VPN

This is my configuration

Network A ---- Monowall A ----- Internet ----- Router B ---- Monowall B ---- Network B

Network A and B are connected with a IPSec VPN.
Monowall A and Router B got a Dynamic DNS name.

The problem appear if the connection between Internet and router B fails.
When it comes back the IPSec will not reconnect automatically. I have to restart the monowall B.
I guess that this is related to that Router B will get a new IP-address when connection gets back.
And that Monowall B don't get this information without restarting.

Does someone know how I can solve this problem?

Ok. Found that there is an option saying IPsec DNS check interval in the "advanced" page. I use the default value, 60 seconds. This can't bee the problem then...
Any suggestions?