The Rock says this: The Rock says, this is a nodeshell rescue. The Rock is going to take this nodeshell, shine it up, turn it sideways, and shove it straight into ENN.
VLANs, or, Save Big On Cables!
A Virtual Local Area Network is a logical grouping of end stations that subnets a physical LAN into broadcast domains. Any LAN segment can be combined into a group that appears as a single LAN. VLANs can be trunked over mixed networks, like ATM, FDDI, and Fast Ethernet. As far as I know, there are three protocols available for VLAN routing: Inter-Switch Link (ISL), IEEE 802.10, and
ATM LAN Emulation (LANE).
Advantages of VLANs
Managability: VLANs can be organized by department, project teams, location, function, protocol, application, or subnet address - again, regardless of physical location, though geographic VLANs are the most popular, given the recent move to centralized server farms and such.
Adminstrators have control over each port, and what resources that port is allowed is use. They can put restrictions on protocol, applications, and hardware addresses, etc.
Security: VLANs allow those with certain permissions (higher security) to be grouped together in their own VLANs. It restricts all users outside the same VLAN (um, hopefully).
Bandwidth: Packets are switched only between ports on the VLAN. Traffic coming from one LAN is contained to other LANs in the same VLAN, as opposed to traditional LANs where traffic is usually forwarded without need. All broadcast and multicast traffic is contained within the VLAN.
You can update switch databases with VTP, or Virtual Trunk Protocol, which is used to send VLAN info across a trunked link to switches in a domain.
note: I'm Cisco-biased.