Migrating from PHP 5.6.x to PHP 7.0.x
PHP Manual

Changes in SAPI Modules

FPM

Unqualified listen ports now listen on both IPv4 and IPv6

In PHP 5, a listen directive with only a port number would listen on all interfaces, but only on IPv4. PHP 7 will now accept requests made via both IPv4 and IPv6.

This does not affect directives which include specific IP addresses; these will continue to only listen on that address and protocol.


Migrating from PHP 5.6.x to PHP 7.0.x
PHP Manual