Hi, Martin Townsend wrote: > Hi, > > We have a closed network of embedded devices that we want to keep in > sync, the actual time is not important but the fact that they are all > on the same time is. One device is always the master so this is the > device that we want the others to synchronise to. > > Reading the documentation broadcast mode looks perfect. I'm currently > trying it out with the following configuration: > > # Broadcast Server > broadcast 192.168.2.255 > ttl 1 > > server 127.127.1.0 > fudge 127.127.1.0 stratum 14 > > ... > > # Broadcast Client > broadcastclient > > server 127.127.1.0 > fudge 127.127.1.0 stratum 14 > > ... > > > I've seen what look like valid messages being exchanged using tcpdump > but haven't seen any evidence that the times are converging but I > haven't really left it long enough. In the meantime I have read this > link > http://www.ntp.org/ntpfaq/NTP-s-config-adv.htm#AEN3658 > which seems to indicate that this setup is not possible. So my question is > Is broadcast mode with LCL a non started and if so what is the best > method for a private network that you need to keep in sync? > > I'm using the latest version 4.2.8p8, built using Yocto for an ARM cortex A8.
Broadcast mode requires some kind of authentication by default, so the client know the broadcast packet has really been sent by the trusted server. Without authentication any node on the network could start sending broadcast packets with a wrong time, and the clients might follow that wrong time. So you either have to configure authentication properly on the server *and* on each client, or you you have to disable authentication explicitly on each client. The question still remains why you think broadcast mode is better than normal client / server mode. in broadcast mode the client is unable to determine and compensate the packet delay on the network, so the resulting accuracy is worse than with client / server mode. Foe client / server mode you'd just need: on the server: server 127.127.1.0 fudge 127.127.1.0 stratum 0 on each non-Windows client: server aa.bb.cc.dd iburst on each Windows client: server aa.bb.cc.dd iburst minpoll 6 maxpoll 6 Of course you had to replace "aa.bb.cc.dd" by the real IP address of your server. "minpoll 6 maxpoll 6" avoid some limitations on Windows clients. The stratum of the local clock (127.127.1.0) on the server should be fudged to 0 so the server is visible as stratum 1. If you fudge the local clock to 14 then the server will be stratum 15, which is only one level above "not available". This is not accepted by some NTP implementations, and I'm not sure if ntpd as client would even accept a stratum 5 server, broadcast or not. Martin _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions