Port-Based Vlans - D-Link DES-3624 Series User Manual
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Stackable NWay Ethernet Switch User's Guide
Figure 5-5. Data transmissions between 802.1Q-compliant Switches
In the above example, step 4 is the key element. Because the packet has 802.1Q VLAN data encoded in its
header, the ingress port can make VLAN-based decisions about its delivery: whether server #2 is attached to
a port that is a member of VLAN 2 and, thus, should the packet be delivered; the queuing priority to give to
the packet, etc. It can also perform these functions for VLAN 1 packets as well, and, in fact, for any tagged
packet it receives regardless of the VLAN number.
If the ingress port in step 4 were connected to a non-802.1Q-compliant device and was thus receiving
untagged packets, it would tag its own PVID onto the packet and use this information to make forwarding
decisions. As a result, the packets coming from the non-compliant device would automatically be placed on
the ingress ports VLAN and could only communicate with other ports that are members of this VLAN.
Port-Based VLANs
Port-based VLANs are a simplified version of the 802.1Q VLANs described in the previous section. In port-
based VLANs, all the 802.1Q settings are pre-configured allowing you to quickly and easily setup and
maintain port-based VLANs on your network.
In port-based VLANs, broadcast, multicast and unknown packets will be limited to within the VLAN. Thus,
port-based VLANs effectively segment your network into broadcast domains. Furthermore, ports can only
belong to a single VLAN.
Because port-based VLANs are uncomplicated and fairly rigid in their implementation, they are best used for
network administrators who wish to quickly and easily setup VLANs in order to isolate limit the effect of
broadcast packets on their network.
For the most secure implementation, make sure that end stations are directly connected to the switch.
Attaching a hub, switch or other repeater to the port causes all stations attached to the repeater to become
members of the Port-based VLAN.
40
Switch Management Concepts
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