Running Linux (5th Edition) by Matthias Kalle Dalheimer; Matt Welsh

Author:Matthias Kalle Dalheimer; Matt Welsh
Language: eng
Format: mobi
Tags: Reference:Computers
ISBN: 9781600330384
Publisher: O'Reilly Media
Published: 2009-02-08T10:00:00+00:00

PAP and CHAP

Some ISPs may require you to use a special authentication protocol, such as PAP (Password Authentication Protocol) or CHAP (Challenge Handshake Authentication Protocol) . These protocols rely on some form of "shared secret" known to both the client and the server; in most cases, this is just your ISP account password.

If PAP or CHAP is required by your ISP, they are configured by adding information to the files /etc/ppp/pap-secrets and /etc/ppp/chap-secrets, respectively. Each file has four fields separated by spaces or tabs. Here is an example of a pap-secrets file:

# Secrets for authentication using PAP

# client server secret IP or Domain

mdw * my-password

The first field is your system's name as expected by the remote system—usually your ISP username. The second field specifies the ISP's server name; an asterisk allows this entry to match all ISP servers to which you might connect. The third field specifies the shared secret provided by your ISP; as stated earlier, this is usually your ISP password. The fourth field is primarily used by PPP servers to limit the IP addresses to which users dialing in have access. These addresses can be specified as either IP addresses or domain names. For most PPP client configurations, however, this field is not required.

The chap-secrets file has the same four fields, but you need to include an entry other than * for the service provider's system; this is a secret the ISP shares with you when you establish the account.

If PAP or CHAP is being used, it's not necessary for the chat script to include handshaking information after CONNECT is received; pppd will take care of the rest. Therefore, you can edit /etc/ppp/my-chat-script to contain only the following lines:

#!/bin/sh

# my-chat-script: a program for dialing up your ISP

exec chat -v \

'' ATZ \

OK ATDT555-1212 \

CONNECT ''

You will also need to add the user option to the pppd command line in /etc/ppp/ppp-on, as so:

#!/bin/sh

# the ppp-on script

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