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Chapter 16. If your PPP server uses PAP (Password Authentication Protocol)

If the server to which you are connecting requires PAP or CHAP authentication, you have a little bit more work.

To the above options file, add the following lines

#
# force pppd to use your ISP user name as your 'host name' during the
# authentication process
name <your ISP user name>       # you need to edit this line
#
# If you are running a PPP *server* and need to force PAP or CHAP
# uncomment the appropriate one of the following lines. Do NOT use 
# these is you are a client connecting to a PPP server (even if it uses PAP
# or CHAP) as this tells the SERVER to authenticate itself to your
# machine (which almost certainly can't do - and the link will fail).
#+chap
#+pap
#
# If you are using ENCRYPTED secrets in the /etc/ppp/pap-secrets
# file, then uncomment the following line.
# Note: this is NOT the same as using MS encrypted passwords as can be
# set up in MS RAS on Windows NT.
#+papcrypt

16.1. Using MSCHAP

Microsoft Windows NT RAS can be set up to use a variation on CHAP (Challenge/Handshake Authentication Protocol). In your PPP sources tar ball, you will find a file called README.MSCHAP80 that discusses this.

You can determine if the server is requesting authentication using this protocol by enabling debugging for pppd. If the server is requesting MS CHAP authentication, you will see lines like:-

rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <auth chap 80> <magic 0x46a3>]

The critical information here is auth chap 80.

In order to use MS CHAP, you will need to recompile pppd to support this. Please see the instructions in the README.MSCHAP80 file in the PPP source file for instructions on how to compile and use this variation.

You should note that at present this code supports only Linux PPP clients connecting to an MS Windows NT server. It does NOT support setting up a Linux PPP server to use MSCHAP80 authentication from clients.