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What is VLAN TCI?
VLAN Tagging allows an individual IP Address to be configured as part of multiple VLANs. When configured, each outgoing packet is tagged with a VLAN ID tag compliant to IEEE 802.1Q VLAN specifications. The VLAN Aware Ethernet Switch or router extracts the tag and routes the packet into the correct VLAN Group.
What is tag control information TCI?
Tag control information (TCI) A 16-bit field containing the following sub-fields: Priority code point (PCP) A 3-bit field which refers to the IEEE 802.1p class of service and maps to the frame priority level. Different PCP values can be used to prioritize different classes of traffic.
What the VLAN tag control information field consists of?
The VLAN tag is a two-byte field inserted between the source MAC address and the Ethertype (or length) field in an Ethernet frame. Another two-byte field, the Tag Protocol Identifier (TPI or TPID), precedes the VLAN tag field.
Which VLAN is used for untagged information?
native VLAN
Recall that the native VLAN is the VLAN associated with untagged traffic. Mismatched native VLAN’s on opposite sides of a trunk can inadvertently create “VLAN hopping”. This is often a method of intentional attack used to sneak into a network and is an open security risk.
What is a VLAN tag?
A VLAN tag is a unique identifier that indicates the VLAN to which a frame belongs. On receiving a tagged frame, the switch inspects the frame header and, based on the VLAN tag, identifies the VLAN. The switch then forwards the frame to the destination in the identified VLAN.
What is the tag control information ( TCI ) field?
Tag control information (TCI) A 16-bit field containing the following sub-fields: Priority code point (PCP) A 3-bit field which refers to the IEEE 802.1p class of service and maps to the frame priority level. Different PCP values can be used to prioritize different classes of traffic. Drop eligible indicator (DEI)
How is a VLAN tag defined in IEEE 802.1Q?
Tagging 802.1Q VLAN frames are distinguished from ordinary Ethernet frames by the insertion of a 4-byte VLAN tag into the Ethernet header. It is placed between the source MAC and the EtherType fields: The first two bytes of the tag contain the TPID (tag protocol identifier), which is defined to be equal to 0x8100.
How big is the frame size of a VLAN tag?
Except for frames in the native VLAN, when a switch puts a frame on a trunk, it inserts a VLAN tag into the frame. The TCI is 16 bits, which increases the maximum frame size from 1518 bytes to 1522 bytes. The first four bits basically serve the purpose of layer-2 QoS.
How many bits are in a VLAN identifier?
The remaining two bytes contain the TCI (tag control information), of which 12 bits correspond to the VID (VLAN identifier, described below) and 4 bits contain metadata used for quality of service management.