That is suspicious on 3333. How did you notice this? I'm going to cap a bit with Wireshark. Is your pool on 3333? I'm guessing it's not or you would not have mentioned this. It would be very unusual for DNS traffic on that port as mjk mentioned. It's probably nothing.
Just run netstat from the ssh console. It shows you all current connections. I have actually figured out it is related to the btcguild pool, if I drop packets going to the networkcentral range the btcguild pool starts showing up as dead. I can't really figure out how it is related, because none of the btcguild addresses I find seem to be anywhere near that range.