* At a dialup modem pool in AT&T WorldNet, 58% of the TCP connections advertise ``SACK permitted" on the SYN packet, and 5% of the TCP connections advertise ``SACK permitted" on the SYN ACK. Thus, only 5% of the TCP connections actually use SACK. (From Anja Feldmann, trace from 12/99)
Web clients and servers:
* The TBIT tool reports on the fraction of web servers supporting SACK.
* At a single SACK+RFC1323 capable HTTP client, 15% of the TCP connections to over 115,000 IP addresses supported SACK. (From Richard Wendland at Netcraft, data from 3/00)
* 22.7% of the 70,000 web servers measured by the webstats project used SACK. (From Wes Eddy, trace from 8/00).
* From December 1998 to February 2000, the fraction of hosts sampled with SACK-capable TCP has increased from 8% to 40%. (From Mark Allman).
* The following stacks support SACK: Win98/2000, Linux, Solaris, IRIX, OpenBSD, AIX, and possibly BSDI, but SACK is not a given for high volume servers. (From Zachary Amsden, Richard Wendland, Venkat Venkatsubra)
* The first SACK implementation to ship in a commercial product was FTP Software OnNet 2.0 for Win95.
* For Solaris, SACK is used starting with Solaris 7. (From Kacheong Poon at SUN)