OCPBUGS-54148: Added PTP UDP OVNK primary interface note

Author: dfitzmau

Diff for: networking/ptp/about-ptp.adoc

@@ -8,6 +8,11 @@ toc::[]
 
 Precision Time Protocol (PTP) is used to synchronize clocks in a network. When used in conjunction with hardware support, PTP is capable of sub-microsecond accuracy, and is more accurate than Network Time Protocol (NTP).
 
+[IMPORTANT]
+====
+If your cluster uses the OVN-Kubernetes network plugin and PTP uses the User Datagram Protocol (UDP) for hardware time stamping, the hardware time stamping cannot be applied to primary interface devices, such as an Open vSwitch (OVS) bridge.
+====
+
 You can configure `linuxptp` services and use PTP-capable hardware in {product-title} cluster nodes.
 
 Use the {product-title} web console or OpenShift CLI (`oc`) to install PTP by deploying the PTP Operator. The PTP Operator creates and manages the `linuxptp` services and provides the following features: