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simple isdn4linux PPP FAQ .. to be continued .. not 'debugged'

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Q01: what's pppd,ipppd, syncPPP , asyncPPP ??

Q02: error message "this systems lacks PPP support"

Q03: strange information using 'ifconfig'

Q04: MPPP?? What's that and how can I use it ...

Q05: I tried MPPP but it doesn't work

Q06: can I use asynchronous PPP encapsulation with network devices

Q07: A SunISDN machine can't connect to my i4l system

Q08: I wanna talk to several machines, which need different configs

Q09: Starting the ipppd, I get only error messages from i4l

Q10: I wanna use dynamic IP address assignment

Q11: I can't connect. How can I check where the problem is.

Q12: How can I reduce login delay?

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Q01: pppd,ipppd, syncPPP , asyncPPP .. what is that ?

   what should I use?

A: The pppd is for asynchronous PPP .. asynchronous means

   here, the framing is character based. (e.g when

   using ttyI* or tty* devices)

   The ipppd handles PPP packets coming in HDLC

   frames (bit based protocol) ... The PPP driver

   in isdn4linux pushes all IP packets direct

   to the network layer and all PPP protocol

   frames to the /dev/ippp* device.

   So, the ipppd is a simple external network

   protocol handler.

   If you login into a remote machine using the

   /dev/ttyI* devices and then enable PPP on the

   remote terminal server -> use the 'old' pppd

   If your remote side immediately starts to send

   frames ... you probably connect to a

   syncPPP machine .. use the network device part

   of isdn4linux with the 'syncppp' encapsulation

   and make sure, that the ipppd is running and

   connected to at least one /dev/ippp*. Check the

   isdn4linux manual on how to configure a network device.

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Q02: when I start the ipppd .. I only get the

   error message "this systems lacks PPP support"

A: check that at least the device 'ippp0' exists.

   (you can check this e.g with the program 'ifconfig')

   The ipppd NEEDS this device under THIS name ..

   If this device doesn't exists, use:

        isdnctrl addif ippp0

        isdnctrl encap ippp0 syncppp

        ... (see isdn4linux doc for more) ...

A: Maybe you have compiled the ipppd with another

   kernel source tree than the kernel you currently

   run ...

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Q03: when I list the netdevices with ifconfig I see, that

   my ISDN interface has a HWaddr and IRQ=0 and Base

   address = 0

A: The device is a fake ethernet device .. ignore IRQ and baseaddr

   You need the HWaddr only for ethernet encapsulation.

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Q04: MPPP?? What's that and how can I use it ...

A: MPPP or MP or MPP (Warning: MP is also an

   acronym for 'Multi Processor') stands for

   Multi Point to Point and means bundling

   of several channels to one logical stream.

   To enable MPPP negotiation you must call the

   ipppd with the '+mp' option.

   You must also configure a slave device for

   every additional channel. (see the i4l manual

   for more)

   To use channel bundling you must first activate

   the 'master' or initial call. Now you can add

   the slave channels with the command:

       isdnctrl addlink 

   e.g:

       isdnctrl addlink ippp0

   This is different from other encapsulations of

   isdn4linux! With syncPPP, there is no automatic

   activation of slave devices.

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Q05: I tried MPPP but it doesn't work .. the ipppd

   writes in the debug log something like:

   .. rcvd [0][proto=0x3d] c0 00 00 00 80 fd 01 01 00 0a ...

   .. sent [0][LCP ProtRej id=0x2 00 3d c0 00 00 00 80 fd 01 ...

A: you forgot to compile MPPP/RFC1717 support into the

   ISDN Subsystem. Recompile with this option enabled.

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Q06: can I use asynchronous PPP encapsulation

   over the network interface of isdn4linux ..

A: No .. that's not possible .. Use the standard

   PPP package over the /dev/ttyI* devices. You

   must not use the ipppd for this.

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Q07: A SunISDN machine tries to connect my i4l system,

   which doesn't work.

   Checking the debug log I just saw garbage like:

!![ ... fill in the line ... ]!!

A: The Sun tries to talk asynchronous PPP ... i4l

   can't understand this ... try to use the ttyI*

   devices with the standard PPP/pppd package

A: (from Alexanter Strauss: )

!![ ... fill in mail ]!!

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Q08: A wanna talk to remote machines, which need

   a different configuration. The only way

   I found to do this is to kill the ipppd and

   start a new one with another config to connect

   to the second machine.

A: you must bind a network interface explicitly to

   an ippp device, where you can connect a (for this

   interface) individually configured ipppd.

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Q09: When I start the ipppd I only get error messages

   from the i4l driver ..

A: When starting, the ipppd calls functions which may

   trigger a network packet. (e.g gethostbyname()).

   Without the ipppd (at this moment, it is not

   fully started) we can't handle this network request.

   Try to configure hostnames necessary for the ipppd

   in your local /etc/hosts file or in a way, that

   your system can resolve it without using an

   isdn/ippp network-interface.

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Q10: I wanna use dynamic IP address assignment ... How

   must I configure the network device.

A: At least you must have a routing, which forwards

   a packet to the ippp network-interface to trigger

   the dial-on-demand.

   A default routing to the ippp-interface will work.

   Now you must choose a dummy IP address for your

   interface.

   If for some reason you can't set the default

   routing to the ippp interface, you may take any

   address of the subnet from which you expect your

   dynamic IP number and set a 'network route' for

   this subnet to the ippp interface.

   To allow overriding of the dummy address you

   must call the ipppd with the 'ipcp-accept-local' option.

A: You must know, how the ipppd gets the addresses it wanna

   configure. If you don't give any option, the ipppd

   tries to negotiate the local host address!

   With the option 'noipdefault' it requests an address

   from the remote machine. With 'useifip' it gets the

   addresses from the net interface. Or you set the address

   on the option line with the  option.

   Note: the IP address of the remote machine must be configured

   locally or the remote machine must send it in an IPCP request.

   If your side doesn't know the IP address after negotiation, it

   closes the connection!

   You must allow overriding of address with the 'ipcp-accept-*'

   options, if you have set your own or the remote address

   explicitly.

A: Maybe you try these options .. e.g:

    /sbin/ipppd :$REMOTE noipdefault /dev/ippp0

   where REMOTE must be the address of the remote machine (the

   machine, which gives you your address)

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Q11: I can't connect. How can I check where the problem is.

A: A good help log is the debug output from the ipppd...

   Check whether you can find there:

   - only a few LCP-conf-req SENT messages (less then 10)

     and then a Term-REQ:

     -> check whether your ISDN card is well configured

        it seems, that your machine doesn't dial

        (IRQ,IO,Proto, etc problems)

        Configure your ISDN card to print debug messages and

        check the /dev/isdnctrl output next time. There

        you can see, whether there is activity on the card/line.

   - there are at least a few RECV messages in the log:

     -> fine: your card is dialing and your remote machine

        tries to talk with you. Maybe only a missing

        authentication. Check your ipppd configuration again.

   - the ipppd exits for some reason:

     -> not good ... check /var/adm/syslog and /var/adm/daemon.

        Could be a bug in the ipppd.

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Q12: How can I reduce login delay?

A: Log a login session ('debug' log) and check which options

  your remote side rejects. Next time configure your ipppd

  to not negotiate these options. Another 'side effect' is, that

  this increases redundancy. (e.g your remote side is buggy and

  rejects options in a wrong way).