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Welcome to Jeremy’s IT Lab. This is a free,
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In this video we will cover
FTP, File Transfer Protocol,
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and TFTP, Trivial File Transfer Protocol.
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As the names suggest, both of these protocols are
used to transfer files over a network. They are
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exam topic 4.9, which states that you must be
able to describe the capabilities and function
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of TFTP and FTP in the network. So, make sure
you understand the purpose of these protocols,
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and make sure you know the differences between
them, even though their purposes are similar.
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Here’s what we’ll cover in this video.
First up, I’ll introduce the purpose of FTP
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and TFTP. The names tell you what their basic
purpose is, but I’ll give a brief overview. Then
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we’ll compare the two protocols to learn about
their functions and how they are different.
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Then I’ll introduce the various file systems
on Cisco IOS. A basic understanding of how
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files are stored on Cisco devices is important.
Finally, we’ll take a look at how to use FTP and
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TFTP in Cisco IOS. As always, watch until
the end of the video for a bonus practice
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question from Boson Software’s ExSim for
CCNA, the best practice exams for the CCNA.
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Here’s a quick summary of FTP and TFTP. FTP,
which stands for File Transfer Protocol,
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and TFTP, which stands for Trivial File
Transfer Protocol, are both industry
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standard protocols used to transfer files over
a network. They both use a client-server model.
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Clients can use FTP or TFTP to copy
files from an FTP or TFTP server.
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They can also use FTP or TFTP to copy files to a
server. As a network engineer, the most common use
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for FTP and TFTP is in the process of upgrading
the operating system of a network device.
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You can use FTP or TFTP on the device to
download the newer version of IOS and then
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reboot the device with the new IOS image. This is,
of course, not the only use for these protocols.
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They can be used to transfer all kinds of
files between different devices over a network.
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But for this video, we’ll use this example. So,
here’s a sample network. I haven’t included any
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cables or anything, we don’t need any details. So,
on the left is a server at software.cisco.com. The
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network admin will download the new IOS image
from Cisco. Then he will transfer the IOS image
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to a server that is reachable by the device he
is going to update, which in this example is R1
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on the right. Finally, the network admin will
use commands in the CLI of R1 to copy the file
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into the flash memory of R1. The last step after
that is to reboot R1 using the new version of IOS.
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So, later in this video I’ll show you how
to use the CLI of a Cisco device to transfer
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files using FTP and TFTP, and then how to reboot
the device with the new IOS image to update it.
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Okay, now let’s move on to talk about
TFTP, the Trivial File Transfer Protocol.
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TFTP was first standardized in 1981.
This is after FTP, but because TFTP is
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simpler I want to introduce it first. It was
named the ‘trivial’ file transfer protocol
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because it is simple and has only basic
features when compared to FTP. It only
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allows a client to copy a file to or from a
server. Nothing else, just simple file transfers.
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As I said, it was released after FTP, but it’s
not a replacement for FTP. It is just another
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tool to use when a lightweight, simple protocol
is more important than advanced functionality.
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TFTP doesn’t use any authentication,
meaning no usernames and passwords,
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so servers will respond to all TFTP requests.
There’s no username or password to check.
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Also, there is no encryption so all data is
sent in plain text. Because of this lack of
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security, TFTP is best used in a controlled
environment to transfer small files quickly.
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You probably shouldn’t use it to transfer
important files over the Internet, for example.
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TFTP servers listen on UDP port 69. So, when
clients initiate communications with the server,
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they will use UDP port 69 as the destination port.
As you already know, UDP is connectionless and
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doesn’t provide reliability using retransmissions.
However, TFTP actually has similar built-in
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connection and reliability features within
the TFTP protocol itself. Let’s take a look.
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First I’ll introduce how TFTP provides reliability
using acknowledgments and retransmissions. Every
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TFTP data message is acknowledged. So, if the
client is transferring a file to the server,
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the server will send Ack messages,
one for each data message.
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However, if the server is transferring a file
to the client, then the client will send Ack
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messages, one for each data message from the
server. Timers are used, and if an expected
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message isn’t received in time, the waiting
device will re-send its previous message.
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Let me demonstrate. The PC on the right is a
TFTP client, and the server on the left is a TFTP
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server. To download a file from the server,
the client sends a ‘read request’ message.
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The server then replies with a data
message, containing part of the file.
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The client replies with an Ack, but for some
reason the message doesn’t reach the server.
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Because the client sent the Ack, it is waiting for
the next data message, but it doesn’t come. So,
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the client retransmits the Ack message, which
successfully reaches the server. The server then
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replies with the next data message, and the client
replies with an Ack. This exchange will continue
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until the client has received the entire file.
This is called ‘lock-step’ communication.
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The client and server alternately send a message
and then wait for a reply, send a message,
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wait for a reply, etc. The server will never
send two data messages in a row, for example,
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except in the case of retransmission. So, this
method of reliability isn’t as efficient as TCP’s
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forward acknowledgment and sliding
window, but it gets the job done.
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Next, let me introduce TFTP’s connections.
TFTP file transfers have three phases.
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First, the connection phase. The
client sends a request to the server,
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and the server responds back, initializing the
connection. Then the data transfer occurs, and
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data and acknowledgment messages are exchanged.
After the last data message a final Ack message
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is sent, terminating the connection. Let me
demonstrate. So, the client sends a request,
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and the server replies by sending the first data
packet. The connection is officially established.
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The client responds with an Ack, and there is an
exchange of data packets and Acks. These messages,
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including the first data packet, are the data
transfer portion of the file transfer. Finally,
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the client sends an Ack for the last data packet,
and the connection is terminated. So, although
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TFTP doesn’t use TCP, it does have a basic way of
managing connections within the protocol itself.
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Now I’m going to introduce an interesting part
of TFTP’s operation. This isn’t something you
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have to know for the CCNA exam, I just thought it
was interesting so I’m going to share it briefly.
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As expected, when the client sends
the first message to the server,
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the destination port is UDP port 69 and the source
is a random ephemeral port. In TFTP this random
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port is called a ‘Transfer Identifier’, TID, and
is used to identify that particular data transfer.
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However, here’s where the functionality
is different than you might expect.
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The server then also selects a random TID
to use as the source port when it replies.
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It doesn’t use port 69 as the source port.
Then, when the client sends the next message,
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the destination port will be the server’s TID,
again not 69. So, I’ll demonstrate how that works.
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The client sends a message to the server with a
random source port and a destination port of 69.
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When the server replies, instead of using 69 as
the source port it also uses a random port. Then
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the client replies, and uses that random port as
the destination port, it no longer uses port 69.
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And the devices continue to use these two random
ports throughout the data transfer. So, TFTP’s
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well-known port of 69 is only used in the very
first message from the client to the server. As
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I mentioned, this is beyond the scope of the CCNA,
but it’s an interesting part of TFTP’s operation.
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Okay, so that was a brief overview of TFTP
with a few details about its operation.
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Next I’ll introduce FTP and then we’ll compare
the two. FTP was first standardized in 1971.
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This is actually before TCP and
IP, so FTP is a very old protocol,
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although it has of course been updated
since. FTP uses TCP ports 20 and 21,
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instead of just a single well-known port. In
the next slide you’ll see why. Unlike TFTP,
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usernames and passwords are used for
authentication. However, just like in TFTP,
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there is no encryption. Everything is sent in
plain text, including the user name and password.
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For greater security, FTPS, FTP over SSL/TLS,
can be used. This protocol is also called
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FTP Secure. Another option is SSH File Transfer
Protocol, SFTP. Note that FTPS is an upgrade to
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FTP, adding greater security, whereas SFTP is a
different protocol that just has a similar name.
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FTP is more complex than TFTP and
allows not only file transfers,
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but clients can also navigate file directories,
add and remove directories, list files, etc.
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In TFTP, the client could only tell the server
‘give me this file’ or ‘take this file’,
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it couldn’t even ask the server ‘what files do
you have?’. The client sends FTP commands to
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the server to perform FTP’s functions.
There are many different FTP commands,
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and you can view a list of them here
on Wikipedia if you’re interested.
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As I said, FTP uses two different
well-known ports: TCP ports 20 and 21.
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That’s because FTP uses two types of connections.
An FTP control connection to TCP port 21
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is established and used to send FTP commands. The
client sends commands when it wants to perform an
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action, such as retrieving a file from the server,
and the server sends replies to acknowledge.
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However, the actual data transfer isn’t
done using this control connection.
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When files or data are to be transferred,
separate FTP data connections to TCP port 20
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are established and terminated as needed. So, let
me demonstrate the control connection. The client
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initiates the TCP connection, and the usual
SYN, then SYN-ACK, then ACK exchange is used.
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Now the FTP control connection is established.
The client will send FTP commands to the server,
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for example to say that the PC wants to get
a file from the server. The server replies to
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acknowledge the command. But now we need an FTP
data connection to actually transfer the data.
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There are actually two different modes which
can be used to establish an FTP data connection.
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The default method of establishing FTP data
connections is active mode, in which the server
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initiates the TCP connection. So, as you can see
the first arrow, which would be the initial TCP
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SYN message, is from the server to the client.
Now the FTP data connection is established,
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and the data can be exchanged. So, the point I
want you to remember is that in FTP active mode,
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the server initiates the data connection. Also,
note that the FTP control connection is maintained
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throughout this whole process. It isn’t
terminated, so there are two active connections.
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So, active is considered the ‘normal’
mode of initiating FTP data connections.
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However, notice the network has changed. The
client is now behind a firewall. In FTP passive
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mode, the client initiates the data connection.
This is often necessary when the client is behind
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a firewall, which could block the incoming
connection from the server. So, now the first
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message in the TCP connection is initiated by the
client. The firewall permits the server’s replies,
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but it would block the message if the server
tried to initiate the TCP connection itself.
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Once the FTP data connection is established, the
data is exchanged. So, here’s what I want you
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to remember. Firewalls usually don’t permit
‘outside’ devices to initiate connections.
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In this case, FTP passive mode is used and
the client, which is behind the firewall,
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initiates the TCP connection. By the way,
if you’re interested in learning more about
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firewalls, consider studying for the CCNP security
certification at some point in the future.
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Okay, that’s enough about FTP. FTP is more
complex than TFTP and it would take a long
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time to really cover all there is to know
about FTP, but I think that’s enough for
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now. So let’s briefly compare FTP and TFTP. FTP
uses TCP for connection-based communication.
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Port 20 is used for data connections, and
port 21 is used for control connections.
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TFTP on the other hand uses UDP port
69 for connectionless communication,
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although there is a basic form of
connection within the protocol itself.
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FTP clients can use commands to perform various
actions, not just copy files. However TFTP
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clients can only copy files to or from the
server. They can’t delete files, list files, etc.
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FTP uses usernames and passwords to limit who
can access the server. TFTP, on the other hand,
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has no authentication system at all. So, FTP is
a more complex protocol, and TFTP is simpler.
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Okay, let’s move on to look at the IOS file
systems. This is going to be a very brief
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introduction, just this slide, but I want
to introduce it because we will be looking
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at transferring files from TFTP and FTP servers
onto a Cisco IOS device. A file system is a way
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of controlling how data is stored and retrieved.
If you have a PC, it certainly has its own file
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system. You can view the file systems of a Cisco
IOS device with the command SHOW FILE SYSTEMS.
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And here’s some sample output. Note that there
are quite a few file systems, and I even cut out
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a few because the output was too long. And note
that there are different types of file systems.
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The disk type refers to storage devices such as
flash memory. This is usually where the Cisco
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IOS file itself is stored. When the device boots
up, it copies the IOS file from flash into RAM.
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The opaque disk type is used for specific internal
functions. These refer to logical internal
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systems, not actual separate storage devices. The
NVRAM type refers to the NVRAM, non-volatile RAM,
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of the device. Normal RAM loses all of
its data when the device loses power.
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However NVRAM does not. The startup-config file is
stored in NVRAM. There is also the network type.
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This represents external file systems, for
example FTP or TFTP servers. I don’t think
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you’ll find any questions about these file
systems on the exam, the topic was removed
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in the newest version of the CCNA. So, we’ll
end this introduction here. Next let’s actually
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look at how to use TFTP and FTP to transfer
files into the flash memory of Cisco devices.
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So, here’s a very simple network we’ll use
to demonstrate TFTP and FTP. R1 is a Cisco
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router running Cisco IOS, and we have downloaded
a new version of IOS and saved it on SRV1. SRV1
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is a server running both TFTP and FTP, and
we’ll try out both of them to get the new
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version of IOS from SRV1 onto R1. First, you can
view the current version of IOS running on R1 with
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SHOW VERSION. Here you can see the image name,
C2900-UNIVERSALK9-M. Notice the K9, meaning it
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supports cryptographic features like SSH. Then
the version number, 15.1(4)M4. Perhaps in a future
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video I’ll talk about the naming conventions of
IOS versions, but I’ll skip over it for now. The
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output of SHOW VERSION is actually quite
long, I’m just showing the top portion.
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By the way, for simplicity’s sake I’m actually
using packet tracer for this demonstration,
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although usually I use GNS3. You can also
view the contents of flash with SHOW FLASH.
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Here it is, and you can see the IOS image
here. So, what we’re going to do now is use
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TFTP to copy a new version of IOS from SRV1
to the flash of R1, configure R1 to boot
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with the new version of IOS, and then
finally delete the old version from flash.
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And here’s how to copy the file using TFTP. The
command is COPY, followed by the source and the
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destination. By using TFTP as the source,
you tell the router that you want to access
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a TFTP server. The router then asks you
for the IP address of the remote host.
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This is where you enter the TFTP server’s IP
address. Then enter the source filename, the name
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of the file you want to download. Note that you
have to know this beforehand. TFTP isn’t capable
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of asking a server ‘what files do you have?’. I
already knew the name of the file on the server,
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so I entered it. Then you’re asked what name
you want to save the file as on the router.
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You can just hit enter to accept the default name,
which is the same name as on the TFTP server.
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And that’s it, the file is then transferred
from the TFTP server to the router.
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I used SHOW FLASH to check the contents of flash.
Here you can see the new version of IOS that was
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copied from the TFTP server. Now, how do we make
the router use this file as its OS instead of
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the old file? From global config mode, use the
command BOOT SYSTEM, followed by the filepath.
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Note that, if you don’t use this command
the router will boot using the first IOS
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file it finds in flash. So, you should use this
command to force it to use the newer version.
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After that, make sure you save the configuration
before reloading the device, or the BOOT SYSTEM
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command won’t take effect. Then simply use
the RELOAD command to restart the device.
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After the device finished restarting I used SHOW
VERSION to check the running version of IOS,
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and R1 is now using the new version, 15.5,
instead of the old one, 15.1. Finally, let’s
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delete that old version of IOS. We don’t need it
anymore, it’s just taking up space on the device.
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The command to delete a file is
DELETE, followed by the filepath.
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It asks you to confirm, so I did. And then I
used SHOW FLASH to view the contents of flash,
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and now the old file is gone.
So, we successfully used TFTP
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to copy an IOS file to R1 from a TFTP server. We
then configured R1 to boot using that IOS file,
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and then reloaded R1. Finally, we deleted
the old IOS image from the device.
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Now let’s take a look at FTP. I’ll only show
the process of transferring the file from the
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server to the router, because the rest is
the same. Once the file is on the device,
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the other steps such as the BOOT SYSTEM command,
deleting the old file, etc, are all the same.
00:22:00
First, you should configure the username
and password that the router will use when
00:22:03
connecting to an FTP server. Remember, FTP
authenticates using a username and password.
00:22:10
So, this same username and password
must be configured on the server, too.
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In this case, I configured the username and
password as cisco. Then the copy command itself
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is basically the same. COPY FTP: FLASH:, and then
enter the FTP server’s IP address, the source file
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name, and the name you want to save the file
as on the local router. That’s it. Then to
00:22:36
upgrade the IOS we could use the same BOOT SYSTEM
command, save the config, and reload the router.
00:22:44
Okay, here are the commands we just used.
If you don’t remember any of these commands,
00:22:49
go back in the video to review. I
also want to say something about the
00:22:54
COPY command. This actually isn’t the first time
we’ve seen that command. Previously I introduced
00:23:00
it as COPY RUNNING-CONFIG STARTUP-CONFIG, as a
method to save the configuration of the device.
00:23:07
It copies the source, the current running
config, to the destination, the startup config.
00:23:15
Okay, before the quiz let’s review what we
covered. First, the purpose of FTP and TFTP.
00:23:22
Basically, they allow you to
transfer files between devices
00:23:26
over a network. Then I gave an overview of TFTP
and FTP, and compared the two. TFTP is simpler
00:23:35
and useful for quickly transferring
small files in a controlled environment,
00:23:39
but has no advanced functionalities
or any security features.
00:23:44
FTP has much greater functionality, and includes
username and password authentication. And if you
00:23:50
use FTPS, it has many other security benefits,
but that’s out of the scope of this video.
00:23:58
Then I very briefly introduced the file systems in
Cisco IOS. And finally showed how to use TFTP and
00:24:05
FTP to get a new IOS file from a server, and then
reboot the device with the new version of IOS.
00:24:13
Once again, make sure to watch until the end
of the quiz for a bonus question from Boson
00:24:17
Software’s ExSim, the best practice exams for the
CCNA. Okay, let’s go to question 1 of the quiz.
00:24:27
Which of the following
statements about FTP are true?
00:24:30
Select two. Pause the video
now to think about the answers.
00:24:38
The answers are B, FTP control
connections use TCP port 21,
00:24:42
and D, FTP data connections use TCP port 20.
00:24:47
FTP uses TCP to provide reliable communications
and other features. It uses port 21 to establish a
00:24:55
control connection for sending FTP commands and
replies to those commands, and then uses port
00:25:01
20 to establish data connections for the actual
exchange of data. Okay, let’s go to question 2.
00:25:09
Which of the following commands can be used to
transfer a file from an external TFTP server
00:25:14
to the local device’s flash storage? Pause
the video now to think about the answer.
00:25:23
The answer is A, COPY TFTP: FLASH:. The command
is COPY, then the source and then the destination,
00:25:31
so this copies a file from a TFTP server
to flash. Okay, let’s go to question 3.
00:25:40
R1 is behind a firewall and wants to
connect to an external FTP server.
00:25:45
Which of the following statements is true?
Pause the video now to think about the answer.
00:25:55
The answer is C, R1 should use FTP
passive mode for the data connection.
00:26:01
Active and passive mode only
apply to the FTP data connections,
00:26:05
because the client always initiates the control
connection. In active mode, the server initiates
00:26:11
the data connection. But in passive mode,
the client initiates the data connection.
00:26:16
When a client is behind a firewall, passive mode
should be used. Okay, let’s go to question 4.
00:26:24
Which type of file system is used to store the
startup-config of a device running Cisco IOS?
00:26:30
Pause the video now to think about the answer.
00:26:36
The answer is D, NVRAM. NVRAM, non-volatile
RAM, is a type of RAM that preserves data
00:26:44
even after the device loses power. It
is used to store the startup-config
00:26:49
of the device. Okay, let’s go to question 5.
00:26:55
Which of the following functions
are NOT possible when using TFTP?
00:26:59
(select two). Pause the video
now to think about the answers.
00:27:08
The answers are B, create a new directory on a
server, and C, list the contents of a server.
00:27:16
TFTP is very simple and only
allows a client to copy a file
00:27:20
to or from a server, it has no other functions.
Okay, that’s all for the quiz. Now let’s take
00:27:26
a look at a bonus question from
Boson Software’s ExSim for CCNA.
00:27:33
Okay here's today's Boson ExSim practice
question. Which of the following Application
00:27:38
layer protocols use UDP for unsynchronized,
connectionless data transfer? Select 2 choices.
00:27:45
So, here are the choices. Pause the
video now to think about the answers.
00:27:54
Okay let's check. So, I think the correct answers
are TFTP. That uses UDP for unsynchronized,
00:28:01
connectionless data transfer. Now, it says
connectionless, but as I showed TFTP does use
00:28:07
some basic kind of connection
within the protocol itself.
00:28:11
But it doesn't use TCP connections at Layer 4, so
it is one of the correct answers. And also SNMP,
00:28:19
Simple Network Management Protocol. As we covered
recently in the course, it also uses UDP. It is
00:28:24
not TCP-based, it doesn't use TCP connections.
And HTTP, I mentioned, does use TCP, and also SMTP
00:28:33
which we don't cover in the course, but that is
Simple Mail Transfer Protocol. It also uses TCP.
00:28:40
Okay, so I will click on show answer. And that
is correct. So, here is Boson's explanation,
00:28:47
which just outlines the different protocols and
explains about TCP and UDP. So, you can pause the
00:28:53
video now to read Boson's explanation. Okay, so
that was a quick look at a bonus question in Boson
00:29:03
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00:29:09
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00:29:17
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00:29:20
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00:29:24
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00:29:29
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00:29:41
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00:29:46
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