Specifications

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Cisco Security Appliance Command Line Configuration Guide
OL-6721-01
Chapter 1 Introduction to the Security Appliance
VPN Functional Overview
VPN Functional Overview
A VPN is a secure connection across a TCP/IP network (such as the Internet) that appears as a private
connection. This secure connection is called a tunnel. The security appliance uses tunneling protocols to
negotiate security parameters, create and manage tunnels, encapsulate packets, transmit or receive them
through the tunnel, and unencapsulate them. The security appliance functions as a bidirectional tunnel
endpoint: it can receive plain packets, encapsulate them, and send them to the other end of the tunnel
where they are unencapsulated and sent to their final destination. It can also receive encapsulated
packets, unencapsulate them, and send them to their final destination. The security appliance invokes
various standard protocols to accomplish these functions.
The security appliance performs the following functions:
• Establishes tunnels
• Negotiates tunnel parameters
• Authenticates users
• Assigns user addresses
• Encrypts and decrypts data
• Manages security keys
• Manages data transfer across the tunnel
• Manages data transfer inbound and outbound as a tunnel endpoint or router
The security appliance invokes various standard protocols to accomplish these functions.
Security Context Overview
You can partition a single security appliance into multiple virtual devices, known as security contexts.
Each context is an independent device, with its own security policy, interfaces, and administrators.
Multiple contexts are similar to having multiple standalone devices. Many features are supported in
multiple context mode, including routing tables, firewall features, IPS, and management. Some features
are not supported, including VPN and dynamic routing protocols.
In multiple context mode, the security appliance includes a configuration for each context that identifies
the security policy, interfaces, and almost all the options you can configure on a standalone device. The
system administrator adds and manages contexts by configuring them in the system configuration,
which, like a single mode configuration, is the startup configuration. The system configuration identifies
basic settings for the security appliance. The system configuration does not include any network
interfaces or network settings for itself; rather, when the system needs to access network resources (such
as downloading the contexts from the server), it uses one of the contexts that is designated as the admin
context.
The admin context is just like any other context, except that when a user logs into the admin context,
then that user has system administrator rights and can access the system and all other contexts.
Note You can run all your contexts in routed mode or transparent mode; you cannot run some contexts in one
mode and others in another.
Multiple context mode supports static routing only.