2-4
Static Virtual LANs (VLANs)
Port-Based Virtual LANs (Static VLANs)
bandwidth is saved by not allowing packets to flood out all ports. Separate
VLANs on the switch can communicate with each other through an external
router.
For example, referring to figure 2-1, if ports A1 through A4 belong to VLAN_1
and ports A5 through A8 belong to VLAN_2, traffic from end-node stations on
ports A2 through A4 is restricted to only VLAN_1, while traffic from ports A5
through A7 is restricted to only VLAN_2. For nodes on VLAN_1 to communi-
cate with VLAN_2, their traffic must go through an external router via ports
A1 and A8.
Figure 2-1. Example of Routing Between VLANs via an External Router
Overlapping (Tagged) VLANs. A port on the switch can be a member of
more than one VLAN if the device to which it is connected complies with the
802.1Q VLAN standard. For example, a port connected to a central server using
a network interface card (NIC) that complies with the 802.1Q standard can be
a member of multiple VLANs, allowing members of multiple VLANs to use the
server. Although these VLANs cannot communicate with each other through
the server, they can all access the server over the same connection from the
switch. Where VLANs overlap in this way, VLAN “tags” are used to distinguish
between traffic from different VLANs.
External
Router
VLAN_2
VLAN_1
Port A1
Port A8
Port A2
Port A3
Port A4
Port A5
Port A6
Port A7
Switch with Two
VLANs Configured
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