TCP Timestamp values, as specified in RFC 1323, are intended to improve the performance of TCP by increasing the accuracy of RTT measurement, especially in the case of lost packets, and allow systems to determine if a wrapped sequence number is the result of an old packet or a new connection. So TCP timestamps are used to provide protection against wrapped sequence numbers.
But it is possible to calculate system uptime and boot time while TCP timestamps is enable. These calculated uptimes and boot times can help in detecting hidden network-enabled operating systems see TrueCrypt, linking spoofed IP and MAC addresses together, linking IP addresses with Ad-Hoc wireless APs, etc.
E.g. By using the security scanning tools like Nmap. It is possible to know how long a system has been up also allow to determine whether security patches that require re-boot has been applied or not.
To Disable Timestamp in SonicwALL steps are as follows:
1. Login to the management interface in SonicWall through a browser.