Answering my own questions. There is a hard-coded list of RFC 1918 addresses that are commonly used as routers that the program tries first to see if they are

Answering my own questions. There is a hard-coded list of RFC 1918 addresses that are commonly used as routers that the program tries first to see if they are faster than gstatic.com. https://github.com/apenwarr/blip/commit/b284f922b047e90321126787b119d2195748a0f8 https://github.com/apenwarr/blip/commit/b284f922b047e9032112... Instead of apenwarr.ca, the code tries a bunch of sites from measurementlab.net: https://github.com/apenwarr/blip/commit/20f99c1d641e8cc607b63d3cb574ed4262fce5c6 https://github.com/apenwarr/blip/commit/20f99c1d641e8cc607b6... The DNS checkbox does the following: Generate a pseudorandom hostname for each test and looks it up in DNS. The hostname happens to be in a domain that returns a valid IP (incidentally always the same one) for every hostname you ask for. This triggers a new HTTP connection, but also validates that your DNS is working reliably without weird dropouts. I made it optional for two reasons: it hits your DNS server pretty hard, which is more rude than blip is usually; and DNS is surprisingly crappy, so you might want to turn it off while looking to see if you have *non* DNS related problems. https://github.com/apenwarr/blip/commit/0678d0668c14e2c7a7f0445cfce32bdaac1dd32e https://github.com/apenwarr/blip/commit/0678d0668c14e2c7a7f0... https://github.com/apenwarr/blip/commit/4a1640977303f6dc58db85ffe06fb3b8e7ab5eef https://github.com/apenwarr/blip/commit/4a1640977303f6dc58db...