[josephcsible]

I think the weirdness comes from the use of multiple addresses at once, specifically fe80::whatever addresses always being present and getting used even on normal setups when everything's working fine and a global address is configured, as opposed to 169.254.whatever addresses, which most networks never intend to use and so usually only show up when something is wrong.

[nine_k]

Isn't 127/8 always present in IPv4, without I'll consequences?

[josephcsible]

I meant it's one address per interface, and loopback has always been its own interface.

[trumpdong]

One address per host is more common in serious networks that don't have endless IP addresses (10/8 block) allocated to them.

[dcrazy]

There is no problem with allocating one 127.0.0.0/8 to every interface on your host, because 127.0.0.0/8 is only ever accessible to the host itself. So even if you have multi-homed a single routable IPv4 address to 2 NICs on your server (for redundancy), you can still assign 127.0.0.1 to the first and 127.0.0.2 for the second, which you can then use to bind a port to a specific interface in the pair. (I don’t know if anyone actually does this.)

[trumpdong]

How would the receiving host know which 127 address you imagined belongs to it?

[dcrazy]

What do you mean “receiving host?” 127/8 is reserved for loopback. If you bind a socket to an interface with an address in that range, you can only use it to communicate with yourself. The sending and receiving hosts are the same.