Why are packets lost?

Question

Ping

There are two addresses 81.22.218.1 and 81.22.218.42, the second is a user who complains about packet loss, but with a direct ping to the gateway, there is no loss.
There is no access to either one or the other "piece of iron".
What will be the assumptions?

Answer 1

which complains about packet loss

What does it mean? What kind of packets are lost, how does it manifest itself?
As I understand it, the address 81.22.218.1 uses a router. Do not expect a router to respond to 100% "pings" (icmp or udp packets). The router may have special filtering active (control plane protection policy in the cisco world), which in some cases cannot be disabled.