there's Trivial File Transfer Protocol (TFTP) which enables file transfers from one machine to another. This is a critical data transfer, which shows that UDP can be used for such things as well. However, TFTP using UDP doesn't have data protection, so across the Internet you wouldn't use it.
We know that TCP and UDP have extreme differences, one being connection-oriented, the other not. However, both will modify and manage packets with a destination IP and port numbers, as well as source IP and port numbers. Although a session could have one packet or several take place during the transfer, sometimes applications are so simple they're always connectionless and don't need more than one packet. Ping is one way that you can see ICMP in action. It sends a single ICMP packet called an "echo request" to the IP address you want to send it to. All computers with TCP/IP will respond to those requests with an "echo reply".
Back in Chapter 7 there was talk of IP multi-cast addresses. The challenge of doing such a thing is to determine who wants the multi-cast and who doesn't. The Internet Group Management Protocol (IGMP) enables routers to communicate with hosts to determine a group membership, as my textbook puts it. Also, multi-cast is in the Class D range, meaning it uses a small subnet of the Class D range. Those who want multi-cast must tell their router or switch they want it. To do that, they have to join the IGMP group. This ends my entry for today, more to come tomorrow! Thanks for reading, and goodbye.
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