Compatible-systems 5.4 Manuel d'utilisateur télécharger pdf (Page 173)

Chapter 10 - WAN Link Protocols 167

PPP Link from the Link Type pulldown in the Link Configuration: WAN

Dialog Box (under WAN/Link Configuration), and then clicking on the

CHAP button at the bottom of the dialog box.

CHAP is a security protocol that allows devices using PPP to authenticate

their identities to each other through the use of a message digest (MD5) calcu-

lation. Either or both ends of a link can request that the opposite end of the

link authenticate itself. CHAP requests do not depend on knowing which

device initiated a call, so a calling device can request and/or provide authen-

tication, as can a device that receives a call.

CHAP authentications can be performed at any time after a communications

link is connected. A CHAP authentication sequence begins with a “chal-

lenge” from one end of the link. The challenge includes the name of the chal-

lenging router.

The response to the challenge includes the name of the responding router.

This name will be looked up in the challenging router’s database or on a

configured RADIUS server. The name, along with a “secret” value that is

stored in the database or RADIUS server and is shared by both ends, will be

processed by the challenging end using the MD5 algorithm.

If the result of an identical MD5 calculation performed by the challenging end

is not the same, the challenging end drops the link.

To access the User Authentication Database Configuration Dialog Box, select

Global/User Authentication Database in the Device View. To access the

RADIUS Configuration Dialog Box, select Global/System Configuration in

the Device View and click on the RADIUS button.

v Note: Because the secret is never passed across the link, even in encrypted

form, CHAP is considered to be significantly more secure than PAP.

Request CHAP Authentication

This checkbox controls whether this router will send a CHAP challenge to the

other end before allowing PPP negotiation to complete. Each challenge will

include this router’s Name (as described below), along with a random value

selected by this router.

• If checked this router will send a CHAP challenge to the device at the

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Compatible-systems 5.4 Manuel d'utilisateur Page 173