On 06/11/06, Dotan Cohen <<a href="mailto:dotancohen@gmail.com">dotancohen@gmail.com</a>> wrote:<div><div> </div> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> > I would ask your ISP why they have their kit running on 1400 MTU and thus > you having to mess around with your settings though. Seems a little odd in > this day and age. If you find this unusual, then I will ask them. Want to tell me what it should be set to, and the disadvantages and advantages of each setting? I want to be well armed when I ask them, not just some ignorant Parrot repeating what I've been told. Educate me a bit. </blockquote> </div> OK, the MTU is the Maximum Transmission Unit. It's a preset number of bytes and effectively determine the largest packet which will be sent. Any packets which are greater than 1500 bytes will be fragmented, or split into 2 smaller packets. The standard MTU for Internet transmission (unless you're on specialised hardware) is 1500 bytes. 8 bytes are normally reserved for packet overhead. So, your router will pass through packets of up to 1500 bytes, and your NIC will normally pass through packets of the same size. The only time you should have to change this is when some other device down the line cannot handle a 1500 byte packet which, if your ISP is requesting you send smaller packets, it sounds like you have. From the numbers you've quoted they want you to use an MTU of 1392, which implies something upstream from you can only handle 1400 byte packets (1392 + 8bytes of packet red-tape). If you start sending packets of this size, then that device will be ahppy but obviously your throughput is hampered as you have to sent more packets to transfer the same amount of data, thus "cramping" your throughput. If you stick to sending 1500 byte packets, the rogue device will have to do extra work to split the packets on your behalf. If you drop down to 1392, as requested, your slightly impact your throughput, but the rogue device has less work to do. If they had requested a 1492 byte MTU it would be FAR more believable but 1392, to my limited knowledge, is an odd size. I would just double-check it and confirm that someone hasn't made a typo! -- Steve Despair - It's always darkest just before it goes pitch black...