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RE: "Could not resolve host" error only on the multi interface

From: Dmitry Karpov via curl-library <>
Date: Tue, 31 Oct 2023 18:32:49 +0000

I would recommend to try without explicitly setting DNS server and timeout - just to use the default DNS system settings.
Maybe, the "" is not routable in your setup.

Also, I would run Wireshark or tcpdump to see if your DNS queries/response were actually sent/received on the wire.

Dmitry Karpov

-----Original Message-----
From: curl-library <> On Behalf Of Luis Carlos Chalaca Figueira via curl-library
Sent: Tuesday, October 31, 2023 10:08 AM
Cc: Luis Carlos Chalaca Figueira <>
Subject: [EXTERNAL] "Could not resolve host" error only on the multi interface

Hello everybody,

I'm building a web crawler.

Started with python but the need for speed led me to libcurl.

The obstacle I'm having is: when using the multi interface a big part of the the connections cloe because of the error "Could not resolve host:"

What I've tried:

1 - Confirmed that all URLs are correct.

2 - Confirmed that using the easy interface URLs are resolved.

3 - Confirmed that other programs like dig, resolvectl, nslookup can resolve URLs that multi interface couldn't.

4 - Set a "reputable" DNS server doing: curl_easy_setopt(handles[i], CURLOPT_DNS_SERVERS, "");.

5 - In the file /etc/nsswitch.conf, line "hosts: files nDNS[NOTFOUNDED=return] dns" I deleted  [NOTFOUNDED=return].

6 - I've turned verbose on - Doesn't help me much.

I don't know what to do more as it seems a problem inside the library, so i posted here before going digging in the library.

System info:

O.S. - Ubuntu 22.04.3 LTS

Harware - HP HP Pavilion Laptop 14-ce3xxx

Processor - Intel® Core™ i7-1065G7 CPU @ 1.30GHz × 8

libcurl version - 7.81.0

Attached I send the source code file I'm using do debug this problem.

Best Regards,

Luis Figueira

Received on 2023-10-31