TCP/IP and the DoD Model
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Network File System (NFS)
Network File System (NFS)
is a jewel of a protocol specializing in file
sharing. It allows two different types of file systems to interoperate.
It works like this: Suppose the NFS server software is running on an
NT server, and the NFS client software is running on a Unix host. NFS
allows for a portion of the RAM on the NT server to transparently store
Unix files, which can, in turn, be used by Unix users. Even though the NT
file system and Unix file system are unlike--they have different case sen-
sitivity, filename lengths, security, and so on--both Unix users and NT
users can access that same file with their normal file systems, in their
normal way.
Simple Mail Transfer Protocol (SMTP)
Simple Mail Transfer Protocol (SMTP)
, answering our ubiquitous call to
e-mail, uses a spooled, or queued, method of mail delivery. Once a message
has been sent to a destination, the message is spooled to a device--usually
a disk. The server software at the destination posts a vigil, regularly check-
ing this queue for messages. When it detects them, it proceeds to deliver
them to their destination. SMTP is used to send mail; POP3 is used to
receive mail.
Line Printer Daemon (LPD)
The Line Printer Daemon (LPD) protocol is designed for printer sharing. The
LPD, along with the LPR (Line Printer) program, allows print jobs to be
spooled and sent to the network's printers using TCP/IP.
TFTP is completely different than FTP, not just because it is connectionless
but also because you cannot just put a TFTP server on the Internet and list
files for people to share. When you install a TFTP client, you choose the
default directory. When you use TFTP, the file is either taken from this direc-
tory and put somewhere else or downloaded into this directory. You cannot
list files with TFTP nor tell TFTP where to put the file. Later in this book,
you'll use TFTP to both back up and download a new Internetwork Operat-
ing System (IOS) to and from your Cisco router.
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