RedHat: UDP send to more than 1024 different IPs in a sequence fails

I faced a strange behaviour of UDP socket on RadHat 7.5: I send a 10 bytes buffer to many different dummy IPs 192.168.1.1, 192.168.1.2 etc. I do this in a cycle with no delays. I send to the same port for every IP (the port number doesn't affect the result). When I send to IP with sequence number 1025 or more - send always fails with error "Invaild Argument".

My small test is written in C++, sending using sendto() function.

When I added a small delay of 10 ms between sends - the problem has gone.

Any ideas? Looks like the socket object in Kernel has buffers for every IP and the maximum number of buffers is 1024.