[ubuntu] How long has my system IP address been assigned to it?

I have a wireless router that might have crash in the middle of the night since the system logs and dates have now reverted to 2004 and there's nothing before early this moing. While I have a system that was ruing all night and that is coected over wireless, is there a way to see how long it's coection has been up? Basically, I'm guessing that there's a way to see if it got assigned an IP address on my wireless network at a specific time.

I checked for the system's IP address in /var/log/syslog by word searching it with nano for "192.168.", but nothing came up.