Seeing as everybody seems to be making contributions along the lines of
"no, that's not the problem, it's really...", here's what my copy of the
PPP-HOWTO has to say on the subject of "Serial line is not 8 bit clean":
*** Start of extract ***
18.3. The syslog says "serial line is not 8 bit clean..."
There are variations on this too - such as serial line looped back
etc., and the cause can be one (or a sequence) of a number of things.
To understand what is going on here, it is necessary to grasp a bit of
what is going on behind the scenes in pppd itself.
When pppd starts up, it sends LCP (link control protocol) packets to
the remote machine. If it receives a valid response it then goes on to
the next stage (using IPCP - IP control protocol packets) and only
when this negotiation completes is the actual IP layer started so that
you can use the PPP link.
If there is no ppp server operating at the remote end when your PC
sends lcp packets, these get reflected by the login process at the far
end. As these packets use 8 bits, reflecting them strips the 8th bit
(remember, ASCII is a 7 bit code). PPP sees this and complains
accordingly.
There are several reasons this reflection can occur.
18.3.1. You are not correctly logging into the server
When your chat script completes, pppd starts on your PC. However, if
you have not completed the log in process to the server (including
sending any command required to start PPP on the server), PPP will
not start.
So, the lcp packets are reflected and you receive this error.
You need to carefully check and correct (if necessary) your chat
script (see above).
18.3.2. You are not starting PPP on the server
Some PPP servers require you to enter a command and/or a RETURN after
completing the log in process before the remote end starts ppp.
Check your chat script (see above).
If you log in manually and find you need to send a RETURN after this
to start PPP, simply add a blank expect/send pair to the end of your
chat script (an empty send string actually sends a RETURN).
18.3.3. The remote PPP process is slow to start
This one is a bit tricksy!
By default, your Linux pppd is compiled to send a maximum of 10 lcp
configuration requests. If the server is a bit slow to start up, all
10 such requests can be sent before the remote PPP is ready to receive
them.
On your machine, pppd sees all 10 requests reflected back (with the
8th bit stripped) and exits.
There are two ways round this:-
Add lcp-max-configure 30 to your ppp options. This increases the
maximum number of lcp configure packets pppd sends before giving up.
For really slow server, you may need even more than this.
Alternatively, you can get a bit tricksy in return. You may have
noticed that when you logged in by hand to the PPP server and PPP
started there, the first character of the ppp garbage that appears was
always the tilde character (~).
Using this knowledge we can add a new expect/send pair to the end of
the chat script which expects a tilde and sends nothing. This would
look like:-
______________________________________________________________________
\~ ''
______________________________________________________________________
Note: as the tilde character has a special meaning in the shell, it
must be escaped (and hence the leading backslash).
*** End of Extract ***
Hope this helps :-)
On Mon, 21 Feb 2000, Will Merkens wrote:
> Andrew Post wrote:
> >
> > This problem aporadically occurs with my Mandrake 6.1 setup as well. It
> > hasn't happened in several months, and I haven't changed anything
> > related to PPP between then and now. I never figured out what caused the
> > problem. I'm wondering if it's a problem with some ISPs' setup that
> > Win9x and WinNT work around and Linux doesn't. Maybe you should contact
> > the maintainer of PPP with a description of the problem.
> >
> > Andrew
> >
> > Ramon Gandia wrote:
> > >
> > > Jean-Michel Dault wrote:
> > > >
> > > > The log said your line is not 8-bit clean. That probably means your modem
> > > > speed is not set correctly. Try with 19200, 38400 and 115200 to see if it
> > > > changes something.
> > >
> > > Common enough assumption. It means nothing of the sort. It
> > > simply means the pppd deamon did not start. The error message
> > > is misleading. This is a "well known behaviour."
> > >
> > > In his case, the modems had already negotiated and passed
> > > some data back and forth. So its not a serial port problem,
> > > its a protocol problem.
>
>
> It's not speed and it's not that pppd did not start.
>
> LCP is the system where client and server sides negated what ppp
> features are to be used in that particular connection.
>
> If you turn up the debug you will see it negotiating things like
> comress/chap/pap etc, the problem here (and I have not seen this for
> years) is that neither end wants to become the master, so each side is
> expecting the other side to set the terms of the negotiation. result is
> a LCP time-out.
>
> I think I solved this a long time ago by forcing a CHAP negation.
>
> I see this effect from win9x ppp connections sometimes too.
>
> I haven't seen it from a ISP in a long time.
--
Phil Edwards
Technical Specialist
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