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MTU Optimization

post #1 of 9
Thread Starter 
Hi,
I have a doubt about the MTU optimization process, following the procedure below.

I have to verify the parameters on my network equiments, any advice will be appreciated, I'm here for learn if possible:
ADSL WAN ROUTER - MTU 1444
NETGEAR R6220 ROUTER - MTU 1416
WINDOWS CLIENTS - MTU 1388
VPN SOFTWARE - MTU 1360



To find the correct MTU for your configuration you must run a simple DOS Ping test. You will simply send out ping requests and progressively lower your packet size until the packet no longer needs to be fragmented.

Please reference the following steps: The command for this ping test is ping www.overclock.net -f -l xxxx where "xxxx" is the MTU size that you are testing, you can use also any well known, pingable domain like ping www.google.com

Step 1 Open a DOS prompt screen by clicking on Start>Programs>MSDOS-PROMPT. You can also use the Run Command by clicking on Start>Run then type in "cmd"

Step 2 At the DOS Prompt type in ping www.overclock.net -f -l 1472 and hit Enter. Notice that the packet needs to be fragmented (packet needs to be fragmented but df set).

Step 3 Drop the test packet size down (10 or 12 bytes) and test again. Notice that the packet still needs to be fragmented.

Step 4 Drop the test packet size down more and test again until your reach a packet size that does not fragment. (reply from...).

Step 5 Once you have a test packet that is not fragmented increase your packet size in small increments and retest until you find the largest possible packet that doesn´t fragment.

Step 6 Take the maximum packet size from the ping test and add 28. You add 28 bytes because 20 bytes are reserved for the IP header and 8 bytes must be allocated for the ICMP Echo Request header. Remember: You must add 28 to your results from the ping test!

An example: 1440 Max packet size from Ping Test + 28 IP and ICMP headers 1468 is your optimal MTU Setting
post #2 of 9
You want to set the MTU to be the same on all your devices unless you are having trouble with packet loss between two devices. I would set the MTU to 1500 on all your devices, then start the optimization process from one of the windows clients, then when the optimal MTU is found, set all the devices to use the same value.

Having each device with its own MTU will just lead to confusion and all the devices effectively using the smallest MTU (which means more connection overhead).
post #3 of 9
Thread Starter 
Thanks @ShamrockMan, actually pinging from the ADSL Router, at 1444 size (not from the clients), looks ok.
I have to add 28 bytes also here? so the parameter that I have to set is 1472? or these 28 bytes are valid only in the ping procedure from clients? Probably I'm making confusion, but I want learn a little bit...


post #4 of 9
No. You don't have to change anything once you figure it out at the router.

An IP header only contains the sender and the final destination, so you only need to do the byte subtraction once, then set the MTU on everything to the same value.
post #5 of 9
Thread Starter 
Quote:
Originally Posted by ShamrockMan View Post

No. You don't have to change anything once you figure it out at the router.

An IP header only contains the sender and the final destination, so you only need to do the byte subtraction once, then set the MTU on everything to the same value.

thumb.gif setting up all the devices at 1444 everything looks ok... do you know the suite Auslogics Boost Speed? I found the Internet Optimization side pretty useful:

http://www.auslogics.com/en/software/boost-speed/


post #6 of 9
I'm not a fan of "Optimization" tools as they generally make things worse in subtle ways. They commonly increase speed of things by making them more unstable or by disabling power management features, increasing the cost of running your computer. They also like to claim they will defrag your hard-drive and a few other things, without mentioning they are just wrapping a bow around those features already built into windows (eg: they put a fancier looking UI in-front of them). The fact that all of these settings have trade-offs never seem to make it into any of these tools.

For things like the Internet, your performance typically cannot change much without modifying settings on the server you are connecting to (and sometimes all the routers between you and the server), so those parts are little more than snake-oil. MTU is one of them, since for any given connection, you are limited by the device with the smallest MTU, so you would have to get the entire rest of the Internet to agree with your MTU (unlikely). For talking to devices on the same network, adjusting MTU makes since, as it can greatly increase performance. The reason why things don't default to large MTUs is that it can make things slower over longer distances (typically not an issue for home or single office building scale use, only a campus/ISP level issue).
post #7 of 9
Thread Starter 
Quote:
Originally Posted by ShamrockMan View Post

I'm not a fan of "Optimization" tools as they generally make things worse in subtle ways. They commonly increase speed of things by making them more unstable or by disabling power management features, increasing the cost of running your computer. They also like to claim they will defrag your hard-drive and a few other things, without mentioning they are just wrapping a bow around those features already built into windows (eg: they put a fancier looking UI in-front of them). The fact that all of these settings have trade-offs never seem to make it into any of these tools.

For things like the Internet, your performance typically cannot change much without modifying settings on the server you are connecting to (and sometimes all the routers between you and the server), so those parts are little more than snake-oil. MTU is one of them, since for any given connection, you are limited by the device with the smallest MTU, so you would have to get the entire rest of the Internet to agree with your MTU (unlikely). For talking to devices on the same network, adjusting MTU makes since, as it can greatly increase performance. The reason why things don't default to large MTUs is that it can make things slower over longer distances (typically not an issue for home or single office building scale use, only a campus/ISP level issue).

I don't use Optimization Tools too, but in this case taking only the Internet Optimizer, I can set up the parameters of the network card easly. Probably with Windows 10 is automatic, I don't know if it's really useful. At least looks a detailed utility:



In terms of MTU, I'm just trying to understand how this parameter works between devices in the same work, like you said probably in a home network is not necessary modify it.
Between these configurations, in your idea which is the best one? you already answered me, please just give me a your opinion another time:

ADSL WAN ROUTER - MTU 1444
NETGEAR R6220 ROUTER - MTU 1444
WINDOWS CLIENTS - MTU 1444
VPN SOFTWARE - MTU 1444

ADSL WAN ROUTER - MTU 1444
NETGEAR R6220 ROUTER - MTU 1432
WINDOWS CLIENTS - MTU 1432
VPN SOFTWARE - MTU 1432

ADSL WAN ROUTER - MTU 1444
NETGEAR R6220 ROUTER - MTU 1432
WINDOWS CLIENTS - MTU 1420
VPN SOFTWARE - MTU 1408

In the last configuration, the risk of collisions is impossible right? what do you mean when you spoke about connection over head? also looking at Google...

Also finding the best parameter on my ADSL WAN ROUTER (the first device connected at the provider network), I'm doing the ping directly from the router console.
In this case, I have to add 28 bytes of IP and ICMP headers or there is something than a Windows client?


Thanks man
thumb.gif
Edited by Bride - 7/14/16 at 7:36pm
post #8 of 9
1444 is what you want for everything but the VPN. Measure the VPN software separately after setting everything else correctly as it would have an unknown amount of overhead (VPN runs on top of normal traffic).

The extra overhead comes from the application having to transmit a packet again because it got corrupted in transmission (or in the case of live streaming, a glitch as it doesn't have time to retransmit). If the MTU is too small, more of your bandwidth is used to transmit the IP header rather than the useful data.

Here is a good image to show you how the networking pieces are combined:



MTU basically controls how wide the IP data section is. There is only ever 1 IP header on the packet unless you are using a VPN. This is why you only need to subtract once. VPNs takes everything at the Internet layer and stuff it into the application layer, unpacks it at the other end of the VPN and sends it on its way. This reduces the size of the MTU if you are running traffic over a VPN. You can see this in the image that the Data square is much smaller than the Internet layer.
post #9 of 9
Thread Starter 
VPN at 1420 of MTU and all the devices at 1444. There is some software for verify the stability of your network, like the collissions?
Here a Speedtest pretty unuseful in this case...

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