Bug 243234

Summary:	TCP/ECN - RTO retransmissions sent without CWR flag in newreno and cubic
Product:	Base System	Reporter:	Richard Scheffenegger <rscheff>
Component:	kern	Assignee:	Michael Tuexen <tuexen>
Status:	Closed FIXED
Severity:	Affects Some People	CC:	net, rgrimes, rscheff, tuexen
Priority:	---	Keywords:	needs-qa
Version:	CURRENT	Flags:	koobs: mfc-stable12? koobs: mfc-stable11?
Hardware:	Any
OS:	Any
URL:	https://reviews.freebsd.org/D23119

Description Richard Scheffenegger freebsd_committer

2020-01-09 22:19:44 UTC

While investigating performance implications of RTO on ECN-enabled TCP flows, it was noted that the recovery from a lost retransmission - using the RTO timeout - is sent without the CWR flag in the TCP header (but the IP ECT codepoint is cleared).

Linux has a similar misbehavior, but there it appears that someone tied the signaling of TCP ECN header flags to the setting of the IP header ECT codepoints - which is not correct though.

dctcp has explicit code in its _cong_signal handler, to mark the RTO retransmission explicitly with the CWR flag.

Comment 1 Richard Scheffenegger freebsd_committer

2020-01-20 23:09:31 UTC

https://reviews.freebsd.org/D23119

Reviews and comments more than welcome

Comment 2 Michael Tuexen freebsd_committer

2020-01-25 15:23:14 UTC

Fixed in base r357116.