What is TCN in Spanning Tree?
When the switches receive this message they will reduce the aging time of the MAC address table from 300 seconds to 15 seconds (this is the forward delay timer). This message is called the TCN (Topology Change Notification).
Does RSTP have timers?
Rapid spanning doesn’t use timers to decide whether an interface can move to the forwarding state or not.
How does TCN work in RSTP?
This topic describes the process that RSTP uses to notify all bridges in the network of a TC. In 802.1D, any port state change generates a TCN. When an 802.1D bridge detects TC, it sends TCNs toward the root bridge. The root bridge sets the TC flag on the outbound BPDUs that are relayed to switches down from the root.
What are the timers involved in STP and RSTP?
Important Spanning Tree Protocol (STP) timers are hello timer, forward delay timer and max age timer and their default values are listed below.
- hello timer. The hello timer is the time interval between each Bridge Protocol Data Unit (BPDU) that is sent on a port.
- forward delay timer.
- max age timer.
What is difference between STP and RSTP?
Rapid Spanning Tree Protocol (RSTP) Rapid spanning tree protocol (RSTP) is as its name suggests, a faster transition to a port-forwarding state. Unlike STP, which has five switchport states, RSTP has only three: discarding, learning, and forwarding.
What is TCA BPDU?
BPDU. There are two types of BPDUs that are involved in the topology change mechanism in STP: Configuration BPDU: Root switch sends configuration BPDUs with set TC (topology change) and TCA (topology change acknowledgment) bit in flags field to notify all the switches about the topology change.
How do I change timer in spanning tree?
Procedure
- Enter system view.
- Set the forward delay timer. In STP/RSTP/MSTP mode: stp timer forward-delay time. In PVST mode:
- Set the hello timer. In STP/RSTP/MSTP mode: stp timer hello time. In PVST mode:
- Set the max age timer. In STP/RSTP/MSTP mode: stp timer max-age time. In PVST mode:
What is the convergence time for RSTP?
50 seconds
When default values are used for the maximum age (20 seconds) and forward delay (15 seconds), it takes 50 seconds for the device to converge. RSTP converges faster because it uses a handshake mechanism based on point-to-point links instead of the timer-based process used by STP.
Is TCN a BPDU?
TCN BPDUs are used to inform the upstream device and root bridge of topology changes. Configuration BPDUs with the TCA bit set to 1 are used by the upstream device to inform the downstream device that the topology changes are known and instruct the downstream device to stop sending TCN BPDUs.
What are timers in STP?
The most important timing parameters in STP calculation are forward delay, hello time, and max age. Forward delay is the delay time for port state transition. By default, the forward delay is 15 seconds.
What are the default timer used by STP?
STP Timers :
| Timer | Default Value |
|---|---|
| Hello | 2 seconds |
| MaxAge | 10*Hello time |
| Forward Delay | 15 seconds |
What is the main advantage of RSTP over SPT?
RSTP is an improvement over STP (Spanning Tree Protocol) mainly due to its reduction in convergence time – that is, the time it takes all switches on a network to reach a state of convergence, or agreement, on the topology of the network.