This is undesirable because it causes the dual-stack client to have a worse user. You need to pick the preferred protocol (it is IPv6 by default) and it will only 'fall back' on DNS lookup failure, not on connectivity failure. Happy Eyeballs: Success with Dual-Stack Hosts When a server's IPv4 path and protocol are working, but the server's IPv6 path and protocol are not working, a dual-stack client application experiences significant connection delay compared to an IPv4-only client.
PING, in particular, will not fall back at all. Individual applications must support the fallback function.
#HAPPY EYEBALLS WINDOWS#
This functionality is also implemented in curl, iOS, Android, etc With IPv6-only network connectivity becoming increasingly common, misconfigurations in DNS servers can cause requests to fail, even when connectivity is available through alternative servers. Happy Eyeballs is not implemented globally in the Windows XP stack. The client orders these to alternate between IPv6 and IPv4 addresses, starting with IPv6. In the browser, this is handled for you using the Happy Eyeballs algorithm.Contributed by rueda on from the ecstatic-nostrils dept. A client has a list of a server’s IP addresses, containing both IPv6 and IPv4 addresses. unwind(8) gains Happy Eyeballs-like flexibility.Happy Eyeballs is the fun name of RFC 6555, which is a clever hack to deploy IPv6 even if some client’s IPv6 connectivity is unstable. A possible logical extension would be implementing the algorithm in other applications.I’ve been working on OkHttp’s Happy Eyeballs and exploring testing strategies along the way. Possible extensionĪt the moment happy eyeballs relates to the web browser. Referring to the web browser, what happy eyeballs does is introducing a different TCP behavior after a response to the DNS query is received.īoth IPv6 and IPv4 syn packets are sent off at the same time, the first syn-ack that reaches the source will determined the protocol used and the other one will be discarded. Connection Timeout The primary purpose of Happy Eyeballs is to reduce the wait time for a dual-stack connection to complete, especially when the IPv6 path is broken and IPv6 is preferred.
There is clearly too much “waiting time”! Happy eyeballs algorithm RFC 8305 Happy Eyeballs v2 December 2017 6. If Happy Eyeballs is widely deployed in the future, this recommendation might be revisited. Only when TCP is sure that this tentative of connection has failed will send the IPv4 (or IPv6) syn. In a dual stack connection model, an IPv6 (or IPv4) syn will first be sent. The introduction of the dual stack environment, which deals with both IPv4 and IPv6 addresses, has made this performance issue worse. Algorithm Requirements A 'Happy Eyeballs' algorithm has two primary goals: 1. He main issue here is that if the syn-ack gets lost or is not sent at all, TCP keeps waiting slowing down all applications that are related to that connection. RFC 6555 Happy Eyeballs Dual Stack April 2012 4. The behavior happy eyeballs is trying to improve is generated by how the TCP handshake protocol works.īefore establishing a connection and after sending a syn packet, TCP waits a syn-ack packet from the counterpart. The default timeout from the moment the first IPv6 connect is issued until the first IPv4 starts, is 200 milliseconds. This makes curl prefer a quick IPv6 connect. The idea of Happy eyeballs was first introduced as improvement to the responsiveness of the dual-stack applications (both IPv4 and IPv6). For hosts having both IPv6 and IPv4 addresses, curl will first fire off the IPv6 attempt and then after a timeout, start the first IPv4 attempt.
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