Extreme Networks ExtremeWare XOS 10.1, Manual

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150 ExtremeWare XOS 10.1 Concepts Guide
Spanning Tree Protocol (STP)
When RSTP stabilizes, all:
• Root ports and designated ports are in the forwarding state
• Alternate ports and backup ports are in the blocking state
RSTP makes the distinction between the alternate and backup port roles to describe the rapid transition
of the alternate port to the forwarding state if the root port fails.
Ports that connect to non-STP devices are edge ports. Edge ports do not participate in RSTP, and their
role is not confirmed. Edge ports immediately enter the forwarding state.
Link Types
You can configure the link type of a port in an STPD. RSTP tries to rapidly move designated
point-to-point links into the forwarding state when a network topology change or failure occurs. For
rapid convergence to occur, the port must be configured as a point-to-point link.
Table 30 describes the link types.
Configuring Link Types. By default, all ports are broadcast links. To configure the ports in an STPD,
use the following command:
configure stpd <stpd_name> ports link-type [auto | edge | broadcast | point-to-point]
<port_list>
•
auto
—Configures the ports as auto links. If the link is in full duplex mode, or if link aggregation is
enabled on the port, an auto link behaves like a point-to-point link.
•
edge
—Configures the ports as edge ports.
•
point-to-point
—Configures the ports for an RSTP environment.
Backup Supports the designated port on the same attached LAN segment. Backup ports only exist when
the bridge is connected as a self-loop or to a shared-media segment.
Table 30: RSTP link types
Port Role Description
Auto Specifies the switch to automatically determine the port link type. An auto link behaves like a
point-to-point link if the link is in full duplex mode or if link aggregation is enabled on the port.
Otherwise, the link behaves like a broadcast link used for 802.1w configurations.
Edge Specifies a port that does not have a bridge attached. An edge port is placed and held in the STP
forwarding state unless a BPDU is received by the port.
Broadcast Specifies a port attached to a LAN segment with more than two bridges. A port with a broadcast
link type cannot participate in rapid reconfiguration. By default, all ports are broadcast links.
Point-to-point Specifies a port attached to a LAN segment with only two bridges. A port with port-to-port link type
can participate in rapid reconfiguration. Used for 802.1w configurations.
Table 29: RSTP port roles (continued)
Port Role Description