why always the clock of RB1100ahx2 has to be set every time when the router rebooted ???
it gives always Jan/01/1970

because routerboard do not have batteries
when you reboot theclock is set to 0
you need to configure ntp client if you want to automatically setup the clock

how i can get ntp clients can you give me more expression ?

I use winbox but cli would work too.
first click on system on left and chose clock. set your time zone. don't worry about date or time.
then click on system and ntp or sntp. now click on enable then unicast. the address boxes will open up and you can put in you NTP server ip address or a ntp site on the internet. google to find ones close to you. I use 192.43.244.18 and129.6.15.29. click on apply and your routher board should not contact the NTP server and get the correct time. you can click on log on the left and see if it changed the time. This will automatically connect each time you reboot and get new time.

I hope this help you.

It depends on whether you have ntp package installed or not, you can check it in /system packages.
If it is installed you can configure ntp client, if not you can configure sntp client, which is practically the same.
Now to configure ntp client go to System ntp client, there select enabled, mode=unicast, primary server=europe.pool.ntp.org
and secondary server=time.nist.gov

@gcs we posted at the same time

gcs & Caci99 thanx alot for ur help