I'm somewhat familiar with the general concepts of iptables, and would like to learn it in more detail. I'm hoping that my learning experience can also be useful.

The situation:

I'm running dd-wrt on my router. Despite its purported QoS skills, I'm still seeing connection latency shoot up hugely whenever there's an ongoing http connection, eg some large download. Under such conditions, it can take 10 seconds or more to load a basic webpage; sometimes the connections are dropped entirely. I've tried adjusting the parameters, dropping the allotted bandwidth for up and download to well under my limit, but nothing seems to work.

dd-wrt is configured to use HTB as the QoS algorithm; HFSC, although presented as an option, seems to cause the router to crash, and is rumoured to not actually work on any linux system.

I'd like to be able to troubleshoot this issue and hopefully improve the settings that dd-wrt is using, but I'm finding the learning curve a bit overwhelming. For starters I am not sure what HTB actually specifies: is this a set of iptables commands, or do some of those commands specify how HTB is to be used?

I would like it to prioritize based on protocol the way that it already supposed to, and in addition I'd like to have it drop the priority of connections which have a high total byte count, say over 400KB.

Also tips on utilities that can be run under dd-wrt to get more info on what's going on in there are appreciated. I've tried to get iftop to work but there were issues running curses. I'm leaning towards replacing dd-wrt with openwrt; comments on this strategy are also welcome. I suspect that I would be well advised to get a second router as a standin before trying that.

It may be worth noting that my total bandwidth is pretty limited (256Kbit/s).