 |
|
Please Whitelist This Site?
I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)
If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.
If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.
Thanks for your understanding!
Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide
|
|
|
Custom Search
|
|
IPSec Security Associations and the Security Association Database (SAD); Security Policies and the Security Policy Database (SPD); Selectors; the Security Parameter Index (SPI)
(Page 1 of 2)
Woah, there sure is a lot of "security" stuff in that topic title. Those items are all closely related, and important to understand before we proceed to looking at the core IPSec protocols themselves. These constructs are used to guide the operation of IPSec in a general way and also in particular exchanges between devices. They control how IPSec works and ensure that each datagram coming into or leaving an IPSec-capable device is properly treated.
Where to start… where to start. J Let's begin by considering the problem of how to apply security in a device that may be handling many different exchanges of datagrams with others. There is overhead involved in providing security, so we do not want to do it for every message that comes in or out. Some types of messages may need more security, others less. Also, exchanges with certain devices may require different processing than others.
To manage all of this complexity, IPSec is equipped with a flexible, powerful way of specifying how different types of datagrams should be handled. To understand how this works, we must first define two important logical concepts:
- Security Policies: A security policy
is a rule that is programmed into the IPSec implementation that tells
it how to process different datagrams received by the device. For example,
security policies are used to decide if a particular packet needs to
be processed by IPSec or not; those that do not bypass AH and ESP entirely.
If security is required, the security policy provides general guidelines
for how it should be provided, and if necessary, links to more specific
detail.
Security policies for a device are stored in the device's Security Policy Database (SPD). - Security Associations: A Security Association
(SA) is a set of security information that describes a particular
kind of secure connection between one device and another. You can consider
it a "contract", if you will, that specifies the particular security
mechanisms that are used for secure communications between the two.
A device's security associations are contained in its Security Association Database (SAD).
It's often hard to distinguish the SPD and the SAD, since they are similar in concept. The main difference between them is that security policies are general while security associations are more specific. To determine what to do with a particular datagram, a device first checks the SPD. The security policies in the SPD may reference a particular security association in the SAD. If so, the device will look up that security association and use it for processing the datagram.
|
| |||||||||||||||||||
Home - Table Of Contents - Contact Us
The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.