Cisco Bug: CSCvi67983 - Spikes in PTP mean path delay value can be observed intermittently
May 15, 2018
- Cisco Nexus 3000 Series Switches
Known Affected Releases
Symptom: Periodically Mean path delay value reported as very high (around 0.5 sec) on slave PTP switch `show system internal ptp info calculations` ... 134) Event:(null), length:8, at 276528 usecs after Fri Feb 2 00:05:38 2018 131) Event:(null), length:8, at 547939 usecs after Fri Feb 2 00:05:40 2018 Mean path delay 54 132) Event:(null), length:48, at 76923 usecs after Fri Feb 2 00:05:40 2018 slave_if 1a000000, master_ts 1517529977 s 37155840 ns,slave_ts 1517529977 s 37155943 ns, ts_err 0 -50 133) Event:(null), length:8, at 788014 usecs after Fri Feb 2 00:05:39 2018 Mean path delay 53 134) Event:(null), length:8, at 276528 usecs after Fri Feb 2 00:05:38 2018 Mean path delay 505001966 135) Event:(null), length:48, at 3693 usecs after Fri Feb 2 00:05:37 2018 slave_if 1a000000, master_ts 1517529973 s 997105950 ns,slave_ts 1517529973 s 997105980 ns, ts_err 0 22 It results in high offset from master in "show ptp clock" - until next mean path delay calculation. Conditions: Issue was observed on PTP Slave device in the following scenario, N3500 (PTP slave) === N3500 (PTP master) === GMC This issue was observed when workload on CPU of Master PTP switch is high (heavy SNMP polling, e.t.c). On this scenario some of PTP followup packets can be missed. Miss of followup packets itself is not a problem (it just causes PTP correction will not occur when PTP followup is missed). In some conditions when followup packets are missed (exact condition not known yet) it causes PTP slave to take incorrect t1/t2 values for mean path delay calculation, e.g. takes t1 and t2 from packets with not-matching sequence ID.
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