Radiance 10/100 Mbps Services Line Card
48
Traffic Filtering and Forwarding Over the Access Port
The only frames that are forwarded from the trunk port to the access port
are the following:
•
Untagged Layer 2 control protocols frames. Untagged L2CP are
forwarded transparently, however, they may be discarded on a per-
protocol basis.
•
Tagged frames containing the PVID. These frames are forwarded as
untagged frames (i.e., the PVID is removed).
•
Tagged frames containing one of the configured user VLANs.
Tagged frames containing an acceptable user VLAN are forwarded
without modifications, unless untagging has been enabled. The R821
provides an option to forward frames untagged on a per-VLAN basis. For
example, if the configured user VLANs are 10-25, the access port may
be configured to untag frames for VLANs 10 and 11. Tagged frames,
whose VLANs are 10 or 11, will then be forwarded over the access port
as untagged frames. Tagged frames, whose VLANs are 12-25, will be
forwarded without any modifications, as shown in the illustration below.
The illustration also displays how different types of frames arriving at the
trunk port are processed in 802.1Q mode.
R821
Access
Port
Trunk
Port
IEEE 802.1Q Mode
tagged
untagged
tagged
PVID = 2
user VLAN
= 10-25
tagged
dropped
25
25
26
priority-tagged
0
0
26
untag = 10 & 11
tagged
11
untagged
untagged
tagged
priority-tagged
untagged L2CP
untagged L2CP
untagged
tagged w/PVID
2