DNS Instability

Hi all,

Every two weeks or so, I would be forced to switch back to my ISP’s DNS because Comodo DNS would suddenly fail to lookup yahoo, google (gmail, youtube etc), and hotmail.

I think this is an instability of the DNS and should be resolved to make it usable for most users. Even though I am familiar with these techie stuff, I still find it not too convenient to occasionally login to my router to change the DNS setting and then restart it.