Brocade Multi-Service IronWare Switching Configuration Gui Manual de usuario descargar pdf (Pagina 385)

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Multi-Service IronWare Switching Configuration Guide 355

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802.1s Multiple Spanning Tree Protocol

In the configuration above, all PVST BPDUs associated with VLAN 1 would be discarded. Since IEEE

BPDUs associated with VLAN 1 are untagged, they are discarded because the ports in VLAN 1 are

tagged. Effectively, the BPDUs are never processed by the Spanning Tree Protocol. STP assumes

that there is no better bridge on the network and sets the ports to FORWARDING. This could cause

a Layer 2 loop.

The following configuration is correct.

Brocade(config)# default-vlan-id 1000

Brocade(config)# vlan 1

Brocade(config-vlan-1)# tagged ethernet 1/1 to 1/2

Brocade(config-vlan-1)# exit

Brocade(config)# interface ethernet 1/1

Brocade(config-if-e10000-1/1)# pvst-mode

Brocade(config-if-e10000-1/1)# exit

Brocade(config)# interface ethernet 1/2

Brocade(config-if-e10000-1/2)# pvst-mode

Brocade(config-if-e10000-1/2)# exit

Setting the ports as dual-mode ensures that the untagged IEEE 802.1Q BPDUs reach the VLAN 1

instance.

802.1s Multiple Spanning Tree Protocol

Multiple Spanning Tree Protocol (MSTP) as defined in IEEE 802.1s allows you to configure multiple

STP instances. This will allow several VLANs to be mapped to a reduced number of spanning-tree

instances. This ensures loop-free topology for 1 or more VLANs that have the same Layer 2

topology.

NOTE

In addition to the features described in this chapter, Root Guard and BPDU Guard are supported.

Refer to “Root Guard” and “BPDU Guard” for details.

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. In addition, MSTP can coexist with individual devices running STP or RSTP in

the Common and Internal Spanning Trees instance (CIST). With the exception of the provisions for

multiple instances, MSTP operates exactly like RSTP.

For example, in Figure 66 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 RSTP 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.

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