What is a Firewall and How to Configure it?
A firewall refers to the network security device that can monitor incoming and outgoing network traffic while permitting and blocking data packets per the pre-defined security rules. The firewall's sole purpose is to establish a barrier between the organization's network and the incoming traffic from any external sources. So, it is the one that saves your company's sensitive data and information from any potential cyber threats.
How do Firewalls Work?
Firewalls are responsible for blocking the malicious traffic that might enter your network from external sources. It carefully analyzes the incoming traffic based on its predefined security rules to filter any suspicious activities out. It is the one that can prevent any cybercrimes or data attacks from potential cyber criminals.
So, this is the line of defense that can guard traffic at the computer's entry points, also known as ports. These are the point of contact where the information is generally exchanged with external devices.
Start considering the IP addresses as homes and the port numbers as the rooms within those homes to understand the overall working principle of firewalls. Only the trusted people (source addresses) get to enter the house, which is the destination address here.
But once entered, only a handful of them are allowed to visit specific rooms, which are the destination ports here, as per their granted permission. The owner here will be allowed to enter any room (port), while the others need specific access to enter any rooms within the establishment.
In case of any unauthorized traffic, the firewall will run a thorough scan and try to match it with the pre-defined set of security rules. However, if the incoming traffic fails to match these rules, it will be considered a security risk. And in turn, the firewall will prevent the traffic from entering the internal network.
So, if your company is working with sensitive data and information, then firewall installation is a must. That's because, without the same, any third party can infiltrate and infect the network with malware and conduct DDoS (Distributed-Denial-of-Service) attacks.
How to Configure a Firewall?
Configuring the firewall might seem like an intimidating task. However, if the steps are broken down into more straightforward tasks, the entire mechanism of firewall configuration becomes more manageable. Before jumping into these steps, you must understand the value of consulting a PCI or HIPAA security expert to know more about your security options. Remember that the steps are crucial and can support multiple internal networks while performing stateful packet inspection.
Step 1: Secure the Firewall
If any hacker gets administrative access to the company's firewall, it is a practical "game over" for complete network security. That is why the first step here is to secure the firewall. Refrain from putting any firewall into production if it is not appropriately secured by the following methods:
- Do not forget to conduct a thorough firewall update to the latest firmware
- Disable, delete or rename any default user accounts
- Change all the default passwords
- Ensure to use only complicated and highly secured passwords
- In case of multiple administrators managing the firewall, ensure to create additional administrator accounts with restricted privileges based on their specific responsibilities
- Refrain from sharing any user account details
- Disable the SNMP or simple network management protocol or configure it to use the secure community string
Step 2: Architect IP Addresses and Firewall Zones
Once the firewall is secured, it is time to protect the valuable assets on your network. To do so, you need to identify the assets and plan how the network structure can group them together. That means the assets need to be grouped and placed into the networks or zones depending on their similarities, like function and sensitivity levels.
Let's understand this via an example. All the servers providing facilities over the internet, like email servers, virtual private network (VPN) servers, web servers, etc., need to be positioned within a dedicated zone to allow limited inbound traffic, where this designated zone is named the DMZ or demilitarized zone. Servers like database servers must be placed within the internal server zones as they cannot be accessed directly from the internet. Similarly, point-of-sale devices, voice over Internet protocol systems, workstations, etc. need to be placed within the internal network zones.
However, the more you create these zones, the better you get at securing your network. But it is essential to consider managing these zones, which eventually require a lot of patience, time, and other company resources.
After defining the network zone structure appropriately, you must establish the corresponding IP address scheme. Once done, you must create the firewall zones and assign them to firewall interfaces. As you go on building this network infrastructure, use the VLANs to maintain the level-2 separation between your networks.
Step 3: Configure Your Access Control Lists
Once you are done with the network zones, it is time to configure the access control lists. Why? That is because you need to determine which traffic will get access to the zones and which needs to be blocked.
The permitted traffic will be given access using ACLs or firewall rules called access control lists, which is widely applied to each of your interfaces or the firewall sub-interface. Ensure that the ACLs are specific to the IP destination or the exact source and port numbers as and when possible. In addition, you need to use the “deny all” rule at the end of every ACL to restrict and filter unapproved traffic.
Always apply both the outbound and inbound ACLs to each of your firewall interfaces and sub-interface to filter the approved traffic entering the designated zones. If possible, disable the firewall administration interfaces, including web interfaces secure shell (SSH) and from public access. It will eventually help you to protect your firewall configuration from outside cyber threats. Also, disable all unencrypted protocols for firewall management, including HTTP and Telnet connections.
Step 4: Configure Firewall Services and Logging
Is your firewall capable of acting as the network time protocol (NTP) server, dynamic host configuration protocol (DHCP) server, or intrusion prevention system (IPS)? If yes, you need to configure these services while disabling the ones you do not wish to use. Ensure you understand the PCI DSS requirements and configure the firewall to report your logging server with proper details.
Step 5: Test Firewall Configuration
Once you are configuring the firewall, it is time to test the functionality to determine if it delivers the intended results. For example, verify if the firewall can block unauthorized traffic from entering the designated zones as per the ACL configurations. Also, it is essential to conduct thorough vulnerability scanning and penetration testing.
Once you have done the firewall configuration testing, it will be ready for production. Remember to keep a firewall configuration backup and store it securely to ensure that your hard work is not lost due to hardware failure.
Firewall Management: An Overview
This blog is just an overview to let users understand the significant steps involved in the firewall configuration. However, firewall management and monitoring are the most critical activities to ensure that the same continues functioning as per the rules. It includes performing vulnerability scans, monitoring logs, reviewing rules, etc. Also, ensure to document the processes as and when required while managing the configuration diligently to ensure the ongoing protection of your network.
What Should be Your Next Step?
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Director - IT Solutions Engineering
Rahul Bogala is a seasoned IT leader, responsible for driving IT solutions, Products, Pre-sales, and customer experience. He has a successful track record of solving complex IT solutions. He also acts as a partner alliances leader nurturing partnership relationships & vendor management fostering the organic growth of business Rahul has expertise in designing and implementing solutions around: Network and Infrastructure Security, Server, Storage, and End computing Virtualization and cloud computing