#### "The Linux Gazette...making Linux just a little more fun!"

# The Answer Guy

#### By James T. Dennis, linux-questions-only@ssc.com
Starshine Technical Services, http://www.starshine.org/

### TCP/IP SACK Support: When? Now!

From Alan Richard on Fri, 22 Jan 1999

Upon further investigation, I see that the 2.1.90 and later kernels have implemented RFCs 2018 and 1323. I found this on the http://www.psc.edu/networking/perf_tune.html page.

Thanks anyway, Alan

> Thanks for following up some quickly with the answer to your own question. I was going to have to hunt through kernel sources and the kernel mailing list if I was going to answer this one.

> To give you and idea of just how ugly that would be let me ask:

> > What is the TCP/IP SACK feature? What does it do?

> Why do we need/want it?

> It the Linux implementation any better or worse than others? (Or is it some feature where you pretty much either have it or you don't and there is no "better" or "worse")?

Alan Richard wrote:

> Hey AnswerGuy,

Do you know anyone with a good implementation of SACK for Linux? I'm running RedHat Linux 2.0.36. I've searched the web a bit under TCP, SACK, and RFC 2018, and have yet to find any patch available for download.

My officemate, Mark Allman, is the co-chair of the IETF TCP Implementation Working Group. He says that SACK and Large Windows (RFC 1323) are now the standard for TCP, with Windows98 and Sun 2.6 having them already implemented. Where is the Linux community with respect to implementing these? (Mark would like to know, too.)

Thanks

##### Copyright © 1999, James T. Dennis
Published in The Linux Gazette Issue 37 February 1999

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