One potential explanation depending on your kernel version - traditional SYN cookies cannot encode TCP extensions, including window scaling, which will (nearly) always result in slower transfers. Newer kernels (The Googles aren&#x27;t giving me a kernel version, unfortunately) use the TCP timestamp option in addition to the sequence to encode a limited number of TCP options, including WS.<p>More info: <a href="http:&#x2F;&#x2F;www.inesc-id.pt&#x2F;pt&#x2F;indicadores&#x2F;Ficheiros&#x2F;165.pdf" rel="nofollow">http:&#x2F;&#x2F;www.inesc-id.pt&#x2F;pt&#x2F;indicadores&#x2F;Ficheiros&#x2F;165.pdf</a>