Siemens RX1500 User Manual page 727

RUGGEDCOM ROX II
User Guide
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.
The learning state is entered when the port is preparing to play an active part in the network. The port learns
addresses in this state but does not participate in frame transfer. In a network of RSTP bridges, the time spent in
this state is usually quite short. RSTP bridges operating in STP compatibility mode will spend six to 40 seconds in
this state.
After learning, the bridge will place the port in the forwarding state. The port both learns addresses and
participates in frame transfer while in this state.
IMPORTANT!
Purely for purposes of management, ROX II introduces two more states: Disabled and Link Down. The
Disabled state refers to links for which RSTP has been disabled. The Link Down state refers to links for
which RSTP is enabled but are currently down.
Role
There are four RSTP port roles: Root, Designated, Alternate and Backup. If the bridge is not the root bridge, it
must have a single Root Port. The Root Port is the "best" (i.e. quickest) way to send traffic to the root bridge.
A port is marked as Designated if it is the best port to serve the LAN segment it is connected to. All bridges on
the same LAN segment listen to each other's messages and agree on which bridge is the Designated Bridge. The
ports of other bridges on the segment must become either Root, Alternate or Backup ports.
Figure 816: Bridge and Port Roles
1. Root Bridge 2. Designated Bridge
A port is alternate when it receives a better message from another bridge on the LAN segment it is connected to.
The message that an Alternate Port receives is better than the port itself would generate, but not good enough to
RSTP States and Roles
C
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1
2
2
5
D
3. Designated Port
3
1 2
3 3
1
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6
4. Root Port 5. Alternate Port
Setup and Configuration
1
4
2
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6. Backup Port
Chapter 5
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