Dell PowerConnect FCS624S Configuration Guide - Page 330

8 802.1s Multiple Spanning Tree Protocol Syntax: show errdisable summary Errdisable Syslog messages When the system places a port into an errdisabled state for BPDU guard, a log message is generated. When the errdisable recovery timer expires, a log message is also generated. A Syslog message such as the following is generated after a port is placed into an errdisable state for BPDU guard. STP: VLAN 50 BPDU-guard port 3 detect (Received BPDU), putting into err-disable state A Syslog message such as the following is generated after the recovery timer expires. ERR_DISABLE: Interface ethernet 3, err-disable recovery timeout 802.1s Multiple Spanning Tree Protocol Multiple Spanning Tree Protocol (MSTP), as defined in IEEE 802.1s, allows multiple VLANs to be managed by a single STP instance and supports per-VLAN STP. As a result, several VLANs can be mapped to a reduced number of spanning-tree instances. This ensures loop-free topology for one or more VLANs that have the similar layer-2 topology. The Dell implementation supports up to 16 spanning tree instances in an MSTP enabled bridge which means that it can support up to 16 different Layer 2 topologies. The spanning tree algorithm used by MSTP is RSTP which provides quick convergence. Multiple spanning-tree regions Using MSTP, the entire network runs a common instance of RSTP. Within that common instance, one or more VLANs can be individually configured into distinct regions. The entire network runs the common spanning tree instance (CST) and the regions run a local instance. The local instance is known as Internal Spanning Tree (IST). The CST treats each instance of IST as a single bridge. Consequently, ports are blocked to prevent loops that might occur within an IST and also throughout the CST. With the exception of the provisions for multiple instances, MSTP operates exactly like RSTP. For example, in Figure 56 a network is configured with two regions: Region 1 and Region 2. The entire network is running an instance of CST. Each of the regions is running an instance of IST. In addition, this network contains Switch 1 running MSTP that is not configured in a region and consequently is running in the CIST instance. In this configuration, the regions are each regarded as a single bridge to the rest of the network, as is Switch 1. The CST prevents loops from occurring across the network. Consequently, a port is blocked at port 1/2 of switch 4. Additionally, loops must be prevented in each of the IST instances. Within the IST Region 1, a port is blocked at port 1/2 of switch 4 to prevent a loop in that region. Within Region 2, a port is blocked at port 3/2 of switch 3 to prevent a loop in that region. 288 PowerConnect B-Series FCX Configuration Guide 53-1002266-01