VLAN

The farm has more servers and workstations than there are ethernet jacks on the walls of the room. Therefore, two virtual LANs are set up so that all machines can make use of both the farm and UNH networks (more). Ports 1 through 22 on the switch default to the farm network. Therefore, the majority of machines that are connected to the switch through device "eth0" will have access only to each other unless 1) they have an additional, physical connection to a wall jack, or 2) they are configured to use VLAN id 2, a.k.a. "eth0.2".

Here is an article on VLAN under Linux: Linux Journal

Software

/sbin/vconfig

Used to create virtual network devices, among other things. Creation is all we currently use it for.

/sbin/ifdown, /sbin/ifup

Used for shutting down and starting network interfaces. "Unfortunately, they, like far too many tools, assume a set naming scheme for ethernet family devices. (I might file a bug report if I get around to it:Aaron)." However, with aliases, devices can be referred to as "farm" and "unh" rather than "eth0" and "eth0.2".

/usr/bin/system-config-network

Fedora/Redhat GUI tool for configuring network devices, etc. Much nicer than editing config files by hand, setting aliases is easy, and has ifup, ifdown functionality

Configuration Files

From /usr/share/doc/initscripts-8.11.1/sysconfig.txt:

 /etc/sysconfig/network-scripts/ifcfg-<interface-name> and
 /etc/sysconfig/network-scripts/ifcfg-<interface-name>:<alias-name>:
   The first defines an interface, and the second contains
   only the parts of the definition that are different in a
   "alias" (or alternative) interface.  For example, the
   network numbers might be different, but everything else
   might be the same, so only the network numbers would be
   in the alias file, but all the device information would
   be in the base ifcfg file.

In-depth details here: Ifcfg_files_details, but the key is to make sure that eth0.2's configuration has VLAN=yes in it.

Additional Information

• General Network Configuration Notes