Tunneling is the process of encapsulating network packets of one protocol inside the packets of another. For secure remote access, this is the fundamental mechanism used by Virtual Private Networks (VPNs). A remote user, already connected to the Internet, initiates a VPN connection which creates a secure, encrypted "tunnel" to the organization's internal network. The user's private network traffic is encapsulated within public Internet packets, protecting its confidentiality and integrity as it traverses the untrusted public network. This allows the remote user to securely access internal resources as if they were directly connected to the local network.

A. Spoofing: This is a malicious technique used to impersonate another device or user by falsifying data, not a method for establishing a legitimate, secure connection.

B. Packet sniffing: This is the act of intercepting and logging traffic passing over a network. It is a form of eavesdropping and a threat that secure tunneling is designed to prevent.

D. Packet filtering: This is a firewall security function that controls network traffic based on rules. It is a network-side control, not a process initiated by a remote user to create a secure session.

1. National Institute of Standards and Technology (NIST) Special Publication 800-77

Guide to IPsec VPNs. (November 2005). Section 2.1

"IPsec VPNs

" page 2-1. The document states

"IPsec can be used to create a secure channel between... a host and a security gateway... This secure channel is often referred to as a security association (SA) or a tunnel."

2. National Institute of Standards and Technology (NIST) Special Publication 800-113

Guide to SSL VPNs. (July 2008). Section 2.2

"SSL VPNs

" page 2-2. It explains

"Once a user connects to the SSL VPN

a secure tunnel is established between the user’s web browser and the SSL VPN."

3. Saltzer

J. H.

& Kaashoek

M. F. (2009). Principles of Computer System Design: An Introduction. Morgan Kaufmann. Chapter 10

"Networking

" Section 10.5.3

"Virtual Private Networks and Tunnels

" page 448. The text describes tunneling as a method to "carry a packet from a guest protocol by encapsulating it within a packet of a host protocol

" which is the core principle of a VPN.

4. Kurose

J. F.

& Ross

K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. Chapter 8

"Security in Computer Networks

" Section 8.7.2

"IPsec and Virtual Private Networks (VPNs)

" page 747. The text describes IPsec's tunnel mode

which is used for VPNs to create a secure connection between a remote host and a security gateway.