# Reachability

As mentioned in [Section 3.2](https://www.usenix.org/system/files/foci20-paper-anonymous_0.pdf), we test the reachability of [the 216 injected IPs](https://gfw.report/publications/foci20_dns/foci20_anonymous/injected_ips/ips_after_drop.txt) from our VPS in China and the United States by initiating TCP handshakes on port 80 and port 443. Specifically, we perform this experiment daily for 7 days (from April 17, 2020 to April 23, 2020) and each days results looked similar.

The result, summarized in [Figure 3](https://www.usenix.org/system/files/foci20-paper-anonymous_0.pdf#page=4), shows only `0.4%` of these IP-port pairs were ever observed to be reachable from China.