Owner's Manual

540 | Chapter 18. STP
NETGEAR 8800 User Manual
Figure 36. Incorrect Tag-Based STPD Configuration
The tag-based network in Figure 36 has the following configuration:
• Switch 1 contains VLAN Marketing and VLAN Sales.
• Switch 2 contains VLAN Engineering and VLAN Sales.
• Switch 3 contains VLAN Marketing, VLAN Engineering, and VLAN Sales.
• The tagged trunk connections for three switches form a triangular loop that is not
permitted in an STP topology.
• All VLANs in each switch are members of the same STPD.
STP can block traffic between switch 1 and switch 3 by disabling the trunk ports for that
connection on each switch.
Switch 2 has no ports assigned to VLAN Marketing. Therefore, if the trunk for VLAN
Marketing on switches 1 and 3 is blocked, the traffic for VLAN Marketing will not be able to
traverse the switches.
Note: If an STPD contains multiple VLANs, all VLANs should be
configured on all ports in that domain, except for ports that connect
to hosts (edge ports).
Multiple STPDs on a Port
Traditional 802.1D STP has some inherent limitations when addressing networks that have
multiple VLANs and multiple STPDs. For example, consider the sample depicted in
Figure 37.
Marketing & Sales Marketing, Sales & Engineering
Switch 1 Switch 3
Switch 2
EX_049
Sales & Engineering