iptables

root@controller31:~# iptables -n -L -t nat --line-number
Chain PREROUTING (policy ACCEPT)
num  target     prot opt source               destination
1    DNAT       tcp  --  0.0.0.0/0            192.168.2.31         tcp dpt:21 to:192.168.2.32
2    DNAT       tcp  --  0.0.0.0/0            192.168.2.32         tcp dpt:21 to:192.168.2.31

Chain INPUT (policy ACCEPT)
num  target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
num  target     prot opt source               destination

Chain POSTROUTING (policy ACCEPT)
num  target     prot opt source               destination
root@controller31:~# iptables -D PREROUTING 2
iptables: No chain/target/match by that name.
root@controller31:~# iptables -t nat -D PREROUTING 2
root@controller31:~# iptables -t nat -D PREROUTING 1