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3. Advanced Functions
To help a better understanding about the software management interfaces, this chapter describes some
advanced functions provided by the switch.
3.1 Abbreviation
Ingress Port : Ingress port is the input port on which a packet is received.
Egress Port : Egress port is the output port from which a packet is sent out.
IEEE 802.1Q Packets : A packet which is embedded with a VLAN Tag field
VLAN Tag : In IEEE 802.1Q packet format, 4-byte tag field is inserted in the original Ethernet frame
between the Source Address and Type/Length fields. The tag is composed of :
#of bits 16 3 1 12
Frame field TPID User priority CFI VID
TPID : 16-bit field is set to 0x8100 to identify a frame as an IEEE 802.1Q tagged packet
User Priority : 3-bit field refer to the 802.1p priority
CFI : The Canonical Format Indicator for the MAC address is a 1 bit field.
VID : VLAN identifier, 12-bit field identifies the VLAN to which the frame belongs to.
Untagged packet : A standard Ethernet frame with no VLAN Tag field
Priority-tagged packet : An IEEE 802.1Q packet which VID filed value is zero (VID=0)
VLAN-Tagged packet : An IEEE 802.1Q packet which VID filed value is not zero (VID<>0)
PVID (Port VID)
PVID is the default VID of an ingress port. It is often used in VLAN classification for untagged
packets. It is also often used for egress tagging operation.
DSCP : Differentiated Service Code Point, 6-bit value field in an IP packet
VLAN Table lookup : The process of searching VLAN table to find a VLAN which matches the
given VID index
MAC address table lookup : The process of searching MAC address table to find a MAC entry
which matches the given destination MAC address and the port where the MAC address is located
Packet forwarding : also known as packet switching in a network switch based on MAC address
table and VLAN table information
VLAN forwarding : the operation that a packet is forwarded to an egress destination port based on
VLAN table information
VLAN group : configuration information about a VLAN which can be recognized in the switch. The
information includes a VID associated to the VLAN, member ports, and some special settings.