dd-wrt settings 10:33 pm / 31 January 2009 by Tom, at Crooked Spoke
I’ve been struggling with some mild performance issues since flashing to dd-wrt. It has coincided with dealing with some dodgy wireless issues on my new Aspire One, so it’s been hard pinpointing which element is the weak link.
I’m going to stick with dd-wrt for now (I’m using a Linksys WRT54G rev8), and things are better since making a few changes this afternoon. I am running a straight 802.11g network. Some changes I made are as follows. I’m the first to admit that none of these settings are original to me - all of them came from suggestions found while searching.
- TX Power: I tried bumping up the TX power to 84mW as I had read suggested somewhere. But the unit started making funny noises during file transfers, and I didn’t find that overly endearing. On the suggestion of a professor of mine, I backed down the TX power. I’m doing fine now on 40-50mW. (Wireless -> Advanced Settings) For more on what I mean by “fine,” see below. Your mileage may vary depending on how much area you have to “paint” with wireless signal.
- Frame bursting: If you have only a few wireless clients (say 3 or less), frame bursting is supposed to help. (Wireless -> Advanced Settings)
- DTIM Interval: I turned down the DTIM interval (to 1). (Wireless -> Advanced Settings)
- ACK Timing: most performance tweak guides for DD-WRT suggest looking close at this one. Most I’ve seen suggest setting it to 0. I’m doing fine with 200 (default is 2000). (Wireless -> Basic Settings)
- Channel: This shouldn’t be a huge issue for non-enterprise users, but it can’t hurt to tweak a bit, right? Use the least congested channel; if at all possible, use channel 1, 6, or 11 as they are non-overlapping channels for the 2.4Ghz band. However, in most situations, it is preferable to use an overlapping channel if the non-overlapping channels (1, 6, and 11) are heavily used. If you live in a residential area - especially an apartment building or dormitory - these non-overlapping channels (especially 6, I would think) will be quite cramped. Avoid using channels with a lot of congestion. Use the Site Survey functionality on the “Advanced Settings” subtab of the Wireless tab and look for a channel that’s not being used.
- Mode: If you’re not using 802.11b at all, why run mixed mode at all? Switch to G-only if all your wireless devices are 802.11g capable.
- IP Filter settings: A big one that’s had big impact on my performance. Avoid setting the “Maximum ports setting” too high if you have a model with only 8MB of memory. Realistically, from what I read, don’t put the Maximum Ports Setting (Administration ->Management) above 2048 (even that’s pushing it). I also set the UDP and TCP timeouts to 120. These settings are especially important if you use torrents or similar peer to peer technologies that maintain a lot of half-open TCP connections (or embryonic TCP connections, depending on who you ask).
Notes on the signal strength on the status tab:
I have been experience intermittent signal dropping since using dd-wrt. It’s not necessarily severe enough that Windows realizes the connection has dropped, but it’s apparent from a lack of connectivity (Windows XP Home, the OS on my Aspire One, is poor enough with wireless that it apparently doesn’t realize when the connection has dropped). Reparing the connection has been remedying it, but of course I want to troubleshoot it. When torrenting, I was noticing dropping signal every 10 minutes or so - not acceptable, of course.
I had thought at first that the problem was poor signal quality. Though Windows reports “five bars” for my signal quality, I was concerned that the signal quality on the dd-wrt wireless status page for my clients was around 50% if not lower. After doing a bit of reading and thinking, this isn’t so alarming. Here’s why:
100% is the Land of Oz. You’ll never achieve “100% signal” (or near it) for the same reason you’ll never achieve the theoretical 54Mb/s throughput of 802.11g or the theoretical 11Mb/s of 802.11b: we live in the real world.
A bit of reading suggests that if there are no problems with signal dropping, don’t worry immensely about a 50% or so reading on the dd-wrt wireless status page. That’s a percentage of a theoretical signal quality that nobody will ever achieve (especially with “cheapy” home wireless access hardware).
A better number to look is the SNR (signal to noise ratio) - higher is better. I read on the dd-wrt forums that 40+ SNR is great.
So, my screenshot showing 53% quality and SNR of 41 is really nothing about which be concerned. In fact, based on what I read, it’s damn good. If you’re having performance issues, this may not be the place to be suspicious. Take a look at some of the settings mentioned above.