10.5.9 NTP client and server support on the HMC Authentication support with a firewall Authentication support with a proxy HMC NTP broadband authentication support Note:  After joining the selected CTN, all systems within the current CTN are synchronized  with the Current Time Server of the selected CTN. A coupling link must be in place that  connects the CTS of the selected CTN and the CTS of the current CTN. During the transition state, most of the STP actions for the two affected CTNs are disabled.  After the merge is completed, STP actions are enabled again. For more information about planning and understanding STP server roles, see the following  publications: The NTP client support allows a STP-only CTN to use an NTP server as an ETS. This  capability addresses the following requirements: The NTP server becomes the single time source (the ETS) for STP and other servers that are  not IBM Z systems (such as AIXfi, and Microsoft Windows) that include NTP clients. The HMC can act as an NTP server. With this support, the z15 can receive the time from the  HMC without accessing a LAN other than the HMC and SE network. When the HMC is used  as an NTP server, it can be configured to receive the NTP source from the internet. For this  type of configuration, a LAN that is separate from the HMC/SE LAN can be used.  HMC NTP authentication can be used since HMC Driver 15 (zEC12/zBC12). The SE NTP  support is unchanged. To use this option on the SE, configure the HMC with this option as an  NTP server for the SE. Some client configurations use a proxy for external access outside the corporate data center.  NTP requests are User Datagram Protocol (UDP) socket packets and cannot pass through  the proxy. The proxy must be configured as an NTP server to get to target servers on the web.  Authentication can be set up on the client’s proxy to communicate with the target time  sources.  If you use a firewall, HMC NTP requests can pass through it. Use HMC authentication to  ensure untampered time stamps. GLYPH<SM590000> Server Time Protocol Planning Guide , SG24-7280 GLYPH<SM590000> Server Time Protocol Implementation Guide , SG24-7281 GLYPH<SM590000> Server Time Protocol Recovery Guide,  SG24-7380 GLYPH<SM590000> Clients who want time synchronization for the servers members of the STP-only CTN GLYPH<SM590000> Clients who use a common time reference across heterogeneous systems Chapter 10. Hardware Management Console and Support Element  443