::ffff:0:0:0/96— A prefix used for IPv4-translated addresses which are used by the Stateless IP/ICMP Translation (SIIT) protocol.
Stack Overflow user rockerBOO explained:
Windows 7 has IPv6 enabled by default. Even though my server listens on IPv4 only, Windows 7 sends the
::ffff:prefix to the IPv4 as part of the transition to IPv6.
node.js - Express.js req.ip is returning ::ffff:127.0.0.1 - Stack Overflow
IPv6 address - Wikipedia, the free encyclopedia