Linux PPP FAQ

Al Longyear, longyear@netcom.com

1. Preface

2. General information

• 2.1 What is PPP?
• 2.2 My university (company) does not support PPP. Can I use PPP?
• 2.3 Where is PPP?
• 2.4 I just obtained PPP. What do I do with it?
• 2.5 Where are additional sources of information for PPP?
• 2.6 Would someone please send me scripts for PPP so that I may see how they are written?
• 2.7 Where should I post questions about PPP?
• 2.8 The PPP software doesn't work. HELP!!!

3. Other implementations

• 3.1 Do you know of a implementation for PPP other than Linux? I would like one for HP-UX, or AIX, or ... (you fill in the blank)?
• 3.2 Did you know that there is a program called \dp\?
• 3.3 What RFCs describe the PPP protocol?

4. Compatibility

• 4.1 Can PPP talk to a SLIP interface?
• 4.2 Which is better? PPP or SLIP?
• 4.3 Is CHAP or PAP better for authentication?
• 4.4 What about CHAP which Microsoft uses with Windows NT?

5. Authentication files

• 5.1 What goes into the /etc/ppp/pap-secrets file? Do you have a sample? Or, my ISP requires that I use PAP. How do I do that?
• 5.2 What goes into the /etc/ppp/chap-secrets file? Do you have a sample?

6. Construction problems

• 6.1 I get compile errors when I try to compile the kernel

7. Problems running pppd

• 7.1 pppd says that version 0.0.0 is out of date
• 7.2 pppd says that that the kernel is not configured for PPP. I know that I enabled the option and built the kernel.
• 7.3 pppd wont run unless you are root
• 7.4 unable to create pid file: no such file or directory
• 7.5 /etc/ppp/options: no such file or directory
• 7.6 Could not determine local IP address
• 7.7 Could not determine remote IP address
• 7.8 I keep getting the message to the effect that the magic number is always NAKed. The system will not connect.
• 7.9 protocol reject for protocol fffb
• 7.10 The PPP software connects, sends quite a few frames, but still does not seem to connect. Why is that?
• 7.11 The /etc/ppp/ip-up scripts won't work.
• 7.12 I can't execute /etc/ppp/ip-up: Exec format error
• 7.13 How do I use PPP with a system which uses dynamic IP assignments? It assigns a different IP address to me with each call.
• 7.14 How do I know what IP address was given to me when it is dynamically assigned?
• 7.15 I just upgraded my system and now pppd reports that the option -v is not supported. Why?
• 7.16 The pppd process reports that it won't replace the existing default route. How do I get it to use the default route?
• 7.17 When I run pppd it says that support is not in the kernel.
• 7.18 How do I use PPP and a local network at the same time?
• 7.19 Can I use the same local IP address for each line of a PPP server?
• 7.20 How do I find my local IP address??
• 7.21 I can't connect to the merit network.

8. DIP

• 8.1 DIP does not have support for PPP\s mode
• 8.2 DIP dies immediately when I do \mode ppp\

9. Process termination

• 9.1 Is there a \dip -k\ for PPP?
• 9.2 PPP does not hangup the modem when it terminates

10. Data Transfer related issues

• 10.1 The ftp transfers seems to die when I do a \put\ operation. They will work correctly if I \get\ a file. Why?
• 10.2 How do I use XON/XOFF for flow control?
• 10.3 The modem seems to always connect at a strange rate. When I use minicom, the modem will always use 14400. However, PPP is using 9600 or 7200 or even 2400. How do I fix this?
• 10.4 The ftp transfers seems to be very slow when I do a \get\ operation. The \put\ operation is much faster. Why?
• 10.5 The proxyarp function fails to find the hardware address.

11. Routing and other problems

• 11.1 My route to the remote keeps disappearing! It last for about 3 minutes and then the route just goes away. Help!
• 11.2 I would like to attach my other computers on my network to the Internet through my PPP connection. I have only the one IP address which is assigned to me from my service provider. (It may even have been dynamically assigned.) How may I do this?
• 11.3 I can reach the remote server, but I can not get anywhere else.
• 11.4 I have a default route and I still can't get anywhere else! Now what?
• 11.5 I can not ping my local IP address

12. Interactions with other PPP implementations

• 12.1 How do I connect to a Windows NT server?
• 12.2 I tried to use MSCHAP or PAP with Windows NT and it fails with "E=691". Now what?
• 12.3 How do I support Windows 95?
• 12.4 I am using a Trumpet (for MSDOS) and the connection simply terminates. Why is this happening?
• 12.5 I am using dp-3.1.2 (with SunOS) and the system will not allow me to use anything but ping, or nslookup. Why is this happening?
• 12.6 My provider wants to use a dynamic DNS address which is not the same with every connection. Yet, Linux wants just one address in the /etc/resolv.conf file. This works with Microsoft Windows 95, but how do I make it work with Linux?

13. Other messages written to the system log

• 13.1 Alarm
• 13.2 SIGHUP
• 13.3 SIGINT
• 13.4 Unknown protocol (c025) received!.
• 13.5 Unknown protocol (80fd) received!.
• 13.6 The connection fails with errors \ioctl(TIOCGETD): I/O error\ or \ioctl(PPPIOCSINPSIG): I/O error\. What now?
• 13.7 Sometimes the messages \ioctl(PPPIOCGDEBUG): I/O error\, \ioctl(TIOCSETD): I/O error\ and \ioctl(TIOCNXCL): I/O error\ occur. Why?
• 13.8 My ifconfig has strange output for PPP.
• 13.9 The file /proc/net/dev seems to be empty
• 13.10 The kernel reports that the PPP devices are being unlinked when the system is being started.
• 13.11 I just checked /proc/net/dev and there are no PPP devices. Where did they go?

14. Network routing issues (using PPP as a \cheap\ bridge)

• 14.1 Slattach and ifconfig don't work as they do with SLIP
• 14.2 I want the route to the network and not the route to the host.

15. Other features and protocols

• 15.1 What about support for \demand dial\
• 15.2 What about \filtering\
• 15.3 How about IPX?
• 15.4 How about NETBIOS?
• 15.5 I need ISDN support. Is there any?
• 15.6 I would like multi-point support. Is there any support?
• 15.7 How about just standard synchronous PPP?

16. Miscellaneous

• 16.1 Do you have a PPP compatible mail reader?
• 16.2 How about a news reader?

17. Questions about chat

• 17.1 My modem wont dial when I run chat
• 17.2 The modem dials only on every second attempt
• 17.3 The chat script stops after sending the account name and it never receives the password prompt.
• 17.4 The chat script stops before finishing and fails to make the connection
• 17.5 When I attempt to run chat, it says that the -l parameter is invalid. Why?
• 17.6 I ran chat. It seems to want to use the local terminal as the modem and it does not talk to the modem. How do I specify the modem name to chat?
• 17.7 When I run pppd and chat along with mgetty then the connection does not start. If I stop mgetty, then pppd will work. Why?