CURLOPT_DNS_INTERFACE(3)

💅 CURLOPT_DNS_INTERFACE(3) — the curl library functions manual, bestie edition 🎀

okay so real talk, this page lives in the libcurl corner of the manual (the Library Functions Manual one), and it's about CURLOPT_DNS_INTERFACE(3). yes that's the whole title. slay. let's get into it ✨

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🦋 NAME

CURLOPT_DNS_INTERFACE — the interface to speak DNS over, periodt

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🌸 SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DNS_INTERFACE, char *ifname);

that's it. that's the whole vibe check. handle is your curl handle, ifname is the interface name, and it comes back at you as a CURLcode. 🫶

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💖 DESCRIPTION

so you pass a char pointer as the parameter, and what it does is set the name of the network interface that the DNS resolver should bind to. key detail, bestie: it has to be an interface name, not an address. like "eth0" energy, not "192.168.1.5" energy. do not mix those up, i'm literally begging 🙈

and if you set this option to NULL, it just goes back to the default setting, which is not binding to a specific interface at all. freedom. no cap.

also, good news: the application does not have to keep the string around after setting this option. you can let it go, she's fine, she's got her own copy 💅

setting this option multiple times? the last string you set overrides all the previous ones. last one wins, main character energy only 👑. and setting it to NULL disables its use again.

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🍓 DEFAULT

NULL

(no interface bound, just vibes 🌈)

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🔥 PROTOCOLS

this functionality affects all supported protocols. all of them. every single one. iconic ⭐

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✨ EXAMPLE

here's the whole thing, copy it exactly, don't @ me:

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
    curl_easy_setopt(curl, CURLOPT_DNS_INTERFACE, "eth0");
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

look at her go, binding DNS to eth0 and fetching https://example.com/foo.bin. we love a functional snippet 🧚

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💀 NOTES

⚠️ okay this is the important caveat so listen up: this option requires that libcurl was built with a resolver backend that supports this operation. and the c-ares backend is the only such one.

so if you're not on c-ares, this option is giving nothing. literally nothing. check your build first bestie 😭

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🎀 AVAILABILITY

Added in curl 7.33.0. vintage. a classic 💜

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🌟 RETURN VALUE

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK. non-zero means an error occurred — go check libcurl-errors(3) for the tea 🍵.

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🦋 SEE ALSO

• CURLOPT_DNS_LOCAL_IP4(3)
• CURLOPT_DNS_LOCAL_IP6(3)
• CURLOPT_DNS_SERVERS(3)
• CURLOPT_INTERFACE(3)

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okay that's the whole page, you're officially educated 💖 this was libcurl, dated 2026-10-12, and the page was CURLOPT_DNS_INTERFACE(3) — go bind an interface, stay hydrated, and remember: interface name, not address. mwah 🫶✨