Specifications

8-16 Rapier Switch Software Reference
Software Release 2.7.3
C613-03098-00 REV A
Figure 8-1: Format of user priority and VLAN data in an Ethernet frame
Ethernet packets that contain a VLAN tag are referred to as tagged frames, and
switch ports that transmit tagged frames are referred to as tagged ports.
Ethernet packets that do not contain a VLAN tag are referred to as untagged
frames, and switch ports that transmit untagged frames are referred to as
untagged ports. VLANs can consist of simple logical groupings of untagged
ports in which the ports receive and transmit untagged packets. Alternatively,
VLANs can contain only tagged ports or a mixture of tagged and untagged
ports.
The switch is VLAN-aware. It can accept VLAN tagged frames, and supports
the VLAN switching required by such tags. A network can contain a mixture of
VLAN-aware devices, for example, other 802.1q-compatible switches, and
VLAN-unaware devices, for example, workstations and legacy switches that
do not support VLAN tagging. The switch can be configured to send VLAN
tagged or untagged frames on each port, depending on whether the devices
connected to the port are VLAN-aware. By assigning a port to two different
VLANs, to one as an untagged port and to another as a tagged port, it is
possible for the port to transmit both VLAN-tagged and untagged frames. A
port must belong to a VLAN at all times unless the port has been set as the
mirror port for the switch.
Every frame admitted by the switch has a VID associated with it. When a frame
arrives on a tagged port, the associated VID is determined from the VLAN tag
the frame had when it arrived. When a frame arrives on an untagged port, it is
Table 8-3: Reserved VID values
VID value (hexadecimal) Meaning and use of reserved VID values
0 The null VLAN ID. Indicates that the tag header contains only
user priority information; no VLAN Identifier is present in the
frame. This VID value must not be configured in any forwarding
database entry, or used in any management operation. Frames
that contain the null VLAN ID are also known as priority-tagged
frames.
1 The default VID value used for classifying frames on ingress
through an untagged switch port.
FFF Reserved for implementation use. This VID value must not be
configured in any forwarding database entry, used in any
management operation, or transmitted in a tag header.
TPID
16 bits
1 bit
3 bits
12 bits
User
Priority
CFI VID
0x81-00
Preamble
Destination
Address
Source
Address
Type/
Length
Frame Data
CRC
64 bits
48 bits 48 bits
16
bits
368-12000
32 bits
SWITCH6