---
name: "CURLOPT_INTERFACE"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_INTERFACE"
---

# CURLOPT\_INTERFACE(3)

source interface for outgoing traffic

## 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 address, or a hostname. If you prefer one of these, you can use the following 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 existing 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)](/CURLOPT_DOH_URL/3.md)* 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 result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
    curl_easy_setopt(curl, CURLOPT_INTERFACE, "eth0");
    result = 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)](/curl_easy_setopt/3.md)* returns a CURLcode indicating success or error.

CURLE\_OK (0) means everything was OK, non-zero means an error occurred, see *[libcurl-errors(3)](/libcurl-errors/3.md)*.

## SEE ALSO

[**CURLOPT\_LOCALPORT**(3)](/CURLOPT_LOCALPORT/3.md), [**CURLOPT\_SOCKOPTFUNCTION**(3)](/CURLOPT_SOCKOPTFUNCTION/3.md), [**CURLOPT\_TCP\_NODELAY**(3)](/CURLOPT_TCP_NODELAY/3.md)