Does IDS/IPS go Before or After the Firewall?

One of the most common questions people have about intrusion detection systems (IDS) is where to place them on their network. More specifically, many new users are curious whether IDS is more effective when placed before or after the firewall. In this blog post, we will look at the differences in firewalls, IDS, and IPS tools, and weigh the benefits and challenges of placing an IDS/IPS both before and after the firewall.

Does IDS/IPS go before or after a firewall?

The ideal placement for an intrusion detection/prevention system depends on your specific network security needs and resource limitations. There are two main approaches:

IDS after the Firewall (Most Common):

• Advantages:

 - Reduced Load on IDS: The firewall acts as a first filter, blocking a significant portion of unwanted traffic before it reaches the IDS. This improves the efficiency of the IDS by focusing its resources on analyzing legitimate traffic for suspicious activity.

 - Focus on Internal Threats: Placing the IDS inside the network allows it to monitor for malicious activity originating from within as well as external threats that bypassed the firewall.

• Disadvantages:

 - Potential Security Gap: Malicious traffic that slips through the firewall could reach the IDS before being blocked.

IDS before the Firewall (Less Common):

• Advantages:

 - Early Detection: This provides the potential to know about threats before they even reach the firewall, offering an extra layer of protection.

 - Reduced Network Load: Blocking some threats before they enter the internal network can lessen the overall load on network resources.

• Disadvantages:

 - Increased Resource Consumption: The IDS will need to analyze all incoming traffic, including a larger volume of unwanted traffic, potentially impacting performance.

 - Limited Visibility into Internal Threats: Primarily focuses on external threats.

Here are some additional factors to consider:

• Network Size and Complexity: For larger networks with complex traffic patterns, placing the IDS after the firewall can be more efficient.
• Security Priorities: If internal threats are a major concern, placing the IDS inside the network might be more important.
• IDS capabilities: Some advanced IDS systems, like Suricata, can handle the increased load of being placed before the firewall.

Ultimately, the best placement depends on your specific situation. It's recommended to consult with a network security professional to determine the optimal placement for your network environment.

What is the difference between a firewall and IDS?

The main difference between a firewall and an IDS/IPS is that a firewall is simply a control mechanism, while a signature-based intrusion detection system actually detects and alerts on potentially malicious traffic. Firewalls enforce a set of pre-defined rules to permit or deny traffic flow based on characteristics like IP addresses, ports, protocols, or applications. It allows only authorized traffic through the network perimeter.

IDS is a monitoring and detection system. It analyzes network traffic for malicious activity or suspicious patterns that might indicate an ongoing attack. IDS doesn't directly block traffic but raises alerts for further investigation and potential response by security personnel. However, some IDS solutions, like Suricata, can be configured to function as an IPS. In this instance, the IPS can actually block traffic much like a firewall. Some organizations opt to use an IPS instead of a firewall, while others use a firewall and an IDS together.

Where should intrusion detection systems be placed?

Intrusion detection systems (IDS) can be placed at various locations depending on what kind of activity they are monitoring:

• Network Intrusion Detection Systems (NIDS): These are typically placed at strategic points within a network, often behind firewalls at the network perimeter [2]. This allows them to monitor incoming and outgoing traffic and flag any suspicious activity attempting to breach the network. NIDS can also be placed internally to monitor for threats from within the network, such as compromised accounts or insider attacks.
• Host-based IDS: These are installed directly on individual devices like servers or desktops. They monitor the system's activity for malicious programs or unauthorized access attempts.

What are the differences between IDS and IPS?

The difference between IDS and IPS is that IPS actively blocks threats while IDS simply provides alerts. Both systems serve a purpose in an organization’s strategy and come with their own benefits and challenges.

• Intrusion Detection System (IDS): Intrusion detection system software continuously analyzes network traffic or system activity for suspicious patterns that might indicate an ongoing attack. These patterns can be identified through signature-based detection, which matches traffic against known attack signatures, or anomaly-based detection, which looks for deviations from regular behavior. Upon detecting suspicious activity, an IDS can raise alerts, log events, and provide valuable insights for security personnel to investigate and respond to potential threats.
• Intrusion Prevention System (IPS): An IPS extends the functionality of IDS by actively taking steps to prevent intrusions. Based on predefined security policies and identified threats, an IPS can block malicious traffic, terminate suspicious connections, or otherwise disrupt the attacker's progress. This can involve techniques like packet filtering, which blocks unwanted traffic based on pre-defined rules, or deep packet inspection, which examines the content of packets for malicious payloads. It is important to note that one of the challenges with IPS is the possibility of non-malicious traffic being blocked based on a “false positive”

Explore a modern alternative

You need a network security platform that doesn’t generate an endless stream of useless alerts across part of your network, and instead automatically identifies alerts of interest and notifies you of only serious and imminent threats. Your organization deserves response-ready detection with visibility into your entire network regardless of the environment with easy access to all the contextual evidence you need to stop an attack before it can cause damage. Replace your legacy IDS with a modern network detection and response platform that gives you these features and more.

The Stamus Security Platform™ is a network-based threat detection and response solution that eliminates the challenges of legacy IDS while lowering your response time. Stamus Security Platform harnesses the full potential of your network, bringing state-of-the-art threat detection, automated event triage, and unparalleled visibility to the security team.

Book a demo to see if the Stamus Security Platform is right for your organization.

To learn more about replacing your legacy IDS, check out the following resources:

• A Practical Guide for Migrating from Your Legacy IDS/IPS to a Modern Alternative
• 12 Signs It's Time to Upgrade your Legacy IDS/IPS
• 3 Critical Questions to Answer Before a Legacy IDS/IPS Upgrade
• Weak Attack Signals your Legacy IDS will Miss

To be notified of new blog posts and other news, make sure to subscribe to the Stamus Networks blog, follow us on Twitter, LinkedIn, and Facebook, or join our Discord.