While it has been confirmed that Nexus 3K, 5K, and 7K hardware "support" only the 2-step PTP sync method, there are two serious problems with the code as it stands.
First, NX-OS fails to ignore the unsupported 1-step method and erroneously accepts and processes 1-step messages leading to a failure of the process to converge to the correct time. If Nexus will not support 1-step, then it must at least IGNORE 1-step.
Secondly, and I feel more importantly, it is not Cisco's choice whether or not to "support" the 1-step sync method. It is a requirement that ALL devices that support the IEEE1588 specification must defer to the master clock's sync method selection. If the Master clock has chosen the 1-step method, then the slave clock must use it. A failure to do so is a violation of the IEEE1588 specification.
In order for NX-OS to be considered IEEE1588 compliant, it must accept the 1-Step sync method when such is chosen by the master clock.
From the IEEE1588 v2, Clause 11: "Clock offset, path delay, residence time, and asymmetry corrections":
The <offsetFromMaster> value shall be computed by the slave as follows:
a) Upon receipt of a Sync message the slave shall generate a timestamp
<syncEventIngressTimestamp> corrected for latency per 7.3.4. If the delayAsymmetry, see
7.4.2, of the path connected to the ingress port is known, the corrections of 11.6 shall be made.
b) If the twoStepFlag bit of the flagField of the of the Sync message, is FALSE, indicating that a
Follow_Up message will not be received, then the
<offsetFromMaster> = <syncEventIngressTimestamp>
<originTimestamp>
<meanPathDelay> correctionField of Sync message.
