D-Link DES-2108/E [54/199] Vlan segmentation

24-port NWay Ethernet Switch User’s Guide

40 Switch Management

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.

There are two key components to understanding port-based

VLANs; Port VLAN ID numbers (PVID) and VLAN ID numbers

(VID). Both variables are assigned to a switch port, but there are

important differences between them. A user can only assign one

PVID to each switch port. The PVID defines which VLAN a switch

will forward packets from the connected segment on, when packets

need to be forwarded to another switch port or somewhere else on

the network. On the other hand, a user can define a port as a

member of multiple VLANs (VIDs), allowing the segment connected

to it to receive packets from many VLANs on the network. These

two variables control a port’s ability to transmit and receive VLAN

traffic, and the difference between them provides network

segmentation, while still allowing resources to be shared across

more than one VLAN.

VLAN Segmentation

Take for example a packet that is transmitted by a machine on Port

1 that is a member of VLAN 2 and has the Port VLAN ID number 2

(PVID=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

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