XBOX 360 and MTU (plus others)

Hi all,

Recently I upgraded my internet connection (30mbs to 60mbs), and Steam - for some reason, was not doing that great at using this improved download limit.

So after doing a fair bit or research I found there are a few things that you can do to boost your download speed. One of which was manually setting your MTU (so file chucks are sent to you at the maximum speed your network can handle, insuring partial chunks are not sent seperately, hogging your bandwidth).

So I did this, and found that the maximum speed that my router and network can handle is 1272 bytes per package (+28 for header rounds this to 1300) which is what I set my MTU to.

This had a marked improvement to my download speed from Steam, jumping from 3Mb/s to 5.8Mb/s - it also dropped my ping in FPS games (Planetside 2) and also COD BO 2 on the PS3. - this made gaming waay better.

Annoyingly, I then booted up the Xbox, and the bloody thing complains that MTU is set too low and I can't connect to XBL on that. After a quick google it turns out that the XBox 360 requires a MTU set to a minumum of 1364 bytes.

This I can't understand. I have tested my network and XBL was working with it *set* to 1500 (default) even though this amount of data could not pass through the fibre, but when I set it correctly it no longer works.

So my questions are twofold.

Is my PC lying to me when its telling me the maximum MTU available?
Is there some way to con the bloody xBox into thinking that the MTU is ok for it?

I would rather not change the MTU up, and deal with the fragmenting cos my download speeds and ping are significantly better.

4 answers Last reply
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  1. It is unlikely you are being limited to a mtu of 1300. Almost everything uses 1500. If you have a PPPoE type connection then there is another set of headers but it is still well over 1400.

    It pretty easy to find the maximum fragment size. Set you pc back to default. Then use the ping command to send pings to your router and your ISP router with various length packets. You ping with the do not fragment flag set and see how large a packet you can pass.
  2. hi john,

    from what I could tell 1500 was the maximum that any network can use, but real world situations dont achieve this.

    as to if pppoe or pppoa; buggered if i know, its virgin fibre, so all on their box.

    as to your suggestion to ping packets, that is how I identified the correct mtu in the first place, hence the +28 for headers. - this resulted in 1300 with the set default MTU of 1500.
  3. I wonder what they are doing that is causing the MTU to be so low. Even when I have run things over IPSEC VPN tunnels I have not had to set it that low.

    What happens if you leave the router at the default but set your PC MTU lower and leave the xbox to suffer with the fragments...which I better than not working at all.

    Its been a while but I think you reset the MTU with the NETSH command.
  4. If I leave the MTU set to 1500 everything works, but seeing as adjusting the mtu affects my ping drastically from approx 45 ms (with random spikes all the way up to 900ms) down to 14 ms (with no spikes, ever) - all whilst pinging google - I feel as if I am between a rock and a hard place.
    Streaming video streams more consistently and the improvement to online gaming is staggering, but the xbox doesn't work, but if I set the mtu to default the xbox works but everything else is crap.

    To be honest, if I don't find an answer soon I might just get rid of the xbox.
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