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NetEm seems to be rarely known and used traffic control feature available on Linux.

The linked script allows you to delay sending DNS requests (IP packets with destination port set to 53) on given interface. Normally it is useless, but it may be useful for debugging some hard network-related cases in your software.

The script may also work as a base for other network-related experiments using netem. You can read more about it here: http://man7.org/linux/man-pages/man8/tc-netem.8.html

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