Editing Explicit Congestion Notification (section)

====Mac OS X====
[[Mac OS X]] 10.5 and 10.6 implement ECN support for TCP. It is controlled using the Boolean [[sysctl]] variables {{Mono|net.inet.tcp.ecn_negotiate_in}} and {{Mono|net.inet.tcp.ecn_initiate_out}}.<ref name="mac">{{cite web | url = http://www.icir.org/floyd/ecn.html#implementations | title = ECN (Explicit Congestion Notification) in TCP/IP | url-status = live | archive-url = https://web.archive.org/web/20120619200913/http://www.icir.org/floyd/ecn.html#implementations | archive-date = 2012-06-19 }}</ref>  The first variable enables ECN on incoming connections that already have ECN flags set; the second one tries to initiate outgoing connections with ECN enabled. Both variables default to {{Mono|0}},{{Failed verification|date=February 2025}} but can be set to {{Mono|1}} to enable the respective behavior.

In June 2015, [[Apple Inc.]] announced that [[OS X 10.11]] would have ECN turned on by default,<ref name="apple-wwdc-719" /> but the OS shipped without that default behavior. In macOS Sierra, ECN is enabled for half of TCP sessions.<ref>{{cite web|url=https://arstechnica.com/gadgets/2016/09/macos-10-12-sierra-the-ars-technica-review/6/|title=macOS 10.12 Sierra: The Ars Technica review|website=Ars Technica|date=20 September 2016|access-date=25 April 2018|url-status=live|archive-url=https://web.archive.org/web/20180426012040/https://arstechnica.com/gadgets/2016/09/macos-10-12-sierra-the-ars-technica-review/6/|archive-date=26 April 2018}}</ref>