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DES-1210G Fast Ethernet/Gigabit Ethernet Switch User's Guide
Port-based VLANs
The DES-1210G supports up to 9 port-based VLANs. Port-based VLANs limit traffic that flows
into and out of switch ports. Thus, all devices connected to a port are members of the VLAN(s)
the port belongs to, whether there is a single computer directly connected to a switch, or an entire
department.
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 it's 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
groups. Setting VLAN 1 members are port 1,2,3,4 and VLAN 2 members are 1,5,6,7. The Port 1 is
belonging to two VLAN groups. The port 8, 9, 10 are not configured to any VLAN group. This is
means port 8,9,10 are 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 applied to the other member ports.
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