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Chapter 12
Introduction to IPSec
VPN Overview
12.1
A VPN (Virtual Private Network) provides secure communications between sites without the
expense of leased site-to-site lines. A secure VPN is a combination of tunneling, encryption,
authentication, access control and auditing technologies/services used to transport traffic over the
Internet or any insecure network that uses the TCP/IP protocol suite for communication.
12.1.1
IPSec
Internet Protocol Security (IPSec) is a standards-based VPN that offers flexible solutions for secure
data communications across a public network like the Internet. IPSec is built around a number of
standardized cryptographic techniques to provide confidentiality, data integrity and authentication
at the IP layer.
12.1.2
Security Association
A Security Association (SA) is a contract between two parties indicating what security parameters,
such as keys and algorithms they will use.
12.1.3
Other Terminology
Encryption
Encryption is a mathematical operation that transforms data from "plaintext" (readable) to
"ciphertext" (scrambled text) using a "key". The key and clear text are processed by the
encryption operation, which leads to the data scrambling that makes encryption secure.
Decryption is the opposite of encryption: it is a mathematical operation that transforms
"ciphertext" to plaintext. Decryption also requires a key.
This chapter introduces the basics of IPSec VPNs.
Contivity 221 VPN Switch User's Guide
12-1
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