Cabletron Systems SmartSTACK ELS100-24TXM Installation And User Manual page 107

In Example 3 in Figure D-3B, an untagged frame arrives at the left port
(1). The switch tags the frame with the PVID for VLAN X (2). Since the
destination MAC address has already been learned as a tagged station
on VLAN X on the outgoing port, the frame is sent out with a VLAN X tag.
Example 4 in Figure D-3B is similar to Example 3 except that both ports
(incoming and outgoing) have a VLAN X PVID. The untagged frame
arrives at the incoming port (1) and gets tagged with a VLAN X tag (2).
The tag may or may not be stripped off as the frame exits the switch,
depending on how the MAC address of the destination device was
learned (3). In this example, the destination was learned as an untagged
station so the tag is stripped. This Hybrid port example is thus essentially
the same as the Access port case in Figure D-2, Example 1.
When sending broadcast or unknown DA unicast frames
out a Hybrid port, the frames are always tagged. The
VLAN ID of the tag is identical to the VLAN ID that was as-
signed to the frame when it entered the switch on the
source port.
Figure D-3B. VLAN Hybrid Ports (Examples 3 and 4)
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