CURLOPT_INTERFACE(3) Library Functions Manual CURLOPT_INTERFACE(3)
NAME
CURLOPT_INTERFACE - source interface for outgoing traffic
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_INTERFACE, char *interface);
DESCRIPTION
Pass a char pointer as parameter. This sets the interface name to use as
outgoing network interface. The name can be an interface name, an IP ad-
dress, or a hostname. If you prefer one of these, you can use the fol-
lowing special prefixes:
* if!<name> - Interface name * host!<name> - IP address or hostname *
ifhost!<interface>!<host> - Interface name and IP address or hostname
If if! or ifhost! is specified but the parameter does not match an ex-
isting interface, CURLE_INTERFACE_FAILED is returned from the libcurl
function used to perform the transfer.
libcurl does not support using network interface names for this option
on Windows.
We strongly advise against specifying the interface with a hostname, as
it causes libcurl to do a blocking name resolve call to retrieve the IP
address. That name resolve operation does not use DNS-over-HTTPS even
if CURLOPT_DOH_URL(3) is set.
The application does not have to keep the string around after setting
this option.
Using this option multiple times makes the last set string override the
previous ones. Set it to NULL to disable its use again.
DEFAULT
NULL, use whatever the TCP stack finds suitable
PROTOCOLS
This functionality affects all supported protocols
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode res;
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
curl_easy_setopt(curl, CURLOPT_INTERFACE, "eth0");
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
HISTORY
The if! and host! syntax was added in 7.24.0.
The ifhost! syntax was added in 8.9.0.
AVAILABILITY
Added in curl 7.3
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,
see libcurl-errors(3).
SEE ALSO
CURLOPT_LOCALPORT(3), CURLOPT_SOCKOPTFUNCTION(3), CURLOPT_TCP_NODELAY(3)
libcurl 2026-07-12 CURLOPT_INTERFACE(3)
Generated by dwww version 1.16 on Sat Oct 3 05:05:58 CEST 2026.