Question

Describe the procedure of designing a firewall.

Answer 1

Step 1: Retrieve the Iptables firewall:

Iptables is pre-installed on almost every Linux distribution. You can use this command to retrieve the package: sudo apt-get install iptables

Step 2: Discover what Iptables is already configured to do by default:

Run the iptable L command

Step 3: You can decide to modify the existing rules or instead start afresh:

To start afresh, run this command 

iptables-F

Step 4: Decide which firewall ports to close:

First block all lines of attack by running the following commands:

Block XMAS Packets: iptables -A INPUT -p tcp –tcp-flags ALL ALL -j

DROP

Block null packets: iptables -A INPUT -p tcp –tcp-flags ALL NONE -j

DROP

Block syn-flood packets: iptables -A INPUT -p tcp ! –syn -m state –state

NEW -j DROP

Step 5: Decide which firewall ports to leave open:

Here are some ports you could decide to leave open:

For outgoing connections:

80/tcp for HTTP

53/udp for DNS

443/tcp for HTTPS (secured HTTP)

21/tcp for FTP (File Transfer Protocol)

465/tcp for SMTP (send emails)

25/tcp for Insecure SMTP

22/tcp for SSH (secure connection from computer to computer)

993/tcp&udp for IMAP (receive emails)

143/tcp&udp for Insecure IMAP

9418/tcp for GIT (version control system)

For Incoming connections:

993/tcp&udp for IMAP (receive emails)

143/tcp&udp for Insecure IMAP

110/tcp for POP3 (old way to receive emails)

22/tcp for SSH (secure connection from computer to computer)

9418/tcp for GIT (version control system)

Step 6: Save your firewall configuration

Type the following command to save the settings you’ve configured and

restart your firewall: