The mystery of the century, where does the ping between hosts come from?

Question

linux

client 10.20.41.91/8
server:
1 interface 10.1.0.80/8
2nd 10.20.40.5/24
Problem: the client quietly pings 10.20.40.5 - why?
Both do not have routes, packet forwarding is disabled on the server, the firewall is disabled.

Answer 1

From the client's point of view, 10.20.40.5 is on his subnet. He can send a package to him directly. The return answer arrives because the arp tables already have a bunch of ip-mac for 10.20.41.91 and they are apparently connected by a switch.