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Linux PPP HOWTO

Robert Hart, hartr@interweft.com.au

Copyright

This document is distributed under the terms of the GPL (GNU Public License).

Distribution

This document will be posted to comp.os.linux.answers as new versions of the document are produced. It is also available in HTML format at:-

• Linux Howto Index
• PPP-HOWTO

Other formats (SGML, ASCII, postscript, DVI) are available from Howtos - other formats.

As sunsite.unc.edu carries a very heavy load, please use an appropriate mirror site close to you.

Acknowledgements

A growing number of people have provided me with assistance in preparing this document. Special thanks go to Al Longyear for the guidance on PPP itself (if there are mistakes here, they are mine not his), Greg Hankins (maintainer of the Linux Howto system)and Debi Tackett (of MaximumAccess.com) for many helpful suggestions on style, content order, logic and clarity of explanations.

Finally, to the many people who have contacted me by email offering comments - my thanks. As with all HOWTO authors, the satisfaction of helping is all the payment we receive and it is enough. By writing this HOWTO I am repaying in a small way the debt I - and all other Linux users - owe to the people who write and maintain our OS of choice.

1. Introduction

• 1.1 Clients and Servers
• 1.2 Differences between Linux distributions
• 1.3 Distribution specific PPP configuration tools

2. IP Numbers

3. Aims of this Document

• 3.1 Setting up a PPP Client
• 3.2 Linking two LANs or a LAN to the Internet using PPP
• 3.3 Setting up a PPP server
• 3.4 Using PPP over a direct null modem connection
• 3.5 This document at present does NOT cover...

4. Software versions covered

5. Other Useful/Important Documents

• 5.1 Useful Linux Mailing Lists

6. Overview of what has to be done to get PPP working as a client

• 6.1 Obtaining/Installing the software
• 6.2 Compiling PPP support into the kernel
• 6.3 Obtaining information from your ISP
• 6.4 Configuring your modem and serial port
• 6.5 Setting up Name to Address Resolution (DNS)
• 6.6 PPP and root Privileges
• 6.7 Checking your distribution PPP Files and setting up the PPP Options
• 6.8 If your PPP server uses PAP (Password Authentication Protocol)
• 6.9 Connecting to the PPP server by hand
• 6.10 Automating your PPP Connection
• 6.11 Shutting down the link
• 6.12 If you have problems
• 6.13 After the link comes up
• 6.14 Problems with standard IP services on a Dynamic IP number PPP link

7. Configuring your Linux Kernel

• 7.1 Installing the Linux Kernel source
• 7.2 Knowing your hardware
• 7.3 Kernel compilation - the Linux 1.2.13 kernel
• 7.4 Kernel compilation - the Linux 1.3.x and 2.0.x kernels
• 7.5 Note on PPP-2.2 and /proc/net/dev
• 7.6 General kernel config considerations for PPP

8. Getting the Information you need about the PPP server

9. Configuring your modem and serial port

• 9.1 A note about serial ports and speed capabilities
• 9.2 Serial Port Names
• 9.3 Configuring your modem
• 9.4 Note on Serial Flow Control
• 9.5 Testing your modem for dial out

10. Setting up Name to Address Resolution (DNS)

• 10.1 The /etc/resolv.conf file
• 10.2 The /etc/host.conf file

11. Using PPP and root privileges

12. Setting up the PPP connection files

• 12.1 The supplied options.tpl file
• 12.2 What options should I use? (No PAP/CHAP)

13. If your PPP server uses PAP (Password Authentication

• 13.1 Using MSCHAP
• 13.2 The PAP/CHAP secrets file
• 13.3 The PAP secrets file
• 13.4 The CHAP secrets file
• 13.5 Handling multiple PAP-authenticated connections

14. Setting up the PPP connection manually

15. Automating your connections - Creating the connection scripts

• 15.1 Connection scripts for User name/Password Authentication
• 15.2 The ppp-on script
• 15.3 Editing the supplied PPP startup scripts
• 15.4 What a Chat script means...
• 15.5 A chat script for PAP/CHAP authenticated connections
• 15.6 The pppd debug and file option_file options

16. Testing your connection script

17. Shutting down the PPP link

18. Debugging

• 18.1 I have compiled PPP support into the kernel, but...
• 18.2 My modem connects but ppp never starts up
• 18.3 The syslog says "serial line is not 8 bit clean..."
• 18.4 Default route not set
• 18.5 Other Problems

19. Getting Help when totally stuck

20. Common Problems once the link is working

• 20.1 I can't see beyond the PPP server I connect to
• 20.2 I can send email, but not receive it
• 20.3 Why can't people finger, WWW, gopher, talk etc to my machine?

21. Using Internet services with Dynamic IP numbers

• 21.1 Setting up email
• 21.2 Setting Up a local Name server

22. Linking two networks using PPP

• 22.1 Setting up the IP numbers
• 22.2 Setting up the routing
• 22.3 Network security

23. After the link comes up - the /etc/ppp/ip-up script

• 23.1 Special routing
• 23.2 Handling email queues
• 23.3 A sample /etc/ppp/ip-up script
• 23.4 Handling email

24. Using /etc/ppp/ip-down

25. Routing issues on a LAN

• 25.1 Note on Security

26. Setting up a PPP server

• 26.1 Kernel compilation
• 26.2 Overview of the server system
• 26.3 Getting the software together
• 26.4 Setting up standard (shell access) dialup.
• 26.5 Setting up the PPP options files
• 26.6 Setting pppd up to allow users to (successfully) run it
• 26.7 Setting up the global alias for pppd

27. Using PPP across a null modem (direct serial) connection