Chapter 13. Benefits of TCP Timestamps

TCP Timestamps are an optional TCP header extension. By default, RHEL enables them and the kernel uses TCP Timestamps to better estimate the round trip time (RTT) in TCP connections. This results in more accurate TCP window and buffer calculations.

Additionally, TCP Timestamps provide an alternative method to determine the age and order of a segment, and protect against wrapped sequence numbers. TCP packet headers record the sequence number in a 32-bit field. On a 10 Gbps connection, the value of this field can wrap after 1.7 seconds. Without TCP Timestamps, the receiver could not determine whether a segment with a wrapped sequence number is a new segment or an old duplicate. With TCP Timestamps, however, the receiver can make the correct choice to receive or discard the segment. Therefore, enabling TCP Timestamps on systems with fast network interfaces is essential.

The net.ipv4.tcp_timestamps kernel parameter can have one of the following values:

By default, TCP Timestamps are enabled in Red Hat Enterprise Linux and use random offsets for each connection instead of only storing the current time:

# sysctl net.ipv4.tcp_timestamps
net.ipv4.tcp_timestamps = 1

If the net.ipv4.tcp_timestamps parameter has a different value than the default (1), revert the setting in the same way as you set it.