Vlan Membership - KTI Networks KGS-1064-HP User Manual

as an IEEE 802.1Q-tagged frame. This field is located at the same position as the EtherType/length field in
untagged frames, and is thus used to distinguish the frame from untagged frames.
Tag control information (TCI): divided into PCP, DEI, and VID
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.
Drop eligible indicator (DEI): a 1-bit field. (formerly CFI). It may be used separately or in conjunction with
PCP to indicate frames eligible to be dropped in the presence of congestion.
VLAN identifier (VID): a 12-bit field specifying the VLAN to which the frame belongs.
Untagged frame: A standard Ethernet frame with no VLAN Tag field
Priority-tagged frame: An IEEE 802.1Q frame which VID field value is zero (VID=0)
VLAN-Tagged frame: An IEEE 802.1Q frame which VID field value is not zero (VID>0)
Double tagging, Double Tags: With the IEEE standard 802.1ad, double-tagging can be useful for Internet
service providers, allowing them to use VLANs internally while mixing traffic from clients that are already
VLAN-tagged. The outer (next to source MAC and representing ISP VLAN) S-TAG (service tag) comes first,
followed by the inner C-TAG (customer tag). In such cases, 802.1ad specifies a TPID of 0x88a8 for
service-provider outer S-TAG.
C-tag: Tag with TPID 0x8100
S-tag: Tag with TPID 0x88A8
Priority S-tagged frame: Priority tagged frame with S-tag (TPID=0x88A8, VID=0)
Priority C-tagged frame: Priority tagged frame with C-tag (TPID=0x8100, VID=0)
>
VLAN S-tagged frame: Tagged frame with S-tag (TPID=0x88A8, VID 0)
>
VLAN C-tagged frame: Tagged frame with C-tag (TPID=0x8100, VID 0)
PVID (Port VID): PVID is the default VID of an ingress port. It is used in 802.1Q filtering for untagged
packets. It is also often used as [Default Tag - VID] for egress tagging operation.

2.14.2 VLAN Membership

-115-