To insert a rule at the top of the iptables tables in Linux, you can use the "--insert" option with the "iptables" command. The "--insert" option allows you to specify the position at which the new rule should be inserted in the chain.
For example, to insert a rule at the top of the "INPUT" chain, you can use the following command:
iptables -I INPUT 1 -p PROTOCOL -i INTERFACE -d DESTINATION -j TARGET
Replace "PROTOCOL" with the protocol of the traffic (e.g., tcp, udp, icmp), "INTERFACE" with the name of the interface (e.g., eth0, wlan0), "DESTINATION" with the destination IP address or network, and "TARGET" with the action to be taken (e.g., ACCEPT, DROP).
For example, to insert a rule that drops incoming traffic from the IP address "192.168.1.100" at the top of the "INPUT" chain, you can use the following command:
iptables -I INPUT 1 -p all -i eth0 -d 192.168.1.100 -j DROP
This will insert the rule as the first rule in the "INPUT" chain .