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When I run my web crawler for 100,000 domains, a lot of DNS queries are made via UDP, and my ISP blocks my traffic thinking I am doing a DDoS attack. Is it possible to configure Linux to use TCP instead of UDP for DNS lookup queries? This needs to be done in a transparent way at the layer of GLIBC so I would not need to change the application.

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Put use-vc in /etc/resolv.conf (since glibc 2.14)

                Sets RES_USEVC in _res.options.  This option forces the
                 use of TCP for DNS resolutions.

http://man7.org/linux/man-pages/man5/resolv.conf.5.html

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    Sidenote: Simply add the line options use-vc
    – maowtm
    Jun 4, 2019 at 15:01

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