Hi Stephen, I didn't look into source, but I suppose there could be different variables / classes to hold IP address and IP subnet. I do it similar way in may programs. Just add interval flag, as stated in error message, into your map / set definition and it would work. > map forward_out { > type ipv4_addr : verdict > } map forward_out { type ipv4_addr : verdict flags interval } in single line rule for nft / libnftables it is done by add map ip <table> forward_out { type ipv4_addr : verdict; flags interval; } ---- S pozdravem / Best Regards Vaclav Zindulka