What is the difference between transport and tunnel mode?

The main difference between Transport Mode and Tunnel Mode is how they protect IP packets during transmission.

Transport Mode

• Encrypts only the data (payload) of the IP packet.

• The original IP header remains visible, allowing routers to forward the packet normally.

• It is commonly used for host-to-host communication, where both devices support IPsec directly.

• Since only the payload is encrypted, it has lower overhead and better performance.

Tunnel Mode

• Encrypts the entire original IP packet, including the header, and then adds a new IP header.

• This provides a higher level of security because the original source and destination addresses are hidden.

• It is widely used for site-to-site VPNs and remote-access VPNs, where secure communication between different networks is required.

• The additional encapsulation creates slightly more overhead but offers stronger protection.

In simple terms:

• Transport Mode = Protects only the data.

• Tunnel Mode = Protects the entire packet by encapsulating it inside a new packet.

If you're securing communication between two individual computers, Transport Mode is usually sufficient. If you're connecting entire networks over the internet through a VPN, Tunnel Mode is the preferred choice because it encrypts the complete packet and hides the internal network information.