9032579-03 Virtual LANs (VLANs) 85
VLAN Egress Ports
The VLAN Egress Ports parameter is used to assign ports to a VLAN for
carrying VLAN tagged frames across a network. The assignment of
egress ports does not affect the assignment of VLAN IDs to frames
entering the switch. However, frames exiting the switch may be sent out
the egress ports configured for a specific VLAN ID. Frames exiting the
switch via egress ports for a given VLAN are normally tagged.
VLAN Access Ports
Individual ELS100-24TX ports can be configured as one of two types for
the purpose of VLAN configuration: Access or Hybrid. A VLAN Access
port is used to connect one or more VLAN-unaw are devic es to the s witch.
VLAN tagged frames are not allowed to enter or exit an Access port. If a
tagged frame enters the switch on an Access port, the switch will drop the
frame. End-user stations which do not support 802.1Q tags should be
attached to ports on the switch configured as Access ports.
In Example 1 in Figure D-2, both ports are designated as Access ports.
The ports are both configured to be on VLAN X. An untagged frame (1)
comes in through the left port and gets tagged with a VLAN X tag (2),
based on the incoming port PVID. As the frame exits through the right
port, the tag is stripped (3) since the outgoing port is an Access port as
well and can only transmit untagged frames. The frame can propagate
through the switch in this example only because both ports are on the
same VLAN.
In Example 2 in Figure D-2 , both ports are also Acc ess ports, however the
port on the left is on VLAN X while the port on the right on VLAN Y. The
untagged frame (1) comes in through the left por t and aga i n gets tagged
with a VLAN X tag (2). However, because the outgoing port is on a
different VLAN (VLAN Y), the fr ame is dropped. In ge neral, fr ames can not
propagate between ports unless both ports belong to the same VLAN.
Figure D-2. VLAN Access Ports