TCP/IP Tutorial and Technical Overview - IBM Redbooks

► The NFS protocol performs the file I/O to the remote file system.
Both the Mount and NFS protocols are RPC applications that implement the
client/server model (see Figure 11-1 on page 409) and are transported by both
TCP and UDP.
Mount protocol
The Mount protocol is an RPC application shipped with NFS and uses program
number 100005. The MOUNT command acts as an RPC server program and
provides a total of six procedures when accessing remote systems:
NULL Does nothing. Useful for server response testing.
MNT MOUNT function. Returns a file handle pointing to the directory.
DUMP Returns the list of all mounted file systems.
UMNT Removes a mount list entry.
UMNTALL Removes all mount list entries for this client.
EXPORT Returns information about the available file systems.
A file handle is a variable-length array with a maximum length of 64 bytes and is
used by clients to access remote files. They are a fundamental part of NFS,
because each directory and file are referenced only through file handles. For this
reason, some implementations increase the security of the protocol by
encrypting the handles. The file handles are obtained by executing the MOUNT
application’s MNT procedure, which locates the remote file system within the file
hierarchy, and returns the file handle. Following the MOUNT command, a user
can access the remote file system as though it were a part of the local file
system.
For example, consider two remote hosts:
► HostA implements a hierarchical file system consisting of numerous
directories and subdirectories.
► HostB does not implement a hierarchical file system, but instead implements
a series of minidisks, with each minidisk appearing as a separate folder.
A user on HostA issues the MOUNT command to locally mount a minidisk from
HostB. However, the user does not see the mounted volume as a minidisk, but
instead sees it in the context of the hierarchical file system of HostA.
Although specific implementations can provide additional features, the generic
syntax of the MOUNT command is as follows:
MOUNT -o options host:rvolume lvolume
Chapter 14. File-related protocols 539