Avaya Business Secure Router 252 Configuration - Basics Manuel d'utilisateur télécharger pdf (Page 241)

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Chapter 13 VPN 241

Nortel Business Secure Router 252 Configuration — Basics

Diffie-Hellman (DH) Key Groups

Diffie-Hellman (DH) is a public-key cryptography protocol that allows two

parties to establish a shared secret over an unsecured communications channel.

Diffie-Hellman is used within IKE SA setup to establish session keys. 768-bit

(Group 1 - DH1), 1 024-bit (Group 2 – DH2) and 1 536-bit (Group 5 - DH5)

Diffie-Hellman groups are supported. Upon completion of the Diffie-Hellman

exchange, the two peers have a shared secret, but the IKE SA is not authenticated.

For authentication, use preshared keys.

Perfect Forward Secrecy (PFS)

Enabling PFS means that the key is transient. The key is thrown away and

replaced by a brand new key using a new Diffie-Hellman exchange for each new

IPSec SA setup. With PFS enabled, if one key is compromised, previous and

subsequent keys are not compromised, because subsequent keys are not derived

from previous keys. The (time consuming) Diffie-Hellman exchange is the

trade-off for this extra security.

This can be unnecessary for data that does not require such security, so PFS is

disabled (None) by default in the Business Secure Router. Disabling PFS means

new authentication and encryption keys are derived from the same root secret

(which can have security implications in the long run) but allows faster SA setup

(by bypassing the Diffie-Hellman key exchange).

Configuring advanced Branch office setup

Select one of the VPN rules in the VPN Summary screen and click Edit to

configure the rule. The basic IKE rule setup screen displays.

In the VPN Branch Office Rule Setup screen, click the Advanced button to

display the VPN Branch Office Advanced Rule Setup screen.

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Avaya Business Secure Router 252 Configuration - Basics Manuel d'utilisateur Page 241

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