Netgear XCM8806 Chassis User Manual - Page 549

NETGEAR 8800 User Manual In XCM8800, STP edge safeguard disables a port when a remote loop is detected. A remote loop causes BPDUs to be exponentially duplicated which caused high CPU utilization on the switch even though the port was transitioned to a blocked state. RSTP Timers For RSTP to rapidly recover network connectivity, RSTP requires timer expiration. RSTP derives many of the timer values from the existing configured STP timers to meet its rapid recovery requirements rather than relying on additional timer configurations. Table 54 describes the user-configurable timers, and Table 55 describes the timers that are derived from other timers and not user-configurable. Table 54. User-Configurable Timers Timer Hello Forward delay Description The root bridge uses the hello timer to send out configuration BPDUs through all of its forwarding ports at a predetermined, regular time interval. The default value is 2 seconds. The range is 1 to 10 seconds. A port moving from the blocking state to the forwarding state uses the forward delay timer to transition through the listening and learning states. In RSTP, this timer complements the rapid configuration behavior. If none of the rapid rules are in effect, the port uses legacy STP rules to move to the forwarding state. The default is 15 seconds. The range is 4 to 30 seconds. Table 55. Derived Timers Timer TCN Topology change Message age Hold Description The root port uses the topology change notification (TCN) timer when it detects a change in the network topology. The TCN timer stops when the topology change timer expires or upon receipt of a topology change acknowledgement. The default value is the same as the value for the bridge hello timer. The topology change timer determines the total time it takes the forwarding ports to send configuration BPDUs. The default value for the topology change timer depends upon the mode of the port: • 802.1D mode-The sum of the forward delay timer value (default value is 15 seconds; range of 4 to 30 seconds) and the maximum age timer value (default value is 20 seconds; range of 6 to 40 seconds). • 802.1w mode-Double the hello timer value (default value is 4 seconds). A port uses the message age timer to time out receiving BPDUs. When a port receives a superior or equal BPDU, the timer restarts. When the timer expires, the port becomes a designated port and a configuration update occurs. If the bridge operates in 1w mode and receives an inferior BPDU, the timer expires early. The default value is the same as the STPD bridge max age parameter. A port uses the hold timer to restrict the rate that successive BPDUs can be sent. The default value is the same as the value for the bridge hello timer. Chapter 18. STP | 549