Happy Eyeballs

Agenda

• Why "Happy Eyeballs"
• Happy Eyeballs vs. traditional IP connections
• Microsoft Windows NCSI
• Happy Eyeballs v3

Happy Eyeballs

Why

• Traditionally, IPv6 capable operating systems prefer IPv6 over IPv4
  • If IPv6 is available, it is tried first
  • If the connection cannot be established, IPv4 will be used after an timeout on the IPv6 connection
• This results in non-optimal user experience

Traditional IPv6 connections

Traditional IPv6 connections (1/9)

Traditional IPv6 connections (2/9)

Traditional IPv6 connections (3/9)

Traditional IPv6 connections (4/9)

Traditional IPv6 connections (5/9)

Traditional IPv6 connections (6/9)

Traditional IPv6 connections (7/9)

Traditional IPv6 connections (8/9)

Traditional IPv6 connections (9/9)

Happy Eyeballs

Happy Eyeballs

RFC 8305 "Happy Eyeballs Version 2: Better Connectivity Using Concurrency" brings a solution

• Try IPv6 and IPv4 connections simultaneously
• IPv6 has a slight head start
• Take the first connection that is established (IPv6 or IPv4)
  • User gets always the fast connection

Happy Eyeballs Implementation

Example implementation:

• Call getaddinfo(), which returns a list of IP addresses sorted by the host's address preference policy.
• Initiate a connection attempt with the first address in that list (e.g., IPv6).
• If that connection does not complete within a short period of time, initiate a connection attempt with the first address belonging to the other address family (e.g., IPv4).
• The first connection that is established is used. The other connection is discarded.

Happy Eyeball in operation (1/4)

Happy Eyeball in operation (2/4)

Happy Eyeball in operation (3/4)

Happy Eyeball in operation (4/4)

Happy Eyeball Implementations

• Google Chrome 11+
• Mozilla Firefox version 13+
• Apple macOS
  • CFSocketStream() Framework
  • Safari
• Apple iOS
• Vivaldi/Brave/Edge/Opera Browser
• Windows 8/10/11

Microsoft Windows "NCSI"

NCSI

Microsoft has developed a slightly different solution for their Windows OS (Version 8+):

• The Windows OS tests IPv6 connectivity on every network change and saves the result per network
• In case no direct IPv6 connection is detected, the IPv6 default route is downgraded (e.g. IPv4 will be preferred for all connections)
• The IPv6 connectivity test is part of the NCSI (Network Connection Status Indicator) network-Icon in the Windows status bar

NCSI (1/7)

NCSI (2/7)

NCSI (3/7)

NCSI (4/7)

NCSI (5/7)

NCSI (6/7)

NCSI (7/7)

IPv6 NCSI test

• The result of a successful IPv6 NCSI connectivity test is stored per network for 30 days
• Negative results are not stored, the test will be repeated once a network configuration parameter changes
• Leaving a "captive WLAN-Portal" triggers a new NCSI test
• If proxy-servers are configured, the NCSI test is skipped

IPv6 NCSI test

• Downgrading the IPv6 "default" route has an effect on all application (not only on the web browser)
• In enterprise environments, the NCSI-test can be redirected to local DNS and Web servers
• Or adjusted using PowerShell Set-NCSIPolicyConfiguration: http://technet.microsoft.com/en-us/library/hh848620(v=wps.620).aspx
• Or disabled with a policy registry setting

NCSI Registry settings

Windows NCSI IPv6 test

• Advantages over "IETF" Happy Eyeballs:
  • Works for all applications
  • Easier to troubleshoot
• Possible downsides
  • Some IPv6 issues could not be detected (some ICMPv6 issues)
  • "Privacy" concerns over "phoning home"
  • NCSI request might be blocked (for privacy reasons) - IPv6 will be downgraded despite full IPv6 connectivity

Happy Eyeballs v3, QUIC and the HTTPS DNS-Record

Happy Eyeballs v3, QUIC and the HTTPS DNS-Record

• HTTP/3 capable clients (Browser, Apps) need to decide to connect to a web server via HTTP3/UDP or HTTP2/TCP
• This decision is similar to the Happy Eyeball IPv6 vs. IPv4 decision

Happy Eyeballs v3, QUIC and the HTTPS DNS-Record

• The HTTPS-Record (RFC 9460) in DNS can give applications guidance on what protocol to choose
• The IETF is working on a 3rd iteration on Happy Eyeballs to take HTTP/3 and the HTTPS record into account: "Happy Eyeballs Version 3: Better Connectivity Using Concurrency" https://datatracker.ietf.org/doc/draft-pauly-v6ops-happy-eyeballs-v3/

Ressources

• RFC 8305 - Happy Eyeballs Version 2: Better Connectivity Using Concurrency https://www.rfc-editor.org/rfc/rfc8305
• Lazy Eye Inspection: Capturing the State of Happy Eyeballs Implementations (2024) https://arxiv.org/pdf/2412.00263
• What is NCSI: http://technet.microsoft.com/en-us/library/cc766017(v=ws.10).aspx

Questions?