is the request done from outside the vm (so port 8010 is forwarded by the VM to the Windows machine) or is it done locally on the Windows machine?
/HH Den ons 27 aug. 2025 kl 15:51 skrev Lars Sunde via curl-library < curl-library@lists.haxx.se>: > Appreciate your response Stefan. > > The current setup is running on Windows 10 (inside a VM) that has one > Ethernet adapter that is configured with IPv6 and IPv4. Both IPv6 and IPv4 > is setup with "Obtain an IPv4/6 address automatically". Using ipconfig I > can see that 192.168.56.102 is assigned which is IPv4 and no IPv6 is > assigned. I believe this is a default Windows 10 setup, so basically a > vanilla Windows setup. > > You mention that Curl has an internal timer. > > - Is this timer used to enforce CURLOPT_CONNECTTIMEOUT and > CURLOPT_TIMEOUT time constraints? > - Is this timer used enforce CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS time > constraints? > > > We use "http://localhost:8010/some/path"; in our test setup. In most test > runs we see that curl uses 200-300 ms to check IPv6 and then moving on to > IPv4 which is quickly resolved to 127.0.0.1 and used to communicate with > server. This is understandable. In some rare cases we see that curl uses > 3-10 seconds to check IPv6 which often causes a timeout. I am struggling to > understand why in *some rare cases *"the system" need so long to fail to > resolve "localhost" on IPv6. I understand it is possible to force Curl to > use IPv4 but do not want to remove IPv6 as an option. Also, If the IPv6 > address is unchecked in ethernet adapter it is still used by Curl which > seems strange. > > Regards, Lars > > ------------------------------ > *Fra:* Stefan Eissing <ste...@eissing.org> > *Sendt:* onsdag 27. august 2025 10:20 > *Til:* libcurl development <curl-library@lists.haxx.se> > *Kopi:* Stenberg Daniel <dan...@haxx.se>; Lars Sunde <laasu...@hotmail.com > > > *Emne:* Re: ipv6 connect timeout > > > > > Am 27.08.2025 um 10:03 schrieb Lars Sunde via curl-library < > curl-library@lists.haxx.se>: > > > > Thanks for the link to the blog which explain part of the problem. > However, when running libCurl 8.5 in a VM on Windows 10 we sometimes see > that "Trying [::1]:8010..." takes upto 10 seconds to complete which is > quite a long time. We have setup curl with CURLOPT_TIMEOUT to 600 seconds, > CURLOPT_CONNECTTIMEOUT to 10 seconds and > CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS to 200. Windows 10 has a "Max SYN > Retransmissions" parameter which is set to 4 in our environment but that > does not really explain the delay. You can see this parameter via "netsh > interface tcp show global" command. > > If your CURLOPT_CONNECTTIMEOUT is 10 seconds, then trying an address for > up to 10 seconds sounds right. > > > > > How is the CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS option implemented in curl? > Does it rely on the OS functionality to respond within a timeframe or does > it use an internal timer? Has there been any changes\bug-fixes to happy > eyeballs algorithm between version 8.5 and 8.15? > > libcurl uses an internal timer. CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS triggers > and, if there are addresses from different ip versions, the other ip > version is attempted in parallel (unless you tell curl explicitly to only > use on ip version). It, by default, starts with ipv6 when available and > CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS triggers the ipv4 attempts. > > If your hostname resolves to a single ipv6 address, this will not do > anything. No other ip family is available, no other address is available. > The single address will be attempted to 10 seconds, unless the OS reports a > failure. > > If the host has several ipv6 addresses, it will attempt each address, one > after the other, with timouts depending on time remaining and addresses > available. Any new attempt closes the previous one of the same ip family. > > This is unchanged in curl < 8.16. In 8.16, the strategy to try different > addresses in the same ip version changes. Ongoing attempts will not be > closed, just new ones added. A hostname with 10 ipv6 addresses might have, > during the connect phase, up to 10 sockets open. The > CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS to start attempts on the other ip version > remains the same. > > Hope this helps, > Stefan > > > > > Regards, LarsFra: Daniel Stenberg <dan...@haxx.se> > > Sendt: fredag 22. august 2025 16:57 > > Til: Lars Sunde via curl-library <curl-library@lists.haxx.se> > > Kopi: Lars Sunde <laasu...@hotmail.com> > > Emne: Re: ipv6 connect timeout On Fri, 22 Aug 2025, Lars Sunde via > curl-library wrote: > > > > > We are running C++ software that uses libCurl 8.5 on Windows 10 and 11 > that > > > perform HTTP operations. > > > > > > During testing I notice a difference in some rare situations when > running > > > the software in Window 11 and in a virtual machine. The virtual > machine is > > > Oracle Virtual Box with Windows 11 host and Windows 10 guest OS). > > > > > > We enabled CURLOPT_VERBOSE to debug the issue when the software > attempts to > > > perform a HTTP post operation. > > > > I suspect you are seeing Windows working as designed. I believe this is > more > > or less the same problem I blogged aobut last year: > > > > https://daniel.haxx.se/blog/2024/08/14/slow-tcp-connect-on-windows/ > > > > -- > > > > / daniel.haxx.se || https://rock-solid.curl.dev > > -- > > Unsubscribe: https://lists.haxx.se/mailman/listinfo/curl-library > > Etiquette: https://curl.se/mail/etiquette.html > > > -- > Unsubscribe: https://lists.haxx.se/mailman/listinfo/curl-library > Etiquette: https://curl.se/mail/etiquette.html >
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