zPET - IBM Z and z/OS Platform Evaluation and Test - Group home

Configuring PTP in the zPET Environment


The April 14, 2020 announcement for z15 T01 and z15 T02 introduced a new external time source option for Sysplex Time Protocol (STP) for an IBM Z Coordinated Timing Network (CTN), called Precision Timer Protocol (PTP), which is the subject of the IEEE 1588 standard.  PTP provides much better time accuracy for systems than was possible when using Network Time Protocol (NTP) alone as a time source.


Connectivity for PTP is managed via the IBM Z HMC/SE which will allow the use of a PTP-based external time source.  The goal is to enhance the role of IBM Z machines in a PTP environment that addresses the many governmental regulations and security concerns our clients are facing.


We configured our z15 server named T91.  Our testing included configuring our T91 machine to use PTP as External Timer Source (ETS) while in the Preferred Time Server (PTS) role as the Current Time Server (CTS). 


I’ll change T91’s ETS from NTP to PTP:

T91 is the PTS/CTS using NTP

Configure the External Time Source:

Change T91’s ETS from NTP to PTP

Successful connectivity to the PTP Server

Confirm the Configuration Change

Configuration change complete

T91 is the PTS/CTS using PTP

z/OS ‘D ETR’ command output with APAR OA59597 installed

Cannot get PTP to work on the z15 – the PTP Server signal is getting to the z15 SE, however the z15 SE cannot reach the PTP Server

Initial Experience changing T91’s ETS from NTP to PTP

The uniqueness of the zPET environment is both the NTP and PTP servers are on different subnets and both ethernet interfaces (em3 + em4) are being used where em3 is configured on the NTP server subnet and em4 is configured on the PTP subnet. Additional Network configuration is required on our z15 CPC such that it was able to get a signal from the PTP server.

Any z15 CPC that has these characteristics will require actions to get  PTP signals (details along with screen captures below):

  • The PTP server(s) and their ip address(es) the SE is connected to need to be known.
  • The SE’s route table needs to be updated thru the SE panels (static route needs to be added thru Customize network Settings, which will allow the route to persist across SE reboots).

The first time PTP was configured on T91 – Connection Failure

The em3 interface on the SE to the PTP server fails

Both the em3 and em4 interfaces to the PTP server fail

The PTP Grandmaster ID appearing in the above panel indicates the PTP signal can reach T91’s SE


T91 needs to talk to the PTP server, however the default route goes over the em3 interface:

  • The em3 interface is on a different subnet than the PTP server
  • The em4 interface has been configured with a subnet for the PTP server, so the T91 SE need to have it’s network routing table updated such that it could communicate with the PTP server, which is an action all z15 clients need to take to use PTP in a similar configuration – The ip address of the PTP server needs to be known and the network routing on the SE needs to be updated (see steps below)


Update T91’s Network Routing Table:

  • SE Management --> Customize Network Settings

Routing tab --> New

Select Net for static route

  • Provide:
    • Route Type: Net (for subnet route)
    • Destination: <ptp.ip.subnet.address> of the form nn.nn.nn.0
    • Gateway: <gateway.of.ptp.server>
    • Subnet mask:
    • Adapter: em4
    • Then select OK


OK to add

Panel will show:
  • Destination: <PTP server subnet> of the nn.nn.nn.0 format
  • Gateway: <PTP server gateway>
  • Subnet Mask: 255.255.0

Yes, to initiate SE reboot:

Network settings updated (Automatic reboot of SE will commence)

T91’s network routing table has been updated and it can successfully connect to the PTP Server and the ETS can be changed

Back to configuring the External Time source to use PTP, Verify PTP Interfaces is now successful for em4

Select close and proceed with the configuration and successfully performed in the beginning of this blog

You’re now on your way to configuring PTP as the ETS on your z15 server using the em4 interface where the PTP server is on a separate subnet