External ip updates ??

First i wanna say i love sme server i was useing it for a long time ago but just got back to linux and everything is working fine and as it should but there is one thing i can´t find i will make a example i have 2 isp´s at home

Line a: 1mbit
Line b: 25mbit

and say i put line a in server i boot it and all works fine with line a ip adr dyndns even update all is good but say the line a is down or some other reason i wanna use line b then i take the cable out and plug it in and my problem is here the sme server don´t update the ip is there a timer haw often its updated or is there somehaw i can make the server update isp ip or do i have to reboot the server each time.

im running sme 7.0rc3

thanks for all the help i can get , kinda lost been to config files but mayby the wrongs ones and i really did look for over 5h now better go to sleep so late 05:00 cylon out.