Listen on all IP address (ipv4 and ipv6 dual mode) in single bind by default if not specify '-s'
Create an IPv6 server socket that can also accept IPv4 connections. To do so, create a regular IPv6 socket, turn off the socket option IPV6_V6ONLY, bind it to the "any" address, and start receiving. IPv4 addresses will be presented as IPv6 addresses, in the IPv4-mapped format.
KrazyIvan
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