at a WR clock can have multiple ports in slave state, with each of them communicating with a different grandmaster clock-a form of "hot standby." This allows the WR clock to maintain the desired ac- curacy during an event that requires switching to a new grandmaster. Given the hardware support to assist in the time distribution, the actual PTP traffic is generally not as high in WR as one might expect. The number of Sync messages has a default of 1 per second with a possible range of 2 per second to 1 per 64 seconds. The domain number is fixed at 0. Gener- ally, the specification beyond that is mostly undefined (for example, transport type). WR is an open standard, for both hardware and software implementations, SO information and products supporting it are readily available. The current version as of writing is 2.0 from 2011. Compatibility with existing standards enables mixed networks, where time-critical end nodes are connected directly to a WR network core, while other less-critical devices use standard switches to connect to it. Note that the WR specification is likely to be replaced by the High Accuracy Delay Request-Re- sponse Default PTP Profile (Annex 1.5) from IEEE 1588-2019. 7.6 PTP Security It is clear that timing and synchronization is a critical component of our modern infrastructure, SO like all essential services, it will attract bad actors with malicious intentions, looking for any open vulnerabilities. Therefore, security of the timing distribution network is an important consideration for operators deploying it. From a security aspect, the timing distribution network has one advant- age when it comes to security and has a couple of other disadvantages that set it apart. The advantage is that the packet-based timing runs over essentially the same network as all the rest of the important data. This means that the normal security measures that network engineers perform for their data network now apply equally to the packet-based timing distribution network. It is bey- ond the scope of this book to