This article explains the reason for 'RTT exceeded threshold' message on MX broadband network gateway (BNG), and introduces the feature of RTT Load Throttle of resource-monitor.
Example 'RTT exceeded threshold' message:
Jan 6 02:09:27 2020 MX-BNG bbesmgd[18216]: %DAEMON-4-SMD_RSMON_RTT_EXCEEDED: RTT exceeded threshold for FPC 3, throttle_phase_count 1
Jan 6 02:09:30 2020 MX-BNG bbesmgd[18216]: %DAEMON-4-SMD_RSMON_RTT_NOMINAL: RTT returned below threshold for FPC 3
Jan 6 12:27:36 2020 MX-BNG bbesmgd[18216]: %DAEMON-4-SMD_RSMON_RTT_EXCEEDED: RTT exceeded threshold for FPC 3, throttle_phase_count 2
Jan 6 12:28:18 2020 MX-BNG bbesmgd[18216]: %DAEMON-4-SMD_RSMON_RTT_NOMINAL: RTT returned below threshold for FPC 3
When this message is seen, the subscriber login may be failed.
With RTT Load Throttle feature enabled, when PFE becomes too busy, RSMON RTT Load Throttle feature kicks in and deny the new subscriber login; on subscriber login retry and PFE CPU in normal level, login will succeed. Without this feature, the subscriber would have gone to active state but no traffic will be flowing for a period of time.
Use the command below to check if RTT Load Throttle feature has been enabled:
user@MX-BNG> show system resource-monitor summary
Resource Usage Summary
Throttle : Enabled
Load Throttle : Enabled <-- indicates RTT Load Throttle has been enabled
Heap Mem Threshold : 70 %
IFL Counter Threshold : 95 %
Round Trip Delay Threshold(ms) : 1000 <-- RTT Throttle value
Filter Counter Threshold : 100 %
Expansion Threshold : 95 %
CoS Queue Threshold : 100 %
MFS threshold : 70 % Used : 0
Slot # 0
Client allowed : Yes
Service allowed : Yes
Heap memory used : 339204848 In % : 18
Average Round-trip Delay(ms) : 103 (30 ) Round-trip Delay(ms) : 103 <-- RTT Delay, the 30 in bracket means that the average is taken for last 30 secs
MAX session rate allowed(%) : 100
Client denied : 1524 <-- the counter of new subscribers have been denied
Service Denied : 0
Performance Denial Client : 1524 <--
Performance Denial Service : 0
IFL Denied : 0
Filter counter memory IFL counter memory Expansion memory
PFE # used | % used | % used | %
0 17848880 44 304096 0 0 0
1 17754480 44 274832 0 0 0
CoS Queue Utilization
PFE # Scheduler Block # Used %
0 0 88 0
0 1 88 0
1 0 24 0
1 1 24 0
If 'Average Round-trip Delay' is 'exceeded Round Trip Delay Threshold', the 'RSMON RTT Load Throttle' is triggered and system reports the log message.
There is a hidden command to adjust RTT Threshold value. Setting it to a large value can decrease the frequency of logging.
user@MX-BNG# set system services resource-monitor rtt-parameters rt-delay-threshold <value-in-millisecs>
If you prefer to disable this feature, use command below:
user@MX-BNG# set system services resource-monitor no-load-throttle