Network security is essential for businesses to safeguard their digital infrastructure against cyber threats. But strong security isn’t built on a single tool or control; it requires protecting every layer involved in data transmission. From physical connections to application-level traffic, each layer of the OSI model plays a role in keeping networks reliable, available, and secure.
Layer 3, also called the network layer, is the backbone of data communication, handling IP addressing, routing, and packet forwarding. When left vulnerable, it can expose the entire network to risk, enabling malicious actors to intercept, reroute, block, or impersonate traffic between networks. From routing-based attacks to IP spoofing, this layer presents critical challenges, but with the right strategies, organizations can stay ahead of threats and ensure secure data delivery.
What is OSI Layer 3?
The Open Systems Interconnection (OSI) model is a conceptual framework that standardizes how different networking protocols communicate. It consists of seven distinct layers, each responsible for specific functions. Layer 3, the network layer, ensures data transfer across different networks by handling routing, forwarding, and logical addressing. When a device sends data, the network layer uses IP addresses to determine the best path for the data to travel to its destination.
The primary protocol operating at the network layer is the Internet Protocol (IP), which ensures data packets are correctly addressed and routed to their destination. Additional protocols at this layer support routing decisions, network diagnostics, and secure data transmission.
What Are the Functions of Layer 3?
The network layer plays a crucial role in enabling communication between different networks. Its primary job is to transfer data across network boundaries using IP addresses. To do this, it adds an IP header to each data packet that contains both the source and destination IP addresses, ensuring end-to-end delivery. But Layer 3 does more than just route data; it also manages traffic flow, prioritizes service quality, and adapts packets for transport across diverse networks.
Here are the key functions that take place at this layer:
- Routing: Uses routing protocols to determine the best path for data transmission. Routers operate at this layer, directing packets between networks based on destination IP addresses.
- Packet Forwarding: Moves packets from one network interface to another. Ensures delivery by referencing information about neighboring networks and available paths.
- Addressing: Assigns and uses IP addresses to identify devices across networks and ensure accurate data delivery.
- Routing Tables: Maintains and updates routing tables to enable efficient and accurate routing decisions.
- Fragmentation and Reassembly: Breaks down large packets into smaller fragments to accommodate network limitations, then reassembles them at the destination.
- Quality of Service (QoS): Helps maintain consistent performance by prioritizing traffic and managing how packets are handled during transmission, especially under limited bandwidth or high traffic conditions.
These functions work together to ensure reliable, secure, and efficient data transmission between networks.
What Are the Common Layer 3 Network Protocols?
While layer 3 relies on several protocols to enable data transmission, the two most prominent are the Internet Protocol (IP) and the Internet Control Message Protocol (ICMP).
Internet Protocol (IP)
IP is the primary protocol used at this layer. If DNS is the internet’s address book, then IP is the postal service that reads the address and delivers the data to the right house. The IP protocol assigns unique addresses to devices and manages logical addressing to enable communication between systems across different networks.
IP is also responsible for packet forwarding; it does this by selecting paths for data to travel across routers until it reaches its destination. The two main versions of IP are:
- IPv4 uses 32-bit addresses to create numerical addresses such as 192.0.2.0
- IPv6 uses 128-bit addresses to create long-form hexadecimal addresses such as 2001:0db8:85a3:0000:0000:8a2e:0370:7334
Notably, the Internet Assigned Numbers Authority (IANA) officially ran out of free IPv4 addresses, and today the protocol relies on life-extending technologies such as Network Address Translation (NAT). While IPv6 boasts near-limitless capacity, global adoption has been slower than anticipated.
Internet Control Message Protocol (ICMP)
To continue the addressing analogy: If IP is the postal service that reads the address and delivers the data to the right house, then ICMP is the delivery failed notice.
ICMP works alongside IP to perform network diagnostics and error reporting. It’s used by tools like ping and traceroute to test connectivity, detect unreachable destinations, identify packet loss, or diagnose routing loops. While ICMP doesn’t transmit user data, it plays a critical role in maintaining and troubleshooting network health.
Together, protocols support end-to-end packet delivery, traffic routing, and network visibility, making them essential for stable and scalable network communication. Unlike layer 2 protocols, which operate within a single network segment, layer 3 protocols enable communication between networks.
What Is the Difference Between the OSI Model and the TCP/IP Model?
The OSI and TCP/IP models both describe how network communication works, but they differ in structure and origin.
The OSI model is a conceptual framework developed in the late 1970s and formally adopted by the International Organization for Standardization (ISO) in 1984. It divides network communication into seven distinct layers, each responsible for specific functions, from the physical transmission of data to high-level application interactions.
In contrast, the Transmission Control Protocol/Internet Protocol (TCP/IP) model uses a more streamlined, four-layer architecture and serves as the foundation of the modern internet. Its Internet layer handles functions similar to the OSI model’s Network Layer, with a primary focus on IP-based communication.
While the TCP/IP model is more commonly used in real-world implementations, the OSI model remains a valuable reference and teaching tool. IT professionals, engineers, and developers continue to use it to conceptualize, design, and troubleshoot networking functions across all seven layers.
Why is Securing Layer 3 Difficult?
Securing layer 3 is challenging because it sits at the intersection of routing, addressing, and traffic flow. The very features that make this layer powerful (and essential) also make it a high-value target for attackers.
One of the core complexities lies in IP addressing. Every device connected to a network needs an IP address, and Layer 3 handles how those addresses are assigned and recognized. The sheer number of addressable devices increases the surface area for attacks, making centralized control difficult.
Another challenge with IP addressing is IP headers, which guide data packets to their destination. If malicious actors tamper with these headers, they can reroute traffic and steer users to phishing sites designed to harvest credentials or other sensitive information. Maintaining header integrity is critical to keeping data secure, but it presents a significant operational challenge. Routing protocols like Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP) help direct traffic through intermediate routers. But if not properly secured, malicious actors can manipulate these protocols to hijack traffic or destabilize routing paths.
Finally, Layer 3 is a common target for Distributed Denial of Service (DDoS) attacks, which flood routers and endpoints with massive volumes of traffic, overwhelming infrastructure and disrupting legitimate communication. Defending against DDoS attacks requires significant infrastructure, as the size and complexity of these attacks continue to grow. For example, DigiCert’s UltraDDoS Protect recently blocked a massive DDoS attack that reached 2.4 Terabits per second (Tbps) of bandwidth and 553 Million packets per second (Mpps) of impact, the largest attack today against the UltraDDoS Protect Network.
Best Practices for Implementing Layer 3 Security
Layer 3 security is essential for protecting traffic as it moves across networks. Because this layer handles IP addressing, routing, and packet forwarding, it’s a common target for attacks like spoofing, protocol manipulation, and DDoS. Securing this layer requires a mix of architectural strategies, intelligent traffic management, and layered defenses.
Use Network Address Translation (NAT)
NAT does more than extend the life of IPv4 addresses; it also modifies IP headers to allow multiple devices within a local area network (LAN) to share a single public IP address. This conserves address space and obscures internal network details, making it more difficult for attackers to target individual devices directly.
Implement Port Address Translation (PAT)
A subtype of NAT, PAT assigns unique source ports to each session, enabling even more devices to communicate externally using a single IP. This helps enforce session isolation and adds an additional layer of obscurity and control.
Deploy Load Balancing to Manage Traffic
Load balancing isn’t just about optimizing network performance. Modern load balancing techniques, such as DNS-based, global server load balancing (GSLB), or anycast routing, play a key role in network-layer resiliency. In the context of layer 3 security, load balancing helps:
- Reduce latency and congestion by routing traffic to the closest or least-loaded resource
- Mitigate DDoS attacks by absorbing and dispersing volumetric floods across distributed nodes
- Maintain uptime during traffic spikes or targeted disruptions
WAF, WAAP, and DDoS Mitigation Services
While Web Application Firewalls (WAFs) and Web Application and API Protection (WAAP) platforms were built for application-layer protection, they play a critical supporting role in defending against layer 3–7 threats:
- WAFs sit in front of web applications and inspect HTTP requests, blocking known exploits like SQL injection, XSS, and HTTP floods.
- WAAPs extend WAF functionality with API security, bot management, and DDoS mitigation that covers Layers 3, 4, and 7.
- A purpose-built DDoS mitigation service can detect and mitigate both volumetric layer 3 floods and stealthy layer 7 HTTP floods, preventing service degradation even when bandwidth limits aren’t exceeded.
These solutions are most effective when deployed in tandem with other best practices to create a multi-layered defense strategy.
Don’t Leave Layer 3 Exposed: Secure Every Layer
Layer 3 security is essential for building strong, resilient networks. Given the critical role this layer plays in data transmission, it will continue to be a prime target for cyber attacks. But with proven defenses and a proactive approach, your organization can harden its infrastructure and keep network traffic secure.
Our integrated WAF and WAAP solutions offer robust, application-aware protection against threats like common application layer threats, even in complex workflows and API-driven environments.
Need protection beyond the network layer? See how we protect Layer 7 as well.
Our UltraDDoS Protect solution defends the network layer with over 15 Tbps of DDoS traffic ingestion capacity, backed by a global footprint and 24/7 expert mitigation support. Whether it’s HTTP flood attacks or multi-vector campaigns, UltraDDoSProtect helps absorb and neutralize the most aggressive DDoS threats.
Looking to reinforce your layer 3 security strategy? Contact us today.
