User guide

Rapid Spanning Tree Protocol
ExtremeWare 7.2e Installation and User Guide 199
RSTP Terms
Table 33 describes the terms associated with RSTP.
RSTP Concepts
This section describes important RSTP concepts.
Port Roles
RSTP uses information from BPDUs to assign port roles for each LAN segment. Port roles are not
user-configurable. Port role assignments are determined based on the following criteria:
• A unique bridge identifier (MAC address) associated with each bridge
• The path cost associated with each bridge port
• A port identifier associated with each bridge port
Table 33: RSTP Terms
Term Description
root port Provides the shortest path to the root bridge. All bridges except the root bridge,
contain one root port. For more information about the root port, see “Port Roles” on
page 199.
designated port Provides the shortest path connection to the root bridge for the attached LAN
segment. There is only one designated port on each LAN segment. For more
information about the designated port, see “Port Roles” on page 199.
alternate port Supplies an alternate path to the root bridge and the root port. For more information
about the alternate port, see “Port Roles” on page 199.
backup port 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. For
more information about the backup port, see “Port Roles” on page 199.
edge ports Ports that connect to non-STP devices such as routers, endstations, and other hosts.
Edge ports are not part of the RSTP configuration.
root bridge The bridge with the best bridge identifier selected to be the root bridge. There is only
one root bridge in the network. The root bridge is the only bridge in the network that
does not have a root port.