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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 destination 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
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 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.
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, first set the
port trunk group(s), and then configure the VLAN settings. To change the port trunk grouping
with VLANs already in place it is unnecessary 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.
Protocol VLANs
®
The xStack
DGS–3426G incorporates the idea of protocol-based VLANs. This standard, defined by the IEEE 802.1v standard
maps packets to protocol-defined VLANs by examining the type octet within the packet header to discover the type of protocol
associated with it. After assessing the protocol, the Switch will forward the packets to all ports within the protocol-assigned
VLAN. This feature will benefit the administrator by better balancing load sharing and enhancing traffic classification. The
®
xStack
DGS-3426G Layer 2 Gigabit Ethernet Managed Switch
Table 3 - 1 VLAN Example – Assigned Ports
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
108
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