Let's ask this question properly.

On a FreeBSD system with a loopback network interface …

% ifconfig lo0 
lo0
 link up loopback drv_running running multicast
 nd6 performnud auto_linklocal no_radr
 link rxcsum txcsum hwcsum rxcsum_ipv6 txcsum_ipv6
 link address metric 0 mtu 16384 
 type 24 linkstate 0 physical 0 baudrate 0 
 inet4 address 127.0.0.1 prefixlen 8 bdaddr 127.0.0.1 
 inet6 address ::1 scope 0 prefixlen 128 bdaddr ::1 scope 0 
 inet6 address fe80::1 scope 3 prefixlen 64 
 inet6 address ::2 scope 0 prefixlen 128 
 inet4 address 127.53.0.1 prefixlen 8 bdaddr 127.53.0.1 
 inet4 address 127.53.1.1 prefixlen 8 bdaddr 127.53.1.1 
%

… pinging the IP address 127.0.0.2, which is not assigned to that (or to any other) network interface results in failure:

% ping -c 1 127.0.0.2 
PING 127.0.0.2 (127.0.0.2): 56 data bytes
ping: sendto: Network is unreachable

--- 127.0.0.2 ping statistics ---
1 packets transmitted, 0 packets received, 100.0% packet loss
% 

The same is true for OpenBSD:

% ping -c 1 127.0.0.2 
PING 127.0.0.2 (127.0.0.2): 56 data bytes
ping: sendto: Network is unreachable
ping: wrote 127.0.0.2 64 chars, ret=-1
--- 127.0.0.2 ping statistics ---
1 packets transmitted, 0 packets received, 100.0% packet loss
% 

But on Linux where there is similarly no 127.0.0.2 configured …

% ifconfig lo
lo
 link up loopback running
 link address 00:00:00:00:00:00 bdaddr 00:00:00:00:00:00 
 inet4 address 127.0.0.1 prefixlen 8 bdaddr 127.0.0.1 
 inet4 address 127.53.0.1 prefixlen 8 bdaddr 127.255.255.255 
 inet6 address ::2 scope 0 prefixlen 128 
 inet6 address fe80:: scope 1 prefixlen 10 
 inet6 address ::1 scope 0 prefixlen 128 
% 

… the ping is surprisingly successful:

% ping -c 1 127.0.0.2
PING 127.0.0.2 (127.0.0.2) 56(84) bytes of data.
64 bytes from 127.0.0.2: icmp_seq=1 ttl=64 time=0.044 ms

--- 127.0.0.2 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.044/0.044/0.044/0.000 ms
% 

How come?

Related questions

• "When does an IP address not need to be assigned to a network interface?" — the very roundabout question, asking for an explanation of "virtual interfaces", that this question asks straightforwardly


• "How is it possible to send ping to all 127.0.0.0/8 successfully?" — several questions in one, rather than one question per question, and not in fact answered by the purported duplicate


• "why such behavior in Linux Network over Loopback Interface" — a question about why on Linux the lo interface seems to also control the pingability of IP addresses that are assigned to other network interfaces (behaviour that is similarly not what one gets on the BSDs)


• "What happens to local LAN traffic on linux to non-loopback addresses?" — a question about non-loopback behaviour

Oh yes it does.

• Jonathan de Boyne Pollard (2019). ifconfig. nosh Guide. Softwares.