This was particularly noticeable when streaming video: the video would have to be reloaded each time the lease expired.
This article gave a fix which worked:
http://yllus.com/2011/03/25/fix-my-dd-w ... dhcp-lease
What I did was:
Add a rule to specifically allow those (DHCP renewal) messages. Do this by navigating within your router’s interface to Administration > Commands, and entering the following into the Commands fields:
iptables -I INPUT 2 -p udp --sport 67 --dport 68 -j ACCEPT
Finally, press the Save Firewall button to save the rule to be executed whenever the router is restarted.