Nortel 8300 User Manual page 23

802.1Q tagged ports
Tagging a frame adds four octets to a frame, making it bigger than the
traditional maximum frame size. These frames are sometimes referred to
as "baby giant" frames. If a device does not support IEEE 802.1Q tagging,
it can have problems interpreting tagged frames and receiving baby giant
frames.
In the ERS 8300, your port level configuration determines whether tagged
frames are sent and received. Tagging is set as true or false for the port and
is applied to all VLANs on that port.
When you enable tagging on an untagged port, the port's previous
configuration of VLANs and STGs is lost. In addition, the port resets and
runs Spanning Tree Protocol, thus breaking connectivity while the protocol
goes through the normal listening and learning states before the forwarding
state.
A ERS 8300 port with tagging enabled sends frames explicitly tagged with a
VLAN ID. Tagged ports are typically used to multiplex traffic belonging to
multiple VLANs to other IEEE-802.1Q-compliant devices.
If tagging is disabled on a ERS 8300 port, it does not send tagged frames.
A nontagged port connects the ERS 8300 to devices that do not support
IEEE 802.1Q tagging. If a tagged frame is forwarded out a port on which
tagging is set to false, the switch removes the tag from the frame before
sending it out the port.
If a port is set for tagging on a ERS 8300, and the port is also a member of
an untagged multilink trunk (MLT), or the reverse is true. The port settings
on the MLT overrides.
Treatment of tagged and untagged frames
A ERS 8300 associates a frame with a VLAN based on the data content of
the frame and the configuration of the destination port. Whether the frame
is tagged or untagged dictates how that frame is treated.
If a tagged frame is received on a tagged port, with a VLAN ID specified in
the tag, the ERS 8300 directs it to that VLAN, if it is present.
For untagged frames, VLAN membership is implied from the content of
the frame itself. For untagged frames received on a tagged port, you can
configure the port to either discard or accept the frame. If you configure
a tagged port to accept untagged frames, the port must be assigned to
a port-based VLAN.
On the ERS 8300 you have the option to configure tagged ports to send
untagged frames on the default VLAN of the port.
Configuration — VLANs, Spanning Tree, and Static Link Aggregation using Device Manager
Copyright © 2005-2007, Nortel Networks
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Nortel Ethernet Routing Switch 8300
NN46200-510 03.01 Standard
4.0 27 August 2007
VLANs 23