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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.
VLANs are data link layer (OSI layer 2) constructs, analogous to Internet Protocol (IP) subnets, which are network layer (OSI layer 3) constructs. In an environment employing VLANs, a one-to-one relationship often exists between VLANs and IP subnets, although it is possible to have multiple subnets on one VLAN.
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.
The QoS technique developed by the working group, also known as class of service (CoS), is a 3-bit field called the Priority Code Point (PCP) within an Ethernet frame header when using VLAN tagged frames as defined by IEEE 802.1Q. It specifies a priority value of between 0 and 7 inclusive that can be used by QoS disciplines to differentiate ...
Conversely, an administrator can combine systems on separate local area networks (LANs) into a single VLAN spanning segments of a large network. External network virtualization is envisioned to be placed in the middle of the network stack and help integrating different architectures proposed for next generation networks.
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 ...
It is a method of inter-VLAN routing where one router is connected to a switch via a single cable. The router has physical connections to the broadcast domains where one or more VLANs require the need for routing between them. Devices on separate VLANs or in a typical local area network are unable to
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 ...