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MTU Setting (again!)


MTU Setting (again!)


I know this has been discussed over and over, but my head is spinning after reading all the other posts on the topic! Shockedops:

What is THE definitive MTU setting, or is it just a case of finding one that works for you?

My current setting is 1454.

Community Veteran
Posts: 14,469
Registered: 30-07-2007

MTU Setting (again!)

Everyones connection and usage is different so you experiment with MTU and RWIN settings to achieve the best speed for individual connections.

The higher the MTU the more data you can get in a packet sent over the internet (to a max of 1500) but at the same time each connection between you and a website has an optimum setting which is the lowest configured of all the routers you go through between you and ther desitnation site. If you have an MTU that is too high for a specific network packets will be fragmented (split into multiple packets) which adds protocol overhead, reduces throughput and increases the likelyhood of packets being lost (which causes retransmissions).

The RWIN value determins how much data you can receive in packets before some form of achnowledgement is required for further data to be received. What value you use depends on the delays on indivudual connections and those delays increase the further away the site you are accessing is.

RWIN should always be a multiple of your MTU value.

Typical values for 512K ADSL are MTU: 1478 and RWIN: 17256. Lower values of RWIN may get faster speeds for local systems but slower speeds for remote systems like the USA, the same can apply to lower MTU values. Faster ADSL connections need corresponding higher RWIN values to make sure you utilise the extra speed effeciently.

Experiment and run several speed tests to come up with the best for you.

MTU Setting (again!)

what will i put for my 2mbit line then with these settings? i aint gettin over 200k Sad thanks
Posts: 235
Registered: 01-08-2007

MTU Setting (again!)

Hi alntim

For my 2 Mbps line I have set MTU to 1478 and RWIN to 63272. With these settings I get 1.92 Mbps which I think about the maximum for that line speed as measured on the Plus speed tester.

Whether this is accurate is another question, but this is the maximum result of playing around with the different settings in Dr TCP.

Regards, Mike