Functions and Features Supported on Enterasys Devices
Fixed Switch Configuration Guide 15-7
Disabling Spanning Tree
Spanning Tree may be disabled globally or on a per port basis. If Spanning Tree is disabled
globally all linked ports will be in a forwarding state and the Spanning Tree Protocol will not run.
Additionally, a received BPDU will be treated as any multicast packet and flooded out all ports.
If Spanning Tree is disabled on a port by setting portadmin to disabled using the set spantree
portadmin command, the port will be in a forwarding state and the protocol will not run for that
port. A received BPDU will be consumed. The intention is that the port terminates the Spanning
Tree domain. For instance, the port may be attached to a router. If this port were accidentally
attached to another switching port, a data loop may result.
STP Features
Enterasys switching devices provide seamless Spanning Tree functionality by:
• Creating a single Spanning Tree from any arrangement of switching or bridging elements.
• Compensating automatically for the failure, removal, or addition of any switching device in
an active data path.
• Achieving port changes in short time intervals, which establishes a stable active topology
quickly with minimal network disturbance.
• Using a minimum amount of communications bandwidth to accomplish the operation of the
Spanning Tree Protocol.
• Reconfiguring the active topology in a manner that is transparent to stations transmitting and
receiving data packets.
• Managing the topology in a consistent and reproducible manner through the use of Spanning
Tree Protocol parameters.
• Increasing security and reliability with SpanGuard, as described below and in
“Understanding and Configuring SpanGuard” on page 15-29.
• Further protecting your network from loop formation with Loop Protect, as described below
and in “Understanding and Configuring Loop Protect” on page 15-31.
• Supporting more port density and faster port speeds as described in “Updated 802.1t” on
page 15-8
SpanGuard
The Enterasys SpanGuard feature helps protect your network from two situations that can cause a
Denial of Service (DoS) condition: repeated topology change notifications and an unwanted
bridge being inserted into and forcing traffic through the topology. SpanGuard increases security
and reliability by preventing Spanning Tree respans that can occur when BPDUs are received on
user ports and notifies network management that they were attempted.
If a SpanGuard enabled port receives a BPDU, it becomes locked and transitions to the blocking
state. It will only transition out of the blocking state after a globally specified time or when it is
manually unlocked. By default, SpanGuard is globally disabled on stackable and standalone fixed
switch devices and must be globally enabled to operate on all user ports. For a more detailed
discussion of the SpanGuard feature, refer to “Understanding and Configuring SpanGuard” on
page 15-29.
Loop Protect
The Loop Protect feature prevents or short circuits loop formation caused by redundant paths in
your network by requiring ports to receive BPDUs (RSTP/MSTP only) on point-to-point ISLs
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