Filter
Top Products
xStack
®
DES-3200-10/18/28/28F Layer 2 Ethernet Managed Switch User Manual
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 VID Switch Ports
System (default) 1 5, 6, 7, 8, 21, 22, 23, 24
Engineering 2 9, 10, 11, 12
Marketing 3 13, 14, 15, 16
Finance 4 17, 18, 19, 20
Sales 5 1, 2, 3, 4
Table 3 - 1. VLAN Example - Assigned Ports
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.
Network resources 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, by setting VLAN 1 members to ports 1, 2, 3 and 4 and VLAN 2
members to ports 1, 5, 6 and 7, Port 1 will belong 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.
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, you can first
set the port trunk group(s), and then you may configure VLAN settings. If you wish to change
the port trunk grouping with VLANs already in place, you will not need 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.
Q-in-Q VLANs
Q-in-Q VLANs (also sometimes referred to as double VLANs) allow network providers to expand their VLAN
configurations to place customer VLANs within a larger inclusive VLAN, which adds a new layer to the VLAN
configuration. This basically lets large ISP's create L2 Virtual Private Networks and also create transparent LANs for
their customers, which will connect two or more customer LAN points without over-complicating configurations on the
client's side. Not only will over-complication be avoided, but also now the administrator has over 4000 VLANs in which
62