HP 1910 User Manual page 214

Port roles
A port can play different roles in different MSTIs. As shown in
Device B, Device C, and Device D. Port A1 and port A2 of Device A connect to the common root bridge.
Port B2 and Port B3 of Device B form a loop. Port C3 and Port C4 of Device C connect to other MST
regions. Port D3 of Device D directly connects to a host.
Figure 183 Port roles
MSTP calculation involves the following port roles:
• Root port—Forwards data for a non-root bridge to the root bridge. The root bridge does not have
any root port.
Designated port—Forwards data to the downstream network segment or device.
•
Alternate port—The backup port for a root port or master port. When the root port or master port
•
is blocked, the alternate port takes over.
Backup port—The backup port of a designated port. When the designated port is invalid, the
•
backup port becomes the new designated port. A loop occurs when two ports of the same
spanning tree device are interconnected, so the device blocks one of the ports. The blocked port
acts as the backup.
Edge port—An edge port does not connect to any network device or network segment, but directly
•
connects to a user host.
• Master port—A port on the shortest path from the local MST region to the common root bridge. The
master port is not always located on the regional root. It is a root port on the IST or CIST and still a
master port on the other MSTIs.
Boundary port—Connects an MST region to another MST region or to an STP/RSTP-running device.
•
In MSTP calculation, a boundary port's role on an MSTI is consistent with its role on the CIST. But
that is not true with master ports. A master port on MSTIs is a root port on the CIST.
Port states
In MSTP, a port can be in one of the following states:
Figure
201
183, an MST region has Device A,