Hi, I have own AS and established BGP peering with upstream provider. All works fine, but I have /21 IP range and I use only one /24 subnet. Other subnets are unused. When everyone make communications to unused subnet, then make routing loop between my router and upstream bgp router. What is failed?

Hi Milan, the problem is that your ISP is sending you traffic to unused part of /21 and you don't have NULL route / any route that is matched, so you are using 0.0.0.0 and send it back to ISP, and he sends it back to you again
If you will put on interface IP x.x.x.x/21 problem will disapear, our you can create smth. like NULL route in Mikrotik, here is topic about it - http://forum.mikrotik.com/viewtopic.php?f=6&t=2413

Thank you for your reply. Yes, I created null route.

Thank you for your reply. Yes, I created null route.

Have you tried to trace the traffic to the /21 network with traceroute from an outside network?
You do advertise the /24 network to the upstream BGP router, correct?