8 messages in org.freebsd.freebsd-ispRe: Enable SACK | From | Sent On | Attachments |
|---|---|---|
| Joao Pagaime | Jul 12, 2000 6:51 am | |
| Dan Nelson | Jul 12, 2000 7:19 am | |
| Luigi Rizzo | Jul 12, 2000 7:22 am | |
| Joao Pagaime | Jul 12, 2000 9:31 am | |
| Jonathan Lemon | Jul 12, 2000 9:52 am | |
| James Wyatt | Jul 12, 2000 10:00 am | |
| Kevin Oberman | Jul 12, 2000 10:50 am | |
| Paul Saab | Jul 12, 2000 2:21 pm |
| Subject: | Re: Enable SACK | |
|---|---|---|
| From: | Kevin Oberman (ober...@es.net) | |
| Date: | Jul 12, 2000 10:50:05 am | |
| List: | org.freebsd.freebsd-isp | |
Date: Wed, 12 Jul 2000 12:01:11 -0500 (CDT) From: James Wyatt <jwy...@rwsystems.net> Sender: owne...@FreeBSD.ORG
Ok, I'll bite. It won't be the first time I'va asked a question and learned something from this group of folks... Feel free to answer in private email or post to the list(s).
What is SACK and what is good/bad about it? I don't intend to start a flame war, but really would like to know. I think I can go read RFC1323 and get the gist of it this afternoon... TIA - Jy@
SACK is a TCP enhancement to prevent a common problems of connections oscillating in speed between line rate and near zero when several packets are lost in a single transmission window. It is NOT part of RFC1323 which covers a number of other enhancements in TCP to enhance performance over very high speed links. It is covered in RFC2018, "TCP Selective Acknowledgment Options", and is a standards track RFC.
I'm quite surprised to hear that FreeBSD does not support it as this is a serious problem on large latency links at OC-3 and above. It's a really big issue at higher speeds. When we did "fat pipe" testing over an OC-12 from Berkeley, CA to Chicago, IL, we had to enable SACK along with the 1323 stuff on the Suns that were used in the test to get over 300 Mbps on a single TCP stream. I hate to think that Sun does TCP better than FreeBSD. (Compaq, IBM, and Sun all do SACK.)
R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: ober...@es.net Phone: +1 510 486-8634
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