Cisco Systems PTP white paper (June 2020)

PTP best practices

Following are some of recommended best practices when using PTP:

●     Configure the switch to work in boundary-clock mode when supported

●     Ensure the number of slaves connected to a switch does not exceed the verified scalability.

●     Configure the PTP-slave devices to operate in slave-only mode

●     Ensure certified optics and transceivers are used and the mean path delay is low, and most importantly, not varying too much

Spine & Leaf topology


PTP deployment example in non-redundant networks

PTP deployment example in redundant network utilizing redundant PTP feeder switch



PTP and multi-site deployments

In a multi-site deployment, sometimes there is a requirement to extend PTP across sites. If these sites are geographically in the same location, connected over a direct fiber, PTP can be extended (Figure 9). When fabrics are in different geographical locations connected over Wide Area Networks (WAN), care must be taken when extending PTP. Varying latency across a WAN can compromise PTP accuracy as the PTP mean path delay is constantly changing. At times, it is recommended to use different PTP grandmasters in each site and not extend PTP across these sites



Troubleshooting PTP on Cisco NX-OS

# show ptp corrections

  • Displays PTP timing info.The corrections should be under 500 ns, and the mean path delay should be around the same value and not changing constantly.

# show ptp brief

  • Displays the which ports on the switch are in SLAVE mode and receiving PTP from a GM

  • Displays the which ports on the switch are in Master mode and sending PTP to endpoint devices

# show ptp parent

  • Displays details of the GM being used on the system (IP address, mac address, domain, class , priority )

# show ptp clock

  • Displays details of the PTP clock being used by the switch (IP address, mac address, domain, class , priority )


Cisco Nexus switches that support PTP media profiles (dated June 2020)

Following is a list of Cisco switches that support the PTP media profiles:

●     Cisco Nexus 9200 Series Switches

●     Nexus 9300-EX Switch

●     Nexus 9300-FX Switch

●     Nexus 9300-FX2 Switch

●     Nexus 9364C

●     Nexus 9508-R with N9K-X9636C-R, N9K-X9636Q-R, N9K-X9636C-RX

●     Nexus 9504-R with N9K-X9636C-R, N9K-X9636Q-R, N9K-X9636C-RX