CHAPTER 2 | Network
Planning
Application
Examples
MAKING VLAN
C
ONNECTIONS
These switches support VLANs which can be used to
organize
any
group of
network nodes into separate broadcast domains. VLANs confine broadcast traffic
to the originating group,
and
can
eliminate broadcast storms in large networks.
This provides a more secure and cleaner network environment.
VLANs can be based on untagged port groups, or traffic can be explicitly tagged
to identify the VLAN group to which it belongs. Untagged VLANs can be used for
small networks attached to a single switch. However, tagged VLANs should be
used for larger networks, and all the VLANs assigned to the inter-switch links.
These switches also support multiple spanning trees which allow VLAN groups to
maintain a more stable path between all VLAN members. This can reduce the
overall amount of protocol traffic crossing the network, and provide a shorter
reconfiguration
time
if any link in the spanning tree fails.
At Layer 3, VLANs are used to create an IP interface, where one or more ports
are assigned to the same IP segment. Traffic is automatically routed between
different IP segments on
the
same
switch, without any need to configure routing
protocols.
Figure 10: Making VLAN Connections
R&D
VLAN
2
VLAN 1
Tagged
Ports
Finance
Untagged
Por
t
s
VLAN
unaware
switch
Tagged
Por
t
VLAN
aware
switch
Te s ti n g
R&D
Marke
t
ing
Finance
T
esting
VLAN
3
VLAN
4
VLAN 3
VLAN 1
VLAN 2
N
OTE: When connecting to a switch that does not support IEEE
802.1Q VLAN tags, use untagged ports.
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