CompTIA A+ Network Port Numbers: TCP/UDP Protocols Explained

as we've discussed in a previous video the port numbers used by TCP and UDP can be very important when trying to

communicate to a service so it's useful to know what those port numbers are if you're trying to troubleshoot any type

of communications issue we might also need to know these port numbers if we're performing some type of firewall

configuration our firewalls often use TCP and UDP port numbers as one of the criteria that it uses to allow or to

block Lo Network traffic as you go through this video you'll find there are a number of port numbers that you're

required to know as part of your A+ studies you'll find that memorizing these port numbers can sometimes feel a

bit tedious but after you start using these applications configuring firewalls and troubleshooting network

communication you'll find that most of these port numbers become second nature for the purposes of your A+ studies make

sure that you understand not only the port number and the protocol associated with it but that you understand why that

particular protocol is important and how it's used on the network the first port numbers we'll

look at are port numbers TCP Port 20 and TCP Port 21 these two port numbers are commonly associated with FTP or the file

transfer protocol FTP is a generic file transfer protocol that could be used by many different operating systems to

transfer information from one device to another and different types of FTP may use one or both of these prot protocols

TCP Port 20 is often used as the active data transfer and Port 21 is often used as the administration or control Port

the FTP protocol often requires you to have some type of authentication into this system so it may ask for a username

a password or some other type of authentication Factor FTP can also be configured with an anonymous or generic

login so that anyone can log in regardless of what the username or password might be FTP is also a

full-featured protocol that not only can transfer a file but can list the files available in a particular directory we

can add delete change the file name and perform other Administration functions as

well as part of our tasks as server administrators or network administrators we are often required to connect to our

Remote device and make configuration changes at the command line to be able to do this securely across the network

we need to use a protocol that can encrypt all of this data as we're sending it from one side to the other

the most common protocol used for this function is SSH or secure shell it provides an encrypted communication link

over TCP Port 22 this is very similar to the old style tnet protocol but tnet is one that we commonly no longer see in

use because it does not provide any type of encryption if you're communicating at the command line to a server you should

always be using SSH and you'll find that it almost always is using TCP Port 22 however you may find that there is a

system in your network that is very old that does not support SSH and the only way to administer that device at the

command line is using the older tnet protocol telnet stands for telecommunications Network and it

commonly communicates over TCP Port 23 visually and functionally this works identical to SSH you have a command line

you can log into a device with your username and password you can administer that device remotely but the major

difference is that all of the communication used for tnet is in the clear there's no encryption used for

tnet and that's why most organizations will prevent anyone from using the tnet protocol and instead recommend that you

use SSH to perform this communication email continues to be one of the most popular forms of

communication across our networks and to be able to facilitate that communication we need some type of protocol that can

send mail from one server to another that protocol is the simple mail transfer protocol or SMTP SMTP commonly

uses TCP Port 25 to be able to send these email messages from one email server to another you may also find that

some devices are configured to send information to the email server initially also using this SMTP protocol

so not only are you configuring this on your mail server you may also o find that you're configuring SMTP with the

appropriate port number on your local device to be able to receive email messages we would commonly use protocols

such as IMAP or pop 3 and we'll talk about those protocols and their Associated port numbers later in this

video in these videos so far we've talked a lot about devices able to communicate with each other using IP or

Internet Protocol the Internet Protocol address is one very similar to what you would see here one 62.1 159 2461 164 but

when we're typing things into our browser we're not typing in a bunch of numbers we're typing in the name of a

website such as www.professormesser.com in order to translate this fully

qualified domain name into a usable IP address for network communication we need to perform a translation using the

domain name system or DNS DNS commonly uses UDP Port 53 as you can imagine DNS is a very popular

and important service because we almost never memorize IP addresses to be able to communicate to these devices but it's

very common to remember the fully qualified domain name for that reason it's very common to have multiple DNS

servers for redundancy so that we are always able to resolve the fully qualified domain name to the appropriate

IP address the computer on your network was probably not manually configured with a

set of IP addresses subnet masks default gateways or DNS servers this was done automatically when you turn your

computer on using the dynamic host configuration protocol or DHCP DHCP happens automatically behind

the scenes and it makes the entire process of configuring your system with these addresses completely seamless DHCP

commonly uses UDP Port 67 and UDP Port 68 on your network is a DHCP service that may be on a standalone server or

Appliance or may be integrated into a small office home office wireless router that you might have at home on this

server is a pool of available IP addresses and when a device connects to the network it requests an IP address

and configuration parameters from that pool when a device starts up it receives that IP address and it leases that IP

address for a certain amount of time when that lease is up it can choose to renew the lease or give the IP address

back and put it into the pool for someone else to use system administrators can also use DHCP to

manually configure IP addresses that will always be assigned to particular devices so if you have a printer or

server that you would like to always have the same IP address you can reserve that IP address in your DHCP server and

it will be automatically assigned with the same IP address every time that printer or server starts

up you're probably watching this video in a browser and to be able to perform that functionality you're probably using

HTT TP or https this is the hypertext transfer protocol or hypertext transfer protocol secure the standard form of

HTTP sends all of the HTTP data over a non-encrypted or in the clear communication and it often uses TCP Port

80 if you see any traffic using TCP Port 443 it's probably using the secure version of HTTP which means that all of

that web communication inside of that packet will be encrypted a large percentage of the devices you

communicate to in your browser are probably going to use https these days but you'll still find a number of web

services that are not using the encrypted version and instead are sending all of their traffic via TCP

Port 80 and the HTTP protocol if you're using an email client on your computer or your mobile device

you may be receiving emails using a number of different protocols two of the more popular Protocols are POP 3 and

IMAP POP 3 is the post office protocol version three and it commonly uses TCP Port 110 to be able to transfer data

down to your computer a newer and somewhat more functional protocol for receiving email is IMAP 4 or the

internet message access protocol version 4 IMAP commonly uses TCP Port 143 IMAP provides a number of additional features

not available in pop 3 such as the management of the inbox from multiple clients you're able to make make folders

and transfer emails into those folders and all of those updates will be synchronized across all of your

different systems and all of those updates will be synchronized across all of your different email

clients if you're using Microsoft Windows there's a process for transferring data within windows that

uses a protocol named server message block or SMB you may also see this referred to as the common internet file

system or cifs not only is this used for file trans transfers it's used to send information to printer cues and for

other processes where Windows needs to communicate information between different Windows devices older Windows

devices used an additional protocol inside of tcpip called netbios this net bios protocol used two primary port

numbers to be able to communicate UDP Port 137 used a net bios name service which is very similar to the DNS name

service that we talked about earlier and to be able to set up sessions to transfer files it uses TCP Port 139 on

most modern versions of Windows you'll find Direct connectivity between IP addresses that don't use the net bios

protocol we refer to that as direct communication or net bios less communication and it often uses TCP Port

445 most organizations will have a central database that contains all of the important information about the

devices users and and important resources available on their Network this is usually a directory of services

or a database that contains all of this information and to be able to access this database we use a standard set of

protocols one of these protocols is ldap or ldaps this stands for the lightweight directory access protocol or the

lightweight directory access protocol secure ldap commonly uses TCP port 389 this directory is usually separated into

different categories such as an organization an organizational unit or a common name for example at mess Studios

we might have a production organizational unit a support organizational unit and an engineering

organizational unit and of course within those there may be individuals using a common name such as Sam or Daniel and we

might also have a database called Tech docs using ldap we can refer to this database to find where these components

might be and in some cases even provide a additional details such as authentication for any individual users

a very common use of ldap is Microsoft's active directory infrastructure where that database is able to be referenced

using the ldap protocol if you are troubleshooting technology then you're probably very

familiar with remote control access of a separate machine these days we have users around the world and it's not very

practical for you to visit every single one of those users directly to be able to solve problems s on their computer in

those cases we'll probably use some type of remote access protocol such as RDP or remote desktop protocol this allows you

to view and share the desktop on a Remote device using TCP Port 3389 this is primarily used to access

Windows devices and to be able to control those windows devices across the network you can usually do this from a

Windows device itself or from many other operating systems as well you can use RDP to control an entire computer or to

Simply run a single application on that remote computer and although RDP is commonly associated with connecting to

Windows devices there are also many RDP clients that would allow you to connect to that Windows computer from Mac OS

Linux Unix iPhone and other operating systems as well