User's Manual

User’s Manual of SGS-5240 Series Managed Switch
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An interface cannot function as an edge port under the following conditions:
 If spanning tree mode is set to STP , edge-port mode cannot automatically transition to operational edge-port state
using the automatic setting.
 If loopback detection is enabled and a loopback BPDU is detected, the interface cannot function as an edge port
until the loopback state is released.
 If an interface is in forwarding state and its role changes, the interface cannot continue to function as an edge port
even if the edge delay time has expired.
 If the port does not receive any BPDUs after the edge delay timer expires, its role changes to designated port and it
immediately enters forwarding state.
 BPDU Guard – This feature protects edge ports from receiving BPDUs. It prevents loops by shutting down an edge port
when a BPDU is received instead of putting it into the spanning tree discarding state. In a valid configuration, configured
edge ports should not receive BPDUs. If an edge port receives a BPDU an invalid configuration exists, such as a
connection to an unauthorized device. The BPDU guard feature provides a secure response to invalid configurations
because an administrator must manually enable the port.
(Default: Disabled)
 BPDU Filter – BPDU filtering allows you to avoid transmitting BPDUs on configured edge ports that are connected to end
nodes. By default, STA sends BPDUs to all ports regardless of whether administrative edge is enabled on a port. BDPU
filtering is configured on a per-port basis.
(Default: Disabled)
 Migration – If at any time the switch detects STP BPDUs, including Configuration or Topology Change Notification
BPDUs, it will automatically set the selected interface to forced STP-compatible mode. However, you can also use the
Protocol Migration button to manually re-check the appropriate BPDU format (RSTP or STP compatible) to send on the
selected interfaces. (Default: Disabled)
Switch Management > STP > STP-RSTP> Interface Status page is used to display the current status of ports or groups in the
Spanning Tree.
◆Spanning Tree – Shows if STA has been enabled on this interface.
◆BPDU Flooding – Shows if BPDUs will be flooded to other ports when spanning tree is disabled globally on the switch or
disabled on a specific port.
◆STA Status – Displays current state of this port within the Spanning Tree:
 Discarding - Port receives STA configuration messages, but does not forward packets.
 Learning - Port has transmitted configuration messages for an interval set by the Forward Delay parameter without
receiving contradictory information. Port address table is cleared, and the port begins learning addresses.
 Forwarding - Port forwards packets, and continues learning addresses.
 The rules defining port status are:
 A port on a network segment with no other STA compliant bridging device is always forwarding.
 If two ports of a switch are connected to the same segment and there is no other STA device attached to this
segment, the port with the smaller ID forwards packets and the other is discarding.
 All ports are discarding when the switch is booted, then some of them change state to learning, and then to
forwarding.
 Forward Transitions – The number of times this port has transitioned from the Learning state to the Forwarding state.
 Designated Cost – The cost for a packet to travel from this port to the root in the current Spanning Tree configuration.
The slower the media, the higher the cost.
 Designated Bridge – The bridge priority and MAC address of the device through which this port must communicate to
reach the root of the Spanning Tree.