Luxul XMS-1024P - Manual (Page 66)

66
XMS-1024P
a: 14203 Minuteman Drive, Suite 201, Draper, UT 84020-1685 | luxul.com | 801-822-5450
LUX-UG-XMS-1024P Vers: 081314
The Switch can analyze the received untagged packets on the Port and match the
packets with the MAC VLAN, Protocol VLAN and/or 802.1Q VLAN in turn. If a packet
is matched, the Switch will add a corresponding VLAN tag to it and forward it in the
corresponding VLAN.
6.1 802.1Q VLAN
VLAN tags used in the packets are necessary for the Switch to identify packets of
different VLANs. The Switch works at Layer 2 or the Data Link Layer in OSI model and it
can identify the Data link layer encapsulation of the packet only, the VLAN tag fi eld is
added into the Data Link Layer encapsulation for identifi cation.
In 1999 IEEE ratifi ed the IEEE 802.1Q protocol to standardize VLAN implementation,
defi ning the structure of VLAN-tagged packets. IEEE 802.1Q protocol defi nes that a
4-byte VLAN tag is encapsulated after the Destination MAC Address and Source MAC
Address to identify the VLAN membership of the packet.
As shown in the following fi gure, a VLAN tag contains four fi elds, including TPID (Tag
Protocol Identifi er), Priority, CFI (Canonical Format Indicator), and VLAN ID.
Figure 6-2 Format of VLAN Tag
„
TPID: TPID is a 16-bit fi eld, indicating that this Data frame is VLAN-tagged. (By default
it is set to 0x8100 or no VLAN ID.)
„
Priority: Priority is a 3-bit fi eld related to 802.1p priority. Refer to the QoS section of
the users guide for more details.
„
CFI: CFI is a 1-bit fi eld, indicating whether the MAC address is encapsulated in
the standard format or modifi ed format. This fi eld is not described in detail in
this chapter.
„
VLAN ID: VLAN ID is a 12-bit fi eld indicating the ID of the VLAN to which this packet
belongs. It has a range of 0 to 4,095. IDs 0 and 4,095 are not used leaving the valid
entries for the fi eld in the range of 1 to 4,094.
The VLAN ID identifi es the VLAN to which a packet belongs. When the Switch
receives an untagged packet, it will encapsulate a VLAN tag with the default VLAN ID
of the Ingress Port, the packet will be assigned to the default VLAN of the Ingress
Port for transmission.