MTU setting

[chrisb691]

I'm connected to Optus cable, using a std Optus modem. I have a home network hung off the modem, using a Netgear WGR614 v4 wireless router.

2 PCs, and 2 printers, direct connect to the router, whilst the rest of the gear (2 pcs, 2 laptops) connect via wireless.

I haven't been the happiest with download speeds on my laptop, but put it down to the wireless connection. Because the router is upstairs, wireless connect speed can be all over the place. However, in the last couple of weeks, I've been trying to download some shopnotes pdf files, via Azureus, and it's been worse than dialup. Plus I've been getting a lot of bad data.

I've been monitoring my connection speeds using Speedtest.net (http://www.speedtest.net/), and over a period of a couple of months I have ranged from 400kbps - 770kbps.

On Monday night, I decided to have a closer look at the router settings, and eventually had a play with the MTU setting. Long story short, I ended up resetting the MTU from 1500 (default setting) to 1492.

Spectacular reults. Speedtest.net test now ranges between 1200kbps and 4500kbps. I'd had the laptop on continuously for a week, downloading the pdfs via Azureus, and was showing up to 10 days remaining. After changing the MTU, the whole lot came down in less than 3 hours. With a peak download rate of 524 Kb/s, and Azureus reports zero bad data.

I'm not an expert in MTU, in fact I find it to be all too complicated. However, if you have a similar setup to mine, and are connected to Optus, it may be worth a try. You can always change it back if it doesn't work for you. :)

EDIT: Just got this reading. http://www.speedtest.net/result/132888246.png (http://www.speedtest.net)

[q9]

The reason it works is because the MTU sizes should match or else you end up with a lot of dropped packets, which in turn results in a LOT of retransmissions. In fact there are cases where you need to set the MTU to be much smaller than normal but I don't think anyone is that interested.

Router firmware upgrades by our carrier would result in us losing all network communications as it would fudge the MTU settings, the result being our MTU sizes on our routers were different (larger) than their routers would allow, so the data packets would be dropped.

Basically, for speed, you want the largest MTU size that your carrier supports (which is typically 1492 for adsl) as it gives you the greatest percentage of data to protocol overhead.