Bug 243234 - TCP/ECN - RTO retransmissions sent without CWR flag in newreno and cubic
Summary: TCP/ECN - RTO retransmissions sent without CWR flag in newreno and cubic
Status: New
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: CURRENT
Hardware: Any Any
: --- Affects Only Me
Assignee: freebsd-net mailing list
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2020-01-09 22:19 UTC by Richard Scheffenegger
Modified: 2020-01-10 05:29 UTC (History)
3 users (show)

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Description Richard Scheffenegger 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.