NFS Services Administrator's Guide

Configuring and Administering NFS
Configuring and Administering AutoFS
Chapter 2112
The /etc/netmasks file contains Internet Protocol (IP) address
masks with IP network numbers. It supports both standard
subnetting as specified in RFC-950 and variable length subnetting as
specified in RFC-1519. When using the standard subnetting, there
should be a single line for each network with the network number
and the network mask to use on that network. The network number
and mask can be specified in the conventional IP ‘.’(dot) notation. The
network number is restricted to be a class A, B or C network number.
For example:
# network number netmask
128.32.0.0 255.255.255.0
When using variable length subnetting, the format is identical.
However, there should be a line for each subnet with the first field
being the subnet and the second field being the netmask.
The following example shows how AutoFS uses /etc/netmasks file
to determine the local client’s subnets in the replicated servers
environment. In this example, servers sage and thyme export
/nfs/mont, the IP address for server sage is 15.43.232.30 and the
IP address for server thyme is 15.244.10.20:
# /etc/auto_direct file
/nfs_mount sage,thyme:/user
#/etc/netmasks file on the client basil:
#network number netmask
15.43.234.210 255.255.248.0
AutoFS uses /etc/netmasks file to determine the local client’s
subnets and mounts /nfs/mount from the server sage on the local
subnet.
Directories with multiple servers should be mounted read-only to ensure
that the versions remain the same on all the servers.
When a user requests access to a directory with multiple servers
configured, AutoFS polls all the servers simultaneously and mounts the
directory from the server that responds first. Multiple servers give users
reliable access to a mounted directory, because if one server is down, the
directory can be mounted from another. Also, multiple servers provide
some load balancing across the network; a server that is not busy will
respond more quickly to AutoFS’s poll than one that is heavily loaded, so
the directory will be mounted from the server that is not busy.