A couple of friends have some Actiontec GT701-wg DSL modems and I wanted to get their DSL modems flashed. The latest firmware (which was released in 2004) fixed a number of issues with those modems. These friends have simply gotten used to rebooting the modem fairly frequently to get their internet connection working properly. So I found some links to the firmware and some supplemental information:

• gt701-wg firmware from Qwest
• New firmware out for Actiontec GT701-WG

I really do think that ip is a big improvement from ifconfig, route, ifup, ifdown, and the other commands it replaces. Still I seem to have trouble remembering which commands you need to use the word “dev” and which ones you don’t and similar minor semantic issues (like parameter ordering). So I decided to try and compile a list of commands I commonly use to be used as a reference for studying.

I’ve seen this cause problems on both Xen and VMware though I suspect the problem is widespread. When a virtual ethernet device has checksumming enabled it can cause all sorts of network problems. I once got deep into debugging and found that with checksumming enabled packets larger than the MTU would be sent which would then cause a number of fragmentation messages to be sent. It was a mess, but easily correctable. Some specifics follow.

A number of years ago I tested the Linux ECN support and found that so much of the internet became inaccessible that keeping it turned off was the only sensible things to do. A few days ago while working on ingress traffic shaping I decided to try again. With ingress traffic shaping the only way to get a host to send slower is to drop packets forcing them to be re-transmitted. ECN could help alleviate waste by allowing a host to signal that packets are coming to fast without dropping packets that have already arrived. Unfortunately it did not take very long to learn that ECN is still unusable due to the large number of devices which will not pass traffic from ECN enabled hosts. My home DSL modem was one of them. Maybe someday ECN will work and enable smarter traffic control but I won't be holding my breath.

During some recent testing of traffic shaping I found that ingress traffic policing was important to maintaining low latency for high priority traffic such as VOIP. Unfortunately the traffic policy abilities of the Linux kernel are crude and limited to simply dropping packets over a given rate for specified conditions. This keeps latency low but requires the dropped packets to be retransmitted thus wasting bandwidth. IMQ has been one way of addressing it. Anyway I noticed that new IMQ patches were available for more recent Linux kernels and iptables versions. However, at the moment I’m more interested in trying the successor to IMQ, IFB (Intermediate Functional Block), which is supported in Ubuntu 7.10 (Gutsy Gibbon).

I was looking for information on some port numbers to see if any software used them and came across this link. I suspect it may come in handy in the future.

http://www.speedguide.net/ports.php