This document specifies an algorithm for the generation of TCP Initial Sequence Numbers (ISNs), such that the chances of an off-path attacker guessing the sequence numbers in use by a target connection are reduced. This document revises (and formally obsoletes) RFC 1948, and takes the ISN generation algorithm originally proposed in that document to Standards Track, formally updating RFC 793.
You can download it from the following link: https://packetstormsecurity.com/files/download/109408/rfc6528.txt
Source: https://packetstormsecurity.com/files/109408/RFC6528-Defending-Against-Sequence-Number-Attacks.html