Owner's Manual

Chapter 18. STP | 539
NETGEAR 8800 User Manual
• Engineering is the carrier VLAN on STPD2.
• Marketing is a member of both STPD1 and STPD2 and is a protected VLAN.
Figure 35. Multiple STPDs
When the switches in this configuration boot-up, STP configures each STPD such that the
topology contains no active loops. STP could configure the topology in a number of ways to
make it loop-free.
In Figure 35, 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 protected VLAN Marketing, which has been assigned to both STPD1 and 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 36
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 Y
Switch Z
Switch M
Switch B
EX_048
Switch A