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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.
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.
As VLANs are segmented, it reduces the amount of traffic flow through a connection. By separating VLANs, it provides enhanced network security. Network administrators have direct control over multiple broadcast domains. In the event of a malicious user attempting to access any switch port, they will have limited access to the network.
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.
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.
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.
One VLAN mapped to multiple spanning trees is not allowed. All the VLANs are mapped to the CIST by default. Once a VLAN is mapped to a specified MSTI, it is removed from the CIST.To avoid unnecessary STP processing, a port that is attached to a LAN with no other bridges/switches attached, can be configured as an edge port.
CSTs are backward compatible with the STP and RSTP standard. A MST that has only one VLAN assigned to it is an internal spanning tree (IST). [20] Unlike some proprietary per-VLAN spanning tree implementations, [28] MSTP includes all of its spanning tree information in a single BPDU format. Not only does this reduce the number of BPDUs required ...