Netlink is a flexible, robust, wire-format communications channel typically used for kernel to user communication although it can also be used for user to user and kernel to kernel communications.
There are a wide range of tools available for measuring network performance. Common ones are:
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In the "Delaying only some traffic" section of this page, the following code is given as an example of how to create a delay to just one ip address:
Short list of conferences with Linux networking related attendees:
Page based on Documentation/networking/ip-sysctl.txt.