Ubuntu Security Notice 661-1 – Version 2.6.27 of the Linux kernel changed the order of options in TCP headers. While this change was RFC-compliant, it was found that some old routers and consumer DSL modems would not route traffic for these systems when TCP timestamps were enabled. As a workaround, TCP timestamps were disabled via sysctl.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/71389/USN-661-1.txt
Source: https://packetstormsecurity.com/files/71389/Ubuntu-Security-Notice-661-1.html