RuggedCom RS400 manual Rstp States and Roles

Spanning Tree

•RSTP offers edge port recognition, allowing ports at the edge of the network to forward frames immediately after activation while at the same time protecting them against loops.

While providing much better performance than STP, IEEE 802.1w RSTP still required up to several seconds to restore network connectivity when a topology change occurred.

A revised and highly optimized RSTP version was defined in the IEEE standard 802.1D-2004 edition. IEEE 802.1D-2004 RSTP reduces network recovery times to just milliseconds and optimizes RSTP operation for various scenarios.

ROSTM supports IEEE 802.1D-2004 RSTP.

5.1.1 RSTP States and Roles

RSTP bridges have roles to play, either root or designated. One bridge, the root bridge, is the logical center of the network. All other bridges in the network are designated bridges.

RSTP also assigns each port of the bridge a state and a role. The RSTP state describes what is happening at the port in relation to address learning and frame forwarding. The RSTP role basically describes whether the port is facing the center or the edges of the network and whether it can currently be used.

State

There are three RSTP states: Discarding, Learning and Forwarding.

The discarding state is entered when the port is first put into service. The port does not learn addresses in this state and does not participate in frame transfer. The port looks for RSTP traffic in order to determine its role in the network. When it is determined that the port will play an active part in the network, the state will change to learning.

Forwarding

Forwarding Timer Expires

Or Active RSTP Handshake has

Occurred

Learning

BPDUS indicate port should not be active

Forwarding Timer Expires Or Active RSTP Handshake

	Discarding
RSTP Disabled in any state	Link rises or falls
Disabled	Link Down
	RSTP Enabled

Figure 94: Bridge and Port States

ROS™ v3.5 134 RS400