What Is an Original IP Packet?

Updated on September 29, 2025

An Original IP Packet refers to the initial, unencapsulated IP packet that a host or application generates for transmission across a network. This term is most often used in the context of network security and tunneling protocols, where a new IP packet is created to carry the original one inside of it.

The original packet contains the fundamental data and header information from the sender, while the new packet’s purpose is to facilitate secure or controlled delivery across an intermediate network. Understanding the distinction between the original and the new, encapsulated packet is critical for troubleshooting network tunnels, such as those used in Virtual Private Networks (VPNs) and Internet Protocol Security (IPsec).

Network administrators and security professionals encounter this concept when implementing secure communication channels between distributed networks. The original IP packet represents the actual communication intent, while the encapsulating packet serves as the transport mechanism through potentially untrusted networks.

Definition and Core Concepts

The original IP packet is the network-layer data unit created by a host’s Transmission Control Protocol/Internet Protocol (TCP/IP) stack. It consists of two primary components:

• IP Header: This section contains the source and destination IP addresses, the Time-to-Live (TTL), the protocol number (e.g., TCP, User Datagram Protocol), and other fields necessary for routing the packet.
• Payload: The data portion of the packet, which typically contains a higher-layer protocol segment (e.g., a TCP segment with application data).

In the context of encapsulation and tunneling, the original IP packet is the payload of a new, external IP packet. The new packet has its own header and is responsible for routing the traffic across the tunnel, while the original packet remains untouched inside.

Foundational Concepts

• Encapsulation: The process of wrapping one data unit inside another. This technique allows protocols to transport data across networks that might not natively support the original protocol.
• Tunneling: A technique used to route one network protocol over another. A tunnel is the logical connection created for this purpose, enabling secure or controlled communication across intermediate networks.
• IPsec Tunnel Mode: The IPsec protocol suite uses a tunnel mode where the entire original IP packet is encrypted and placed inside a new IP packet for transport. This mode provides complete protection of the original packet’s header and payload.

How It Works

The concept of an original IP packet is best understood by examining the encapsulation process used in a VPN tunnel. This step-by-step process demonstrates how the original packet is preserved and transported.

• Packet Generation: A host on a private network (e.g., 192.168.1.10) wants to send data to a server on a different private network (10.0.0.50). The host generates an original IP packet with the source IP 192.168.1.10 and the destination IP 10.0.0.50.
• Encapsulation at the Gateway: The packet arrives at the VPN gateway. The gateway recognizes that this traffic needs to be sent through a secure tunnel based on its routing table and security policies.
• New Packet Creation: The gateway creates a new, external IP packet with distinct characteristics:
  • New IP Header: The source IP of the new header is the public IP of the sending gateway (203.0.113.1). The destination IP is the public IP of the receiving gateway (198.51.100.2).
  • New Payload: The original IP packet (including its header and payload) is placed entirely inside the payload of this new packet.
• Tunnel Transmission: This new, external packet is now routed across the internet to the receiving VPN gateway. The routing infrastructure only sees the external packet headers.
• Decapsulation at the Gateway: The receiving gateway receives the new packet, decrypts it if necessary, and removes the new header. The original IP packet is extracted intact.
• Forwarding: The receiving gateway then forwards the original IP packet to its final destination (10.0.0.50). The final server only ever sees the original packet with its preserved header information.

Key Features and Components

• Header Preservation: The original IP packet’s header is preserved entirely, including its source and destination addresses, TTL, and other fields. This allows the packet to be routed correctly after it is decapsulated at the tunnel endpoint.
• Security: By being encapsulated and often encrypted, the original packet’s contents and metadata are protected from interception in transit. The encapsulation layer can provide authentication, integrity verification, and confidentiality.
• Logical Separation: The original packet represents the logical, end-to-end communication between the actual source and destination. The new packet represents the physical transport across the intermediate network infrastructure.
• Protocol Independence: The encapsulation process is protocol-agnostic, meaning the original packet can contain any valid IP payload, including TCP, UDP, Internet Control Message Protocol (ICMP), or other protocols.

Use Cases and Applications

The concept is central to several key networking and security technologies that network administrators deploy regularly:

• Virtual Private Networks (VPNs): The most common application. The original IP packet is the private network traffic that is encapsulated for secure transmission over the public internet. This enables remote users and branch offices to access corporate resources securely.
• IPsec Tunnels: Used to create secure, encrypted connections between networks or hosts. IPsec tunnel mode completely encapsulates the original packet, providing comprehensive protection against eavesdropping and tampering.
• Generic Routing Encapsulation (GRE): A tunneling protocol that encapsulates a wide variety of network-layer protocols inside IP packets. GRE tunnels are commonly used to connect networks across intermediate infrastructure that doesn’t support the original protocol.
• Software-Defined Networking (SDN) Overlays: Modern networking architectures use encapsulation to create virtual network overlays on top of physical infrastructure, enabling network virtualization and micro-segmentation.

Troubleshooting and Considerations

Network administrators must address several technical challenges when working with encapsulated original IP packets:

• Maximum Transmission Unit (MTU) Issues: When a new header is added, the total packet size increases. This can cause the encapsulated packet to exceed the network’s MTU, leading to fragmentation and performance degradation. Path MTU Discovery and proper MTU configuration are essential for optimal performance.
• Double Encapsulation: In complex network environments, a packet may be encapsulated multiple times, each time adding a new header. This can occur when VPN traffic traverses multiple tunnel segments or when overlay networks are stacked. Double encapsulation can be a source of performance problems and routing complexity.
• Packet Analysis: Network analysis tools like Wireshark are used to examine network traffic. When analyzing tunneled traffic, administrators must examine both the outer (new) and inner (original) IP headers to understand the complete communication path and diagnose connectivity issues.
• Quality of Service (QoS) Implications: QoS policies applied to encapsulated traffic may not properly classify the original packet’s application requirements, since the intermediate network infrastructure only sees the outer headers.

Key Terms Appendix

• Encapsulation: The process of placing a packet inside another, creating a layered protocol structure that enables transport across diverse network infrastructures.
• IPsec: A suite of protocols used to secure Internet Protocol communications through authentication and encryption at the network layer.
• Tunneling: A method of sending data packets through a secure virtual pipe, creating logical connections across physical network boundaries.
• VPN (Virtual Private Network): A secure tunnel that extends a private network over a public one, enabling secure remote access and site-to-site connectivity.
• Payload: The data portion of a packet that contains the actual information being transmitted, distinct from the protocol headers used for routing and control.