Spanning Tree Algorithm
108
Instruction Manual - NXA-ENET8-POE+
Configuring Interface Settings for STA
Use the Spanning Tree > STA (Configure Interface - Configure) page to configure RSTP and MSTP attributes for specific interfaces,
including port priority, path cost, link type, and edge port. You may use a different priority or path cost for ports of the same media
type to indicate the preferred path, link type to indicate a point-to- point connection or shared-media connection, and edge port to
indicate if the attached device can support fast forwarding. (References to "ports" in this section means "interfaces", which
includes both ports and trunks.)
The following table lists the options on this page:
Spanning Tree - STA Options
Interface
Displays a list of ports or trunks.
Spanning Tree
Enables/disables STA on this interface. (Default: Enabled)
When spanning tree is enabled globally (Configuring Global Settings for STA) or enabled on an
interface by this command, loopback detection is disabled.
BPDU Flooding
Enables/disables the flooding of BPDUs to other ports when global spanning tree is disabled (page
169) or when spanning tree is disabled on a specific port. When flooding is enabled, BPDUs are
flooded to all other ports on the switch or to all other ports within the receiving port's native VLAN
as specified by the Spanning Tree BPDU Flooding attribute (page 169). (Default: Enabled)
Priority
Defines the priority used for this port in the Spanning Tree Protocol. If the path cost for all ports
on a switch are the same, the port with the highest priority (i.e., lowest value) will be configured as
an active link in the Spanning Tree. This makes a port with higher priority less likely to be blocked if
the Spanning Tree Protocol is detecting network loops. Where more than one port is assigned the
highest priority, the port with lowest numeric identifier will be enabled.
• Default: 128
• Range: 0-240, in steps of 16
Admin Path Cost
This parameter is used by the STA to determine the best path between devices. Therefore, lower
values should be assigned to ports attached to faster media, and higher values assigned to ports
with slower media. Note that path cost takes precedence over port priority. (Range: 0 for auto-
configuration, 1-65535 for the short path cost method*, 1-200,000,000 for the long path cost
method)
By default, the system automatically detects the speed and duplex mode used on each port, and
configures the path cost according to the values shown below. Path cost "0" is used to indicate
auto-configuration mode. When the short path cost method is selected and the default path cost
recommended by the IEEE 8021w standard exceeds 65,535, the default is set to 65,535.
See the Recommended STA Path Cost Range table on page 109 and the Default STA Path
Costs table on page 110 for more information.
* - Refer to the
Configuring Global Settings for STA
section on page 104 for information on setting
the path cost method.The range displayed on the STA interface configuration page shows the
maximum value for path cost. However, note that the switch still enforces the rules for path cost
based on the specified path cost method (long or short)
Admin Link Type
The link type attached to this interface.
• Point-to-Point - A connection to exactly one other bridge.
• Shared - A connection to two or more bridges.
• Auto - The switch automatically determines if the interface is attached to a point-to-point link or
to shared media. (This is the default setting.)
Root Guard
STA allows a bridge with a lower bridge identifier (or same identifier and lower MAC address) to
take over as the root bridge at any time. Root Guard can be used to ensure that the root bridge is
not formed at a suboptimal location. Root Guard should be enabled on any designated port
connected to low-speed bridges which could potentially overload a slower link by taking over as
the root port and forming a new spanning tree topology. It could also be used to form a border
around part of the network where the root bridge is allowed. (Default: Disabled)