АМАТЕК AN-SGM28P24-400 [114/322] Port role

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8.1.9 Port role

Fast convergence algorithm for MSTP using RSTP. This paper briefly introduces MSTP port

role and fast convergence in combination with RSTP。

RSTP provides fast convergence of specified port roles and decision activity topologies.

RSTP, based on IEEE802.1D STP, selects high priority switches as root switches. When RSTP

specifies a port role to a port：

Root port － When forwarding packets to the root switch switch provides the optimal path

cost。

Designated port － Connection specified switch。When forwarding packets from the LAN to

the root switch have the lowest cost path. Specifies that the port through which the switch

connects to the LAN is called a specified port。

Alternate port－ Provides a replacement path to the root switch of the current root por。

Backup port－Backup of a path that plays a specified port to the spanning tree leaf。A

Backup port exists only when the two ports are connected together in a point-to-point loop, or

when a switch has two or more connections to a shared LAN segment。

Disable port－There is no port role in the spanning tree operation。

Master port － On the shortest path of the domain root or the total root, it is the port

connecting the domain to the total root。

The root port or the specified port role is included in the active topology. The replacement

port or backup port role is not included in the active topology。

In a stable topology and fixed port role of the entire network, RSTP to ensure that every root

port and the designated port immediately moved to the forwarding state when all the replacement

port and backup port is always in the state of discarding. Port state control forwarding and learning

processing。

Fast convergence

In the following case, RSTP provides fast recovery: switch failure, port failure, or LAN fault,

which provides fast restoration for edge ports, new root ports, and connections to a point-to-point

connection：

Edge ports － If you configure a port as an edge port, the edge port is immediately migrated

to the forwarding state. You can open it as a boundary port only when this port is connected to a

single terminal or to determine the device that does not need to compute the spanning tree。