&gt; It doesn&#x27;t matter the MTU setting on your end for WAN and ISP &#x2F; interlink grade networks is meaningless [as] they don&#x27;t use Ethernet...<p>It absolutely <i>does</i> matter and is quite meaningful. :)<p>If you set your edge router&#x27;s Internet-facing MTU to 9k, and the upstream equipment&#x27;s MTU is smaller than that, then either your packets will be dropped, or PTMU Discovery will try to figure out the MTU of the path. (Better hope <i>everyone</i> along the path is correctly handling ICMP! :) )<p>&gt; The only time you would want to use large packets is pretty much when you can have a buffer...<p>Or if you have high-volumes of data to move and want to dramatically increase the data:Ethernet_frame_boilerplate ratio. :)<p>&gt; Also ... if you think about it the small packets are the most critical ones... [because they need to be dispatched as quickly as possible.]<p>Yes, but a larger MTU shouldn&#x27;t affect this. Set whatever socket options are required to get those packets on their way as soon as they&#x27;re created, and your system <i>shouldn&#x27;t</i> wait to fill an Ethernet frame before sending that packet.