snakebite.net and blackhole.snakebite.net domains don't exist anymore, but test_timeout uses it:

    def testConnectTimeout(self):
        # Testing connect timeout is tricky: we need to have IP connectivity
        # to a host that silently drops our packets.  We can't simulate this
        # from Python because it's a function of the underlying TCP/IP stack.
        # So, the following Snakebite host has been defined:
        blackhole = resolve_address('blackhole.snakebite.net', 56666)
        (...)

If I recall properly, snakebite.net was a service provided by Trent Nelson to test CPython on various operating systems (Solaris, IRIX, HP-UX, etc.). It seems like the service is now completely down.

Article from 2009:

https://conferences.oreilly.com/oscon/oscon2009/public/schedule/detail/8268

"Snakebite is a culmination of ten months of secretive work, seven trips to Michigan State University, six blown fuses and about $60,000. The end result? A network of around 37-ish servers of all different shapes and sizes, specifically geared towards the development needs of open source projects. Get the inside scoop from Snakebite's Founder, Trent Nelson, and MSU Director Dr. Titus Brown."