Curl resolve ipv4, That is name resolving

Curl resolve ipv4, Basically if curl can find an ipv6 address for the domain in your URL, then it'll try to fetch it, and if that fails, curl fails, without falling back on trying the IPv4 address. That is name resolving. Consider it a sort of /etc/hosts alternative provided on the command line. Forcing IPv4 or IPv6 connections with curl helps validate dual-stack deployments, compare performance between address families, and isolate routing or firewall issues. Allows an application to select what kind of IP addresses to use when establishing a connection or choosing one from the connection pool. Using this, you can make the curl requests(s) use a specified address and prevent the otherwise normally resolved address to be used. Jan 12, 2026 · In this guide, we’ll demystify how `curl --resolve` works, why it’s critical when using proxies, and walk through practical examples to fix DNS issues, test staging environments, and bypass misbehaving proxies. Each resolve rule to add should be written using the format [+]HOST:PORT:ADDRESS[,ADDRESS] HOST is the name libcurl wants to resolve, PORT is the port number of the service where libcurl wants to connect to the HOST and ADDRESS is one or more numerical IP addresses. libcurl tries hard to re-use an existing connection rather than to create a new Jul 17, 2012 · How do I force libcurl to access a server running in dual stack mode over either ipv4 or ipv6? It shouldn't be hard to do using IPs addresses, but I'm looking for something that works with DNS Apr 20, 2020 · When IPv6 acts up In rare occasions or even in some setups, you may find yourself in a situation where you get back problematic IPv6 addresses in the name resolve, or the server’s IPv6 behavior seems erratic, your local config simply makes IPv6 flaky or things like that. When talking HTTPS, this sends SNI for the name in the URL and curl verifies the server's response to make sure it serves for the name in the URL. Sep 1, 2016 · Provide a custom address for a specific host and port pair. If you specify multiple IP addresses they need to be separated by comma. Feb 11, 2022 · When preparing to launch a website, or debugging problems with a site that's already live, sometimes it can be helpful to bypass CDN and proxy layers when requesting content from the site by sending those web requests directly to a specific IP address without using the site's public DNS records. CURLOPT_IPRESOLVE - IP protocol version to use. This is interesting when using hostnames that resolve to more than one IP family. Reasons you may want to ask curl to stick to IPv4-only to avoid a headache. Name resolving Most transfers libcurl can do involves a name that first needs to be translated to an Internet address. Oct 31, 2012 · You can see it work using curl -v and you can see that curl adds the resolve option to the DNS cache temporariy, and adds uses the IP address you specified. . 1 This is an issue with curl, which has been fixed by the curl people, but many OS distributions package old versions. The curl command-line tool provides options to force the use of IPv4 or IPv6 addresses. Using a numerical IP address directly in the URL usually avoids the name resolve phase, but in many cases it is not easy to manually replace the name with the IP address. By prefixing the host with a '+' you can make the entry time out after curl's default timeout (1 minute). --resolve inserts the address into curl's DNS cache, so it effectively makes curl believe that is the address it got when it resolved the name. The provided address set by this option is used even if --ipv4 or --ipv6 is set to make curl use another IP version. Aug 28, 2025 · When working with network requests, ensuring compatibility with either IPv4 or IPv6 addresses can be crucial for troubleshooting, consistency, and network configuration.


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