Editing VLAN (section)

==Protocols and design==
The protocol most commonly used today to support VLANs is [[IEEE 802.1Q]].  The [[IEEE 802.1]] working group defined this method of multiplexing VLANs in an effort to provide multivendor VLAN support.  Prior to the introduction of the 802.1Q standard, several [[proprietary protocol]]s existed, such as [[Cisco Inter-Switch Link]] (ISL) and [[3Com]]'s Virtual LAN Trunk (VLT).  Cisco also implemented VLANs over [[FDDI]] by carrying VLAN information in an [[IEEE 802.10]] frame header, contrary to the purpose of the IEEE 802.10 standard.

Both ISL and IEEE 802.1Q perform ''explicit tagging'' – the frame itself is tagged with VLAN identifiers. ISL uses an external tagging process that does not modify the Ethernet frame, while 802.1Q uses a frame-internal field for tagging, and therefore does modify the basic Ethernet frame structure.  This internal tagging allows IEEE 802.1Q to work on both access and trunk links using standard Ethernet hardware.

===IEEE 802.1Q===
{{Main|IEEE 802.1Q}}
Under IEEE 802.1Q, the maximum number of VLANs on a given Ethernet network is 4,094 (4,096 values provided by the 12-bit {{abbr|VID|VLAN identifier}} field minus reserved values at each end of the range, 0 and 4,095).  This does not impose the same limit on the number of IP subnets in such a network since a single VLAN can contain multiple IP subnets. [[IEEE 802.1ad]] extends the number of VLANs supported by adding support for multiple, nested VLAN tags. [[IEEE 802.1aq]] (Shortest Path Bridging) expands the VLAN limit to 16 million. Both improvements have been incorporated into the IEEE 802.1Q standard.

===Cisco Inter-Switch Link===
{{Main|Cisco Inter-Switch Link}}
Inter-Switch Link (ISL) is a Cisco proprietary protocol used to interconnect switches and maintain VLAN information as traffic travels between switches on trunk links. ISL is provided as an alternative to IEEE 802.1Q. ISL is available only on some Cisco equipment and has been deprecated.<ref>CCNA Exploration LAN Switching and Wireless course, v 4.0, sec 3.2.3</ref>

===Cisco VLAN Trunking Protocol===
{{Main|VLAN Trunking Protocol}}
VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol that propagates the definition of VLANs on the whole local area network. VTP is available on most of the [[Cisco Catalyst]] Family products. The comparable IEEE standard in use by other manufacturers is [[GARP VLAN Registration Protocol]] (GVRP) or the more recent [[Multiple VLAN Registration Protocol]] (MVRP).

=== Multiple VLAN Registration Protocol ===
{{main|Multiple Registration Protocol}}
Multiple VLAN Registration Protocol is an application of Multiple Registration Protocol that allows automatic configuration of VLAN information on network switches. Specifically, it provides a method to dynamically share VLAN information and configure the needed VLANs.