Date: Tue, 9 Jul 2013 08:48:08 +0000 (UTC) From: Gabor Pali <pgj@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-all@freebsd.org, svn-doc-head@freebsd.org Subject: svn commit: r42215 - head/en_US.ISO8859-1/htdocs/news/status Message-ID: <201307090848.r698m8Uq018589@svn.freebsd.org>
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Author: pgj Date: Tue Jul 9 08:48:08 2013 New Revision: 42215 URL: http://svnweb.freebsd.org/changeset/doc/42215 Log: - Add a Q2 report on improved TCP SYN cookies Submitted by: andre Modified: head/en_US.ISO8859-1/htdocs/news/status/report-2013-04-2013-06.xml Modified: head/en_US.ISO8859-1/htdocs/news/status/report-2013-04-2013-06.xml ============================================================================== --- head/en_US.ISO8859-1/htdocs/news/status/report-2013-04-2013-06.xml Tue Jul 9 08:33:48 2013 (r42214) +++ head/en_US.ISO8859-1/htdocs/news/status/report-2013-04-2013-06.xml Tue Jul 9 08:48:08 2013 (r42215) @@ -18,7 +18,7 @@ <!-- XXX: keep updating the number of entries --> <p>Thanks to all the reporters for the excellent work! This report - contains 28 entries and we hope you enjoy reading it.</p> + contains 29 entries and we hope you enjoy reading it.</p> <!-- XXX: set date for the next set of submissions --> <p>The deadline for submissions covering between July and September 2013 @@ -1579,4 +1579,84 @@ functionality through <tt>pkg(8)</tt>.</ and <tt>CAP_RECV_RIGHTS</tt>.</task> </help> </project> + + <project cat='kern'> + <title>Improved TCP SYN Cookies</title> + + <contact> + <person> + <name> + <given>Andre</given> + <common>Oppermann</common> + </name> + <email>andre@FreeBSD.org</email> + </person> + </contact> + + <links> + <url href="http://docs.freebsd.org/cgi/getmsg.cgi?fetch=28838+0+current/freebsd-net">Description</url>; + <url href="http://people.freebsd.org/~andre/syncookie-20130708.diff">Patch</url>; + </links> + + <body> + <p>We have had a SYN cookie implementation for quite some time now + but it has some limitations with current realities for window + scaling and SACK encoding the in the few available bits.</p> + + <p>This patch updates and improves SYN cookies mainly by:</p> + + <ol> + <li>Encoding of MSS, WSCALE (window scaling) and SACK into the + ISN (initial sequence number) without the use of timestamp + bits.</li> + + <li>Switching to the very fast and cryptographically strong + SipHash-2-4 hash MAC algorithm to protect the SYN cookie + against forgery.</li> + </ol> + + <p>The common parameters used on TCP sessions have changed quite a + bit since SYN cookies very invented some 17 years ago. Today we + have a lot more bandwidth which makes the use window scaling + almost mandatory. Also SACK has become standard as it makes + recovering from packet loss much more efficient.</p> + + <p>The original SYN cookies method only stored an indexed MSS + values in the cookie. This obviously is not sufficient anymore + and breaks in the presence of WSCALE. WSCALE information is + only exchanged during SYN and SYN-ACK. If we cannot keep track + of it then we severely underestimate the available send or + receive window, compounded with the fact that with large window + scaling the window size information on the TCP segment header + would be even lower numerically.</p> + + <p>A number of years back SYN cookies have been extended to store + the additional state in the TCP timestamp fields, if available + on a connection. It has been adopted by Linux as well. While + timestamps are common among the BSD, Linux and other Unix + systems, Windows never enabled them by default, thus they are + not present for the vast majority of clients seen on the + Internet.</p> + + <p>The new improvement in this patch moves all necessary + information into the ISN again removing the need for timestamps. + Both the MSS and send WSCALE are stored in 3 bit indexed form + together with a single bit for SACK. While we cannot represent + all possible MSS and WSCALE values, both are 16 bit fields in + the TCP header, in only 3 bits each this, it turns out, is not + actually necessary.</p> + + <p>These improvements allow one to run with SYN cookies only on + Internet-facing servers. However while SYN cookies are + calculated and sent all the time, they are only used when the + syn cache overflows due to attacks or overload. In that cause + though, you can rest assured that no significant degradation in + TCP connection setup happens anymore and that even Windows + clients can make use of window scaling and SACK.</p> + </body> + + <help> + <task>Additional testing on busy servers.</task> + </help> + </project> </report>
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