hi, My system is Ubuntu 13.04, kernel version is 3.8.0-21-generic, bird version is 1.4.4. Device configuration is as follows: 1. about function function rt_import (int asn; int set peer_asns; prefix set peer_nets) { if (net ~ peer_nets) then return false!; } 2. about filter filter bgp_upstream { if rt_import (64609, [64609], [192.168.1.0/24]) then reject; } In the above function, I use net ~ peer_nets to filter out peer_nets route, but in filter medium, peer_nets defined as 192.168.1.0/24, which would lead to such a fine route 192.168.1.1 will be filtered out. If the test using the "-" operator, will lead filter to filter out all the routes. Why? In the above example, how can I use "operators" to achieve peer_nets defined as 192.168.1.0/24, 192.168.1.1 subnet address to ensure it will not be filtered out. Thank you very much for nothing always help, thanks.