Why are the packets from the knock client arriving in random order?

Question

linux

I use knock under Windows and under Linux, I
run
knock -v myip 6000 7000 8000 9000
as standard I watch with a sniffer or tcpdump packets are sent in the right order
Answers come already
randomly , in the right order can come once out of 10 or 20 attempts.
That is, I send
knock -v myip 6000 7000 8000 9000
And the sequence 8000 9000 7000 6000 comes.
It seems that some order of packets is turned off in the kernel to increase acceleration
. The server with knockd is spinning on ubuntu 14.04 checked on two different servers in different data centers.
Testing clients from different points from Windows and from Linux.
I didn't tune the network stack in sysctl, I just turned off ipv6, but it didn't seem to have any effect.

Answer 1

Send over TCP, which guarantees delivery in the correct order.

Answer 2

these are network and routing delays. I observed such an effect when sending via a mobile network. And sometimes they come right, sometimes they don't. An output - ports TCP + selection of timeouts on the server and on the client.