error when running 127.0.0.1 but not localhost code example

Example: why localhost is not working while 127.0.0.1 works

127.0.0.1       localhost
127.0.1.1       vagrant.vm      vagrant

# The following lines are desirable for IPv6 capable hosts
#::1     localhost ip6-localhost ip6-loopback
::1     ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
127.0.2.1 w1 w1