Riverstone Networks WICT1-12 - Manual (Page 75)

Riverstone Networks RS Switch Router User Guide Release 8.0 5-11
Bridging Configuration Guide Configuring a Port- or Protocol-Based VLAN
5.6.3 STP Dampening
STP creates a loop free, active topology in a network by placing ports in a forwarding or blocking state. When a port
moves to the forwarding state, it transitions from listening, to learning, and then to forwarding. Whenever this
transition happens, there is a chance that some traffic may be lost. If this port state transition happens rarely, the traffic
loss is insignificant. On the other hand, if this happens frequently, it can adversely affect the network. STP dampening
addresses this issue.
When a root port stops receiving BPDUs from the root bridge, a new root port is selected. If the original root port starts
receiving BPDUs from the root bridge once again and STP dampening is enabled on the port, traffic is not immediately
switched back to it. Instead, the port is monitored until it satisfes a stability condition, which is that it receives a certain
number of STP configuration BPDUs during a specified period of time. If the port satisfies this condition, then it is
considered stable and traffic is switched back to it. Otherwise, it remains in an unstable state and is continuously
monitored until it satisfies the stability condition. This feature ensures that ports are stable before they move to a
forwarding state and traffic is switched back to them.
Note that dampening will not occur if the port on which STP dampening is enabled goes down and comes up again.
Instead, traditional STP configuration occurs.
To enable STP dampening on a port, enter the following command in Configure mode:
Note STP dampening cannot be used in conjunction with RSTP.
The RS has defaults for the period of time a port will be monitored (10 seconds) and the number of BPDUs that need
to be received (10) during this period. You can change these defaults by entering the following command in Configure
mode:
5.7 CONFIGURING A PORT- OR PROTOCOL-BASED
VLAN
To create a port or protocol based VLAN, perform the following steps in the Configure mode.
1. Create a port or protocol based VLAN.
2. Add physical ports to a VLAN.
Enable STP dampening on a port.
stp set port
<port-list>
dampening enable
Set parameters for STP dampening.
stp set bridging damp-monitor-time
<seconds>
damp-bpdu-count
<number>