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in our previous video we talked about
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how services have port numbers that they
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use so that other devices can
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communicate and use those services we
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refer to these as well-known port
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numbers because both the server and the
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client need to know exactly what port
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number they'll use to communicate this
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is not only important for the server and
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the client but it's also important for
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any firewalls that may be in the middle
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of that communication firewalls have to
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decide whether to allow or disallow this
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traffic and they often make that
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decision based on the port number as we
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go through this video you'll see that
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there are a lot of different port
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numbers that you should use and if
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you've never worked with port numbers
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before this will seem like rote
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memorization but the port numbers
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themselves become easier and easier to
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remember as you continue to use them
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it's important to know these port
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numbers and what protocols are often
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used by a particular port number but
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it's also important to know when you
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would use these protocols for example
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your exam might ask you what port number
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is used by an application that transfers
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data in a particular way across the
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network
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let's start our conversation of port
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numbers with ftp or the file transfer
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protocol as the name implies this is a
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protocol that transfers files from one
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device to another there are two port
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numbers used by ftp one is tcp port 20
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this is for data transfers and tcp port
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21 which is used to control the data
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transfer ftp is a generic way to
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transfer data between devices but it
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commonly requires some type of
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authentication to log into that remote
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device so you might use a username and
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password although some systems will
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allow you to log in as anonymous and use
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any password to gain access the ftp
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protocol also includes a number of file
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management functions so when you connect
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to an ftp server you can list all of the
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files on that server you can add delete
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rename and perform other file management
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functions all by using ftp
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there may be times when you need to
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connect to a remote device through a
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terminal or command line front end it's
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common to use secure shell or ssh to
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provide this terminal connection to a
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remote device ssh commonly communicates
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over tcp using port 22 and it has this
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text-based front-end to be able to
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access that remote device although we
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see plain text on our screen any
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communication sent over the network is
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sent as encrypted data that's where the
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secure comes from in the name secure
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shell
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there's another way to connect to a
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remote device using this text-based or
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console front-end and it's using telnet
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or the telecommunication network
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protocol telnet commonly uses tcp port
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23 to provide this connection just like
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ssh telnet provides this text-based
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front-end that allows us to connect to
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the remote console of another device
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but unlike ssh all of the communication
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between this telnet front-end and the
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telnet server is all sent in the clear
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or non-encrypted this means that anyone
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who might be capturing packets between
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these two devices will see everything
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that you're sending over this link
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including usernames passwords and
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everything else this is why we often say
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that you shouldn't use telnet on your
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production networks and instead you
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should always use ssh for terminal
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communication
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there are probably millions of email
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servers that are located on the internet
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and the protocol that those email server
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use to communicate with each other is
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the simple mail transfer protocol or
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smtp smtp commonly uses tcp using port
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25. not only is smtp used to communicate
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between mail servers but it's also used
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for our mail clients to send mail to a
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mail server so if you're using a mail
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client on your mobile device or your
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desktop computer and you're sending an
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email message you could be using smtp
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although it's common to use smtp to send
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mail receiving mail is done using a
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completely different set of protocols so
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if you were to look at your email client
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you're probably using imap or pop3 to be
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able to receive mail and smtp to be able
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to send mail
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if you need to connect to a remote
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website you would probably type into
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your browser
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www.professormesser.com and hit enter
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behind the scenes your system needs to
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be able to communicate with the
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professor messer web server but it has
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no idea what the ip address is for that
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server to be able to resolve an ip
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address from that fully qualified domain
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name your system will use dns or the
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domain name system dns commonly uses udp
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port 53 to be able to make this
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connection between you and the dns
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server these are obviously very critical
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resources because we don't often
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memorize ip addresses of servers and
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very often server ip addresses can
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change without any type of notification
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it's dns that provides that resolution
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between a name that we're typing in on
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the browser and the ip address that will
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be used for the actual communication
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if you've ever used your mobile device
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on the wi-fi network of a coffee shop
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then you've automatically received an ip
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address that you can use on that network
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this ip address was assigned
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automatically using the dynamic host
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configuration protocol or dhcp the
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well-known ports for dhcp are udp port
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67 and udp port 68. of course you need a
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dhcp server to assign these ip addresses
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to devices on your network that
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functionality is commonly built into the
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routers and wireless access points that
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we use these days this dhcp server will
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have a large pool of ip addresses that
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can then be assigned to devices on your
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network all of these ip addresses are
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assigned in real time so when you start
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up your computer it queries the dhcp
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server and the dhcp server assigns your
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device all of your ip configuration
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details
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dhcp uses a leasing system to assign
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these ip addresses so you are only using
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this ip address for a certain amount of
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time and after that lease expires and
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you're no longer on the network that ip
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address goes back in the pool for
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someone else to use
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network administrators can also
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configure dhcp servers to always assign
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the same ip address to certain devices
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so if there are routers firewalls
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switches and other infrastructure
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devices on your network your network
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administrator may configure dhcp
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reservations so those devices always
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receive the same ip address every time
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they're booted up this also means that
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if you need to change any of the ip
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configurations on these devices you
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don't have to go to the devices to make
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those changes you simply make them on
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the dhcp server the next time that
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device requests a dhcp address it will
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receive the new configuration
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if you've ever used a web browser then
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you've used http and https http is the
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hypertext transfer protocol and this is
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the common protocol used by our browsers
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to communicate to web servers there are
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two different protocols depending on the
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type of communication that you'll be
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doing if you're communicating in the
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clear or in a non-encrypted form you
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would be using the http protocol which
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uses tcp and port 80. if your browser's
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communicating over an encrypted
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connection then it's probably using
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https the s being for secure and that
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uses tcp port 443.
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we mentioned earlier that sending email
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messages can use smtp or the simple mail
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transfer protocol but to receive email
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messages you would commonly use pop3 or
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imap pop3 is the post office protocol
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version 3 and it commonly uses tcp port
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110 pop3 was designed to retrieve email
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messages to an email client but it
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wasn't built for multiple email clients
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and of course these days we tend to walk
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around with many different mobile
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devices all accessing the same email
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inbox to be able to synchronize across
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all of these different mailboxes we
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commonly use imap4 or the internet
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message access protocol version 4. imap
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commonly uses tcp port 143 to be able to
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download and manage that mailbox
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many operating systems have their own
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method of transferring files and
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information between devices using that
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operating system windows commonly uses
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server message block or smb to be able
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to provide this connection this is the
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protocol commonly used by microsoft
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windows so if you're transferring files
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between devices or you're sending a
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print job to a printer it's probably
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using smb you might also hear smb
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referenced as cifs or the common
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internet file system smb uses a number
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of different protocols to be able to
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communicate and if you're communicating
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to an older windows machine you're
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probably using netbios over tcp netbios
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is the network basic input output system
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this uses udp port 137 as a name service
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function so that it can find devices on
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your network by the name and uses tcp
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port 139 to set up a session and
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transfer data between devices
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on most modern versions of windows
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netbios isn't used devices can
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communicate directly between each other
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using tcpip in those cases it would use
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a direct smb connection using tcp port
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445. this allows us to have a direct s b
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communication between two devices by
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using only tcp
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if you plan on doing any work as a
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network administrator you'll become very
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familiar with snmp or the simple network
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management protocol snmp allows a
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network management device to query these
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infrastructure devices for performance
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details and receive those metrics in
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return this uses udp port 161 to perform
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these queries you can also configure the
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infrastructure device to monitor for
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certain metrics and if it exceeds any of
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those metrics it can send an alert to
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the management station we refer to these
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alerts as traps and the traps use udp
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port 162.
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if you're configuring snmp on a device
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it will ask you if you're using version
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one version two or version three version
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one was obviously the original snmp
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version it sent structured information
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across the network but all of this
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information was sent in the clear or in
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a non-encrypted form we introduced a
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newer version of snmp with snmp version
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2 which allowed us to do bulk transfers
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of information but still all of that
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information was being sent in a
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non-encrypted form to be able to include
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additional security with snmp you need
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to use snmp v3 this includes encryption
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that allows us to have message integrity
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authentication and encryption of all of
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the snmp data
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we use directories extensively on our
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modern networks and one very common
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protocol to use to query these
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directories is ldap ldap is the
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lightweight directory access protocol
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and it commonly uses tcp port 389. there
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are many implementations of ldap but one
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of the most popular is microsoft active
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directory which allows you to query that
00:11:05
active directory server using the ldap
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protocol
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if you've ever worked in a support role
00:11:12
or on a help desk then you've probably
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performed some type of remote access to
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someone's desktop one very popular
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protocol to provide this remote
00:11:20
communication is rdp or the remote
00:11:23
desktop protocol this is the standard
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protocol used by windows for the remote
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sharing and it commonly uses tcp port
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3389
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these remote desktop services are
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available in many different editions of
00:11:36
windows and if you're using windows
00:11:38
today then you probably have built into
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the operating system the ability to
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connect to or receive a remote desktop
00:11:45
session
00:11:46
rdp can be used to take over and control
00:11:48
an entire system or just to run a single
00:11:51
application from that server although
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you'll find servers running rdp almost
00:11:56
exclusively on windows there are clients
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that you can run on almost any operating
00:12:01
system so if you're running linux macos
00:12:04
android or any other operating system
00:12:06
there's probably an application you can
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load that will allow you to connect to a
00:12:10
windows device using the remote desktop
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protocol
