Table of Contents
Advertisement
| VLAN Configuration
C
6
HAPTER
IEEE 802.1Q VLANs
VLAN Classification – When the switch receives a frame, it classifies the
frame in one of two ways. If the frame is untagged, the switch assigns the
frame to an associated VLAN (based on the default VLAN ID of the
receiving port). But if the frame is tagged, the switch uses the tagged
VLAN ID to identify the port broadcast domain of the frame.
Port Overlapping – Port overlapping can be used to allow access to
commonly shared network resources among different VLAN groups, such
as file servers or printers. Note that if you implement VLANs which do not
overlap, but still need to communicate, you can connect them by enabled
routing on this switch.
Untagged VLANs – Untagged (i.e., static) VLANs are typically used to
reduce broadcast traffic and to increase security. A group of network users
assigned to a VLAN form a broadcast domain that is separate from other
VLANs configured on the switch. Packets are forwarded only between ports
that are designated for the same VLAN. Untagged VLANs can be used to
manually isolate user groups or subnets. However, you should use IEEE
802.3 tagged VLANs with GVRP whenever possible to fully automate VLAN
registration.
Automatic VLAN Registration – GVRP (GARP VLAN Registration
Protocol) defines a system whereby the switch can automatically learn the
VLANs to which each end station should be assigned. If an end station (or
its network adapter) supports the IEEE 802.1Q VLAN protocol, it can be
configured to broadcast a message to your network indicating the VLAN
groups it wants to join. When this switch receives these messages, it will
automatically place the receiving port in the specified VLANs, and then
forward the message to all other ports. When the message arrives at
another switch that supports GVRP, it will also place the receiving port in
the specified VLANs, and pass the message on to all other ports. VLAN
requirements are propagated in this way throughout the network. This
allows GVRP-compliant devices to be automatically configured for VLAN
groups based solely on end station requests.
To implement GVRP in a network, first add the host devices to the required
VLANs (using the operating system or other application software), so that
these VLANs can be propagated onto the network. For both the edge
switches attached directly to these hosts, and core switches in the
network, enable GVRP on the links between these devices. You should also
determine security boundaries in the network and disable GVRP on the
boundary ports to prevent advertisements from being propagated, or
forbid those ports from joining restricted VLANs.
If you have host devices that do not support GVRP, you should
N
:
OTE
configure static or untagged VLANs for the switch ports connected to these
devices (as described in
"Adding Static Members to VLANs" on page
231).
But you can still enable GVRP on these edge switches, as well as on the
core switches in the network.
– 227 –
Advertisement
Chapters
Table of Contents
