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IEEE 802.1Q, often referred to as Dot1q, is the networking standard that supports virtual local area networking (VLANs) on an IEEE 802.3 Ethernet network. The standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by bridges and switches in handling such frames.
Without VLAN capability, users are assigned to networks based on geography and are limited by physical topologies and distances. VLANs can logically group networks to decouple the users' network location from their physical location. By using VLANs, one can control traffic patterns and react quickly to employee or equipment relocations.
VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol that propagates the definition of Virtual Local Area Networks on the whole local area network. [1] To do this, VTP carries VLAN information to all the switches in a VTP domain. VTP advertisements can be sent over 802.1Q, and ISL trunks.
The alternative is to have different logical switches, but then one of the used links will have to be blocked to ensure a loop-free topology (which can partially be overcome by using Multiple Spanning Tree or Cisco's proprietary per VLAN spanning tree. Spanning Tree Protocol is relatively slow in convergence, which can result in periods that ...
The technique specified by the standard is known informally as stacked VLANs or QinQ. The original 802.1Q specification allows a single virtual local area network (VLAN) header to be inserted into an Ethernet frame. QinQ allows multiple VLAN tags to be inserted into a single frame, an essential capability for implementing metro Ethernet.
A Private VLAN divides a VLAN (Primary) into sub-VLANs (Secondary) while keeping existing IP subnet and layer 3 configuration. A regular VLAN is a single broadcast domain, while private VLAN partitions one broadcast domain into multiple smaller broadcast subdomains. Primary VLAN: Simply the original VLAN. This type of VLAN is used to forward ...
This is known as inter-VLAN routing. On layer-3 switches it is accomplished by the creation of layer-3 interfaces (SVIs). Inter VLAN routing, in other words routing between VLANs, can be achieved using SVIs. [1] SVI or VLAN interface, is a virtual routed interface that connects a VLAN on the device to the Layer 3 router engine on the same device.
Cisco Inter-Switch Link (ISL) is a Cisco proprietary link layer protocol that maintains VLAN information in Ethernet frames as traffic flows between switches and routers, or switches and switches. [1] ISL is Cisco's VLAN encapsulation protocol and is supported only on some Cisco equipment over the Fast and Gigabit Ethernet links.