1. What is the difference between a packet-filtering firewall and a proxy-server firewall? Can the two be used together? 2. What are the four tables maintained by the Linux kernel for processing incoming and outgoing packets?
3. How does an iptables based firewall decide as to which packets to subject to the INPUT chain of rules, which to the FORWARD chain of rules, and which to the OUTPUT chain of rules? Additionally, which part of a packet is examined in order to figure out whether or not the condition part of a rule is satisfied?
4. Show how you would use the iptables command to reject all incoming SYN packets that seek to open a new connection with your machine?
5. What is the option given to the iptables command to flush all the user-defined chains in a table? How do you flush all the rules in a table?
6. What are the icmp-types associated with the echo-request (ping) and with the echo-reply (pong) packets?
7. What is the iptables command if you want your machine to accept only the incoming connection requests for the SSHD server you are running on your machine? (You want your machine to drop all other connection request packets from remote clients.)
8. What is connection tracking? How does an iptables-based firewall know that the incoming packets all belong to the same ongoing connection?