92
C
HAPTER
6: S
PANNING
T
REE
P
ROTOCOL
(STP)
Figure 16
Multiple Spanning Tree Domains
When the switches in this configuration start up, STP configures each
STPD such that there are no active loops in the topology. STP could
configure the topology in a number of ways to make it loop-free.
In Figure 16
, the connection between Switch A and Switch B is put into
blocking state, and the connection between Switch Y and Switch Z is put
into blocking state. After STP converges, all the VLANs can communicate,
and all bridging loops are prevented.
The VLAN
Marketing
, which has not been assigned to either STPD1 or
STPD2, communicates using all five switches. The topology has no loops,
because STP has already blocked the port connection between Switch A
and Switch B, and between Switch Y and Switch Z.
Within a single STPD, you must be extra careful when configuring your
VLANs. Figure 17
illustrates a network that has been incorrectly set up
using a single STPD so that the STP configuration disables the ability of
the switches to forward VLAN traffic.
Sales, Personnel, Marketing
STPD 1 STPD 2
Manufacturing, Engineering, Marketing
Sales, Personnel, Manufacturing, Engineering, Marketing
Switch A Switch Y
Switch Z
Switch M
Switch B
91_009
