FTP & TFTP

Done

FTP (File Transfer Protocol) and TFTP (Trivial File Transfer Protocol) are both industry standard protocols. They are used to transfer files over the network, however there are some differences between each one.

In Network Administration, one of the roles of this protocols, is to upgrade the image file of the IOS. You will usually have an FTP/TFTP server to copy from or to.

TFTP

The “Trivial” keyword stands for simplicity. TFTP is a lightweight version of FTP, has only ONE capability: copy file from or to a TFTP server, that`s it.

Also, it does that WITHOUT any Encryption or Authentication. So it is better fitted for a controlled environment.

It uses the UDP Port 69 to reach the server TFTP service. HOWEVER, despite the UDP protocol it DOES HAVE RELIABILITY FEATURES. It uses the “lock-step” mechanism of using timers and acknowledgments to assure the data is delivered, it does that with the messages:

Read Request

Data

Connections types

Connection: It is initiated with a “Read Request” from the client to the server, then the server establishes the connection by sending a data message or refuse it with an error message.

Data Transfer: It is the actual transfer of data with Data and Ack messages that assure reliability to the process.

Connection Termination: After the last Data message has been sent, the client will reply with the last Ack message, terminating the connection.

Interesting Fact

TFTP only uses the UDP Port 69 to initiate the connection, after that the Server will use a random port (TFTP Transfer Identifier (TID)) as the source and the client will start to use that port as the destination.

FTP

It is a more complete solution than TFTP. It was created before TFTP however.

It has Authentication, but no Encryption. For encryption there is the upgraded version of FTP, called FTPS (FTP over SSL/TLS) or the new protocol SFTP (SSH File Transfer Protocol).

It can do the following:

Add/Remove Directories

List the files

Browse directories

Copy files from and to a server

etc.

Another great difference is the fact that FTP establishes two simultaneous connections while being used:

Control: It the first established connection with the port TCP 21 and is used only to send and receive commands.

Data: It is the actual data exchange, created as a consequence of a command, through the port TCP 20. It can be initiated by two methods:
- Active mode: It is the normal situation, where the TCP handshake to establish the Data connection is made by the server. In other words, it is the server that will send the first TCP SYN message.
- Passive mode: This is the reverse, the client sends the first SYN Message. This is usually used for situations where the client sits behind a firewall, where connections can`t be started by the outside.

FTP vs TFTP

FTP	TFTP
TCP 20 (data) and TCP 21 (control	UDP 69
Multiple features (delete files, list files, browse directories, create and delete directories, copy files, etc.)	Only Copy files to or from a server
Authentication	NO Authentication
Complex	Simple

File Systems

A file system is responsible for knowing where the data is stored and how to retrieve it. There are multiple file systems in Cisco IOS.

There are the following types of file systems:

disk: Actual storage devices, like flash memory. It is where the IOS is stored, after boot it will be loaded into the RAM.

opaque: Logical file systems used for internal functions

nvram: Non-volation RAM responsible for storing the startup-config

network: External file systems, like FTP/TFTP servers.

Show commands

List File Systems

show file systems

See the current version of IOS

show version

See the files in the flash memory

It can show the image of the IOS.

show flash

Upgrade Cisco IOS from a TFTP/FTP Server

Copy the file into flash

//Option#1 - TFTP
copy tftp: flash:  //Yes, it is done in Privileged EXEC mode
//Fill the fields that will be prompted

//Option#2 - FTP
configure terminal
ip ftp username {username}
ip ftp password {password}
exit
copy ftp: flash:   //Privileged Exec Mode

Check if the file was indeed downloaded
```
show flash
```

Select the file and boot from it

configure terminal
boot system flash:{file-name}
exit
write memory
reload

Ensure that the correct file was booted
```
show version
```

Erase the old version IOS file

show flash
delete flash:{old-file-name}
show flash

Resume of commands