Default Vlans; Vlan Segmentation - D-Link DES-6500 User Manual

D-Link DES-6500 Layer 3 Stackable Gigabit Ethernet Switch
reception. This eliminates the subsequent processing of packets that will just be dropped by
the destination port.

Default VLANs

The Switch initially configures one VLAN, VID = 1, called "default." The factory default
setting assigns all ports on the Switch to the "default." As new VLANs are configured in Port-
based mode, their respective member ports are removed from the "default."
Packets cannot cross VLANs. If a member of one VLAN wants to connect to another VLAN,
the link must be through an external router.
Note: If no VLANs are configured on the switch, then all
packets will be forwarded to any destination port. Packets with
unknown source addresses will be flooded to all ports.
Broadcast and multicast packets will also be flooded to all
ports.
An example is presented below:
VLAN Name
System (default)
Engineering
Marketing
Finance
Sales

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.
VID Switch Ports
1 5, 6, 7, 8, 21, 22, 23, 24
2 9, 10, 11, 12
3 13, 14, 15, 16
4 17, 18, 19, 20
5 1, 2, 3, 4
Table 4- 1. VLAN Example – Assigned Ports
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