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DES-3550 Fast Ethernet Layer 2 Switch
On port-based VLANs, NICs do not need to be able to identify 802.1Q tags in packet headers. NICs send and receive
normal Ethernet packets. If the packet's destination lies on the same segment, communications take place using normal
Ethernet protocols. Even though this is always the case, when the destination for a packet lies on another switch port,
VLAN considerations come into play to decide if the packet gets dropped by the Switch or delivered.
VLAN Segmentation
Take for example a packet that is transmitted by a machine on Port 1 that is a member of VLAN 2. If the destination lies on
another port (found through a normal forwarding table lookup), the Switch then looks to see if the other port (Port 10) is a
member of VLAN 2 (and can therefore receive VLAN 2 packets). If Port 10 is not a member of VLAN 2, then the packet
will be dropped by the Switch and will not reach its destination. If Port 10 is a member of VLAN 2, the packet will go
through. This selective forwarding feature based on VLAN criteria is how VLANs segment networks. The key point being
that Port 1 will only transmit on VLAN 2.
Network resources such as printers and servers however, can be shared across VLANs. This is achieved by setting up
overlapping VLANs. That is ports can belong to more than one VLAN group. For example, setting VLAN 1 members to
ports 1, 2, 3, and 4 and VLAN 2 members to ports 1, 5, 6, and 7. Port 1 belongs to two VLAN groups. Ports 8, 9, and 10
are not configured to any VLAN group. This means ports 8, 9, and 10 are in the same VLAN group.
VLAN and Trunk Groups
The members of a trunk group have the same VLAN setting. Any VLAN setting on the members of a trunk group will
apply to the other member ports.
NOTE: In order to use VLAN segmentation in conjunction with port trunk
groups, you can first set the port trunk group(s), and then you may
configure VLAN settings. If you wish to change the port trunk grouping
with VLANs already in place, you will not need to reconfigure the VLAN
settings after changing the port trunk group settings. VLAN settings will
automatically change in conjunction with the change of the port trunk
group settings.
Static VLAN Entry
In the Configuration folder, open the VLAN folder and click the Static VLAN Entry link to open the following window:
Figure 6- 36. Current 802.1Q Static VLANs Entries window
The 802.1Q Static VLANs menu lists all previously configured VLANs by VLAN ID and VLAN Name. To delete an
existing 802.1Q VLAN, click the corresponding
button under the Delete heading.
To create a new 802.1Q VLAN, click the Add button in the 802.1Q Static VLANs menu. A new menu will appear, as
shown below, to configure the port settings and to assign a unique name and number to the new VLAN. See the table
below for a description of the parameters in the new menu.
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