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VLAN Memberships

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Now let's get back to that "because of switches, we don't need routers

anymore" misconception. In Figure 6.4, notice that there are seven VLANs
or broadcast domains, counting VLAN 1. The nodes within each VLAN can
communicate with each other, but not with anything in a different VLAN,
because the nodes in any given VLAN "think" that they're actually in a
collapsed backbone as in Figure 6.3.

And what handy little tool do we need to enable the hosts in Figure 6.3 to

communicate to a node or host on a different network? You guessed it--a
router! Those nodes positively need to go through a router, or some other
layer-3 device, just like when they're configured for VLAN communication
(as shown in Figure 6.4). It's the same as if we were trying to connect differ-
ent physical networks. Communication between VLANs must go through a
layer-3 device. So don't expect routers to disappear anytime soon!

VLAN Memberships

LANs are usually created by an administrator, who then assigns

switch ports to each VLAN. Such a VLAN is called a

static VLAN

. If the

administrator wants to do a little more work up front and assign all the host
devices' hardware addresses into a database, the switches can be configured
to assign VLANs dynamically whenever a host is plugged into a switch.

Static VLANs

Static VLANs are the usual way of creating VLANs, and they're also the
most secure. The switch port that you assign a VLAN association to always
maintains that association until an administrator manually changes that port
assignment.

This type of VLAN configuration is comparatively easy to set up and

monitor, and it works well in a network where the movement of users within
the network is controlled. And, although it can be helpful to use network
management software to configure the ports, it's not mandatory.

In Figure 6.4, each switch port was configured with a VLAN membership

by an administrator based on which VLAN the host needed to be a member
of--the device's actual physical location doesn't matter. The broadcast
domain the hosts will become a member of is an administrative choice.

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