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Hey everyone and welcome back. Now what I want to do is to briefly shift gears and talk about FTP.

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This is the file transfer protocol and as you may guess the actual name is pretty descriptive of

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its function. This is used for the transferring of files and it is still very very popular in

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modern networks so it definitely is worthwhile for us to understand this and be aware of it,

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not just for the purposes of the examination but also as Linux engineers. So let's talk about

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how the actual connection of FTP actually operates then. So what I'll do here is if we can imagine

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we have an FTP server, we'll say FTP and we can also have a client. So this could just be someone

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on their computer looking to receive some type of files. Now one thing to note is that FTP is going

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to rely heavily on two ports. The first port is going to be port number 20 and the second one is

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going to be port number 21. Now these two ports ultimately serve slightly different purposes.

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They both use or are both used for FTP should I say. Port 20 is going to be the actual transferring

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of data is going to be sent over this port whereas port 21. This is going to be used to control or

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handle the connection itself. What does this actually mean? Well if we actually dive in and

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look at an example of how a connection can be initiated hopefully this will make a little bit

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more sense. So check this out we've got this client over here. Now the client is going to request

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some type of file from the FTP server over here. Now what's got to happen first is that this client

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over here has got to specify a source port number of its own. Now this can be a random port number.

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If I just happen to specify 9594 let's just say random number and actually let's just give each

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one an IP address. Let's imagine this is 10112 and this can be 10111. So what the client is going

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to do is going to make a connection to FTP. Pretty much saying hey my IP address is 10112.

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I am starting a connection over my local port of 9594. This is a random port chosen by the clients.

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Now the crucial thing is that this actual request is going to be sent to the server on its IP address

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using port 21 which is an FTP port but remember this is the port used to control or handle the

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connection. So this is not where the data is going to actually come across. This is just to

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instantiate this connection. Now in this connection the client is going to communicate another

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port number different from this source one right here. Again it will be a random one let's just say

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9595 so one higher but ultimately what the client is doing here is saying hey I want FTP services

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from you as indicated by the port from this server and when you respond to me I want you to send data

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to me on my IP address up here on this particular port in this case 9595. Now the crucial thing

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is that when FTP responds and actually sends the data to this IP address to this particular port

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the FTP service is going to open up here but it's going to open up locally on port 20 on FTP because

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now we're actually sending over the data the actual file that was requested. So this is the big

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difference port 21 used to open up and instantiate the connection when the data is actually flowing

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it's going to be over port 20 again this is from the server's point of view. The client can just

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use random ports as long as it's communicating those ports to the server. Now this type of

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connection here is a very particular type of FTP connection this is known as active FTP. Now the

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issues with active FTP is simply due to what we just recently talked about and that is with respect

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to firewalls because firewalls don't happen to like inbound connections or at least unless you

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have to explicitly open inbound connections which is kind of frowned upon not really desirable.

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So think about this imagine the same connection we've got the client over here we have the FTP

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server think about what actually happened here we've got our port of 9594 I believe it was we

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send the request to the FTP server on port 20. FTP server uses port 21 to respond back to us but FTP

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opens a fresh connection into our computer as the client this time on port 9595 now because this is an

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inbound connection from the perspective of the client uninitiated by the client i.e it was initiated

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by a remote server firewall operators on the client side may not be too keen with the ability of an

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external source to just open a connection directly into the network or into the host so because of

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this FTP active can become problematic so the way this is resolved is by using FTP in passive mode

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now this is handled a little bit differently yet again so let me show you how this works

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so over here on the client side once again and we will have the server FTP things are going to look

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a little bit different but you will recognize a lot of the steps here so check this out imagine

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that the client here wants those FTP services so once again let's just say 9495 I believe the

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port is it doesn't actually matter let's just say it's 9495 this time the client is going to send a

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request to FTP on port 21 saying pretty much hey master FTP I need to have a passive connection

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so FTP receives this on its control port of port 21 and what FTP is going to do it's going to respond

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back pretty much saying okay I'm going to facilitate this connection by waiting for you I'm going to

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open up a random port on my side of the connection and you can call in to me that way the client can

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be the one initiating the connection in fact I've accidentally rubbed out that five there let me just

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draw that back so like I say FTP is going to say okay I'm going to wait for you and FTP is now going

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to be the one that will choose a random port so let's just say FTP chooses 8642 whatever it may be

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and it communicates that information to the client so now the client is going to use a new port once

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again so the client could use 9496 to make an outbound connection and it's going to make an

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outbound connection to the FTP server on its IP address but it's going to target this particular

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port that was specified by the FTP server but again the crucial difference here is that this is an

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outbound connection initiated by the client so the client is only ever doing outbound initiation

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it's never waiting for a connection to come inbound and this is going to solve these particular

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firewall issues so once the connection is now open this channel is open effectively and FTP

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can begin sending all of that FTP data through this channel and the client can receive all of that

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via FTP so now that we understand the two different modes of connecting to FTP what we now want to

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look at are some FTP server options that we can use if we want to actually supply these services

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ourselves now we do have a few options the first one and the main focal point I would say is one

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called VSFTPD this is the very secure FTP daemon now VSFTPD is a very good daemon although I would

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be hesitant or wary of any software which happens to be very secure that's just my own personal

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bias but yeah it's good software but please don't put too much faith in the system sometimes the

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names can be deceiving the next one we want to look at is one called pure FTPD and the last one

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is one called pro FTPD now really like I say the main one we want to focus on is VSFTPD the big

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crucial thing we have to know here is that this is actually controlled like so much of what we see

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on linux directly via configuration files whereas if we use pure FTPD we do not modify

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configuration files instead we make all the changes to the service directly via the command line

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now with respect to pro FTPD honestly I really wouldn't worry about looking into this with any

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great detail the exam objectives really just specify that we have an awareness of pro FTP's

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existence so that you do recognize it is an FTP developer option but really like I say let's turn

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our attention to VSFTPD and begin a little installation then so what I will do is I will

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clear the screen so what I'm going to say here is sudo apt install and I will say VSFTPD to install

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VSFTPD I will type in my password here and hit enter would be super helpful if I could type the

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right password of course so try again there we go now the installation begins now depending on the

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distribution that you're using VSFTPD may be located in two different locations or rather

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should I say the configuration file for VSFTPD the first location you should check would be in the

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Etsy directory and then you will either have a VSFTPD directory and inside that directory you

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would have a file called VSFTPD.conf however if you are like me you actually will not have this

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particular directory and instead the VSFTPD configuration file will be directly within the

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Etsy directory so if I just say sudo nano and do VSFTPD.conf if I hit enter this here is the main

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configuration file now there are some settings we want to be aware of for example if I scroll down

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here we have this setting for anonymous underscore enable this is set to the value no this means that

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anonymous logins are disabled by default what this means is that we're not going to allow anyone to

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log in to our ftp server instead they must provide credentials such as a username and a valid password

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in order to access our services now just below this we also have local underscore enable set to

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the value yes this is going to allow us to allow local users to log in so local users with their

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local credentials they can ultimately access the services on the file transfer protocol server

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with this configuration enabled now below here we have write enabled equals yes this is commented out

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meaning that the actual configuration is not taking effect this means that they cannot actually make

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write changes to the ftp server meaning that they can't actually modify the contents on the server

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similar to what we saw before we have this configuration file here or rather this configuration

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setting should I say a non upload enable yes if we actually uncomment this it's going to allow

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anonymous users who have logged in without providing credentials to actually upload files to the server

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itself naturally this can obviously be very dangerous if you don't have a good grip of who can

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actually access your server so naturally what I want to do is to actually comment this so that

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this configuration does not take effect and if we scroll on down we're going to see more and more

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settings you can explore these at your leisure but really those are the main configurations that we

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want to be concerned about so for now what I will do here is I will just escape this by pressing control

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x and just say no here and now what I will do is I will just access my machine right here over ftp

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now I'll just say ftp localhost if I hit enter so if I say the name happens to be ipv0 and I type

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an ipv0 password right here and hit enter we can see here the login is successful and we actually

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now have this ftp prompt if I just say help we can actually see all of the commands that are available

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to us over ftp so I can do things like ls to see a listing of the files I could cd into a directory

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such as documents and do an ls notice nothing is within this particular directory and if I happen

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to have right access I could write to this directory and host files within this server

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accessible via ftp now like I say if I happen to just say quit to quit the connection if I try to log

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in again and I happen to say anonymous and I just specify the password as anonymous the actual

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connection is going to fail however if I say quit go back into my configuration file if I go on down

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I will change this to the value yes and I'll save the changes right here and escape out so now what

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I can do is I can actually restart the service by saying pseudo service vs fdpd and restart that is

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now restarted if I do ftp localhost and I just use the username of anonymous and the password again

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of anonymous now this time the login is deemed successful so really with respect to ftp we want

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to understand the nature of the connection are we using an active connection or a passive connection

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when would you use one or the other the common ports are going to be in use port 21 and port 20

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we want to understand some of the options that we have to host a ftp server such as vs fdpd which

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will be managed by a configuration file such as the ones we just saw and we also have pure ftpd

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which is a command line option as well as pro fdpd whereby we really just have to have a general

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awareness of its existence as an ftp server okay doc so that is us for ftp I hope this has been

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informative for you and I'd like to thank you for viewing