Duplicate packets

duplicate_packets.nft

#!/usr/sbin/nft -f

# see https://unix.stackexchange.com/questions/740061/how-do-you-duplicate-all-udp-traffic-on-a-port-range-using-nftables/

# sends all duplicated packets to 10.0.0.1
# run this before applying this file
# sudo ip addr add 10.0.0.1/24 dev lo

# clean up with
# sudo ip addr delete 10.0.0.1/24 dev lo
# nft flush ruleset

flush ruleset

table ip mangle {
    chain prerouting {
        type filter hook prerouting priority mangle; policy accept;
        iifname != lo udp dport 8000-8100 dup to 10.0.0.1 device lo notrack
    }

	chain input {
		type filter hook input priority mangle; policy accept;
        iifname lo udp dport 8000-8100 ip daddr set 10.0.0.1 notrack
	}
}