Question

Critique how FTP solves the problem of file transfer – what is good? What is bad? What is weird?

Answer 1

FTP: FILE TRANSFER PROTOCOL

It is a protocol that is used for transforming a file from one location to another i.e from one host to another host. It is a standard mechanism that is provided by TCP/IP. Transforming files from one system to another seems very simple, but there are some problems that need to deal first before transforming files.

For example, two systems may use a different file name convention, two systems may have different directory structures, Two systems may have a different way of representing data, This all problems are resolved by File Transfer Protocol. Before Transforming files from one host to another it takes care of this thing and then transfers the files.

It uses TCP services. It needs two TCP connections. One is Control connection and another is Data connection. For control connection, it uses well-known port 21 and for data connection, it uses well-known port 20.

Control Connection uses port number 21

There are two steps to establish a control connection –

• Server issues a passive open on the well-known port 21 and waits for the client
• After severing issues passive open, the client issue active open using an ephemeral port.

Data Connection uses port number 20.

At the server site, the data connection uses well-known port 20. There are three steps to establish a data connection –

• Using ephemeral port client issues a passive open. This step must be done by the client not the server because the client wants to transform the file.
• Using the PORT command client sends this port number to the server.
• When the server receives this port number from the client, it issues active open using well-known port 20.

FTP is not recommended for file transfer because it lacks security,encryption is not given, vulnerable attacks are possible,Not All Vendors Are Created Equal,Compliance is an Issue,It’s Difficult to Monitor Activity.