The paper describes a weakness in the pseudo random number generator (PRNG) in use by OpenBSD, Mac OS X, Mac OS X Server, Darwin, NetBSD, FreeBSD and DragonFlyBSD to produce random DNS transaction IDs (OpenBSD) and random IP fragmentation IDs.
You can download it from the following link: https://packetstormsecurity.com/files/download/63332/OpenBSD_DNS_Cache_Poisoning_and_Multiple_OS_Predictable_IP_ID_Vulnerability.pdf
Source: https://packetstormsecurity.com/files/63332/OpenBSD_DNS_Cache_Poisoning_and_Multiple_OS_Predictable_IP_ID_Vulnerability.pdf.html