Building Internet Firewalls, 2nd Edition

Chapter 17. File Transfer, File Sharing, and Printing

Although files can be sent from one computer to another via electronic mail, email tends to be an inefficient way of transferring data, best suited for relatively small documents. Other protocols are better for moving large files around. These protocols come in two kinds: protocols designed for file transfer, and protocols designed for file sharing. In file transfer, a user copies a file to or from a server, so that one file is on the server and another copy of the file is on the client. In file sharing, the file remains on the server and is modified by the client, so that only one copy of the file exists. The file sharing model is particularly useful in situations where multiple people need to work on a file.

When using mobile computers, it is useful to have some sort of hybrid between these two options; a mobile computer may not be able to contact a file server to use a file that’s located on the server, so local copies are desirable, but the mobile is unlikely to be reliably backed up and accessible to other people, so server-based files are desirable. Although there are various solutions to this situation, all of them involve using existing protocols designed for file transfer or for file sharing. The most common versions are programs like Microsoft’s Briefcase, which use file sharing to synchronize files between a mobile computer and a server.

FTP is the de facto standard for file transfer on the Internet. In addition, some ...