Brocade Communications Systems Brocate Ethernet Access Switch 6910 - Manual (Page 813)

Brocade 6910 Ethernet Access Switch Configuration Guide 763
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Configuring Global Settings for STA
36
Configuring Global Settings for STA
Use the Spanning Tree > STA (Configure Global - Configure) page to configure global settings for the
spanning tree that apply to the entire switch.
CLI References
• “Spanning Tree Commands” on page 333
Command Usage
• Spanning Tree Protocol 14
This option uses RSTP set to STP forced compatibiltiy mode. It uses RSTP for the internal state
machine, but sends only 802.1D BPDUs. This creates one spanning tree instance for the entire
network. If multiple VLANs are implemented on a network, the path between specific VLAN
members may be inadvertently disabled to prevent network loops, thus isolating group
members. When operating multiple VLANs, we recommend selecting the MSTP option.
• Rapid Spanning Tree Protocol
14
RSTP supports connections to either STP or RSTP nodes by monitoring the incoming protocol
messages and dynamically adjusting the type of protocol messages the RSTP node transmits,
as described below:
• STP Mode – If the switch receives an 802.1D BPDU (i.e., STP BPDU) after a port’s
migration delay timer expires, the switch assumes it is connected to an 802.1D bridge and
starts using only 802.1D BPDUs.
• RSTP Mode – If RSTP is using 802.1D BPDUs on a port and receives an RSTP BPDU after
the migration delay expires, RSTP restarts the migration delay timer and begins using
RSTP BPDUs on that port.
• Multiple Spanning Tree Protocol
MSTP generates a unique spanning tree for each instance. This provides multiple pathways
across the network, thereby balancing the traffic load, preventing wide-scale disruption when a
bridge node in a single instance fails, and allowing for faster convergence of a new topology for
the failed instance.
• To allow multiple spanning trees to operate over the network, you must configure a related
set of bridges with the same MSTP configuration, allowing them to participate in a specific
set of spanning tree instances.
• A spanning tree instance can exist only on bridges that have compatible VLAN instance
assignments.
• Be careful when switching between spanning tree modes. Changing modes stops all
spanning-tree instances for the previous mode and restarts the system in the new mode,
temporarily disrupting user traffic.
14. STP and RSTP BPDUs are transmitted as untagged frames, and will cross any VLAN boundaries.