Connection falls with pptp client

[Ibon Castilla Varela-2]

Hi there:

First I describe the scenario:
 - Ubuntu Dapper 6.06.2 Server
 - pptp-linux package 1.7.0-1ubuntu1 (pptp 1.7.0 version)
 - Cable modem Internet connection.

This is what happens:
 I use Internet connection to establish an VPN connection to obtain an static IP from my ISP (Euskaltel at Spain),
using pptp. The VPN works well, but sometimes (seems random to me) the connection falls down and this is what
syslog tell me: "pppd[pid-number]: Couldn't get channel number: Input/output error", when I try to connect again.
After a reboot it connects again.
 I try to debug the process, and I realized that a lot of messages like "buffering packet X (expecting Y, lost or
reordered)", but reading the FAQ I found that this behavior can be normal.

The question:
 How could I debug this situation to find why the connection is falling down?. Could it be related to physical
interfaces MTUs?.

Ibon.

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[James Cameron-2]

On Thu, Apr 02, 2009 at 03:26:44PM +0200, Ibon Castilla wrote:
> First I describe the scenario:
>  - Ubuntu Dapper 6.06.2 Server

Old.

>  - pptp-linux package 1.7.0-1ubuntu1 (pptp 1.7.0 version)

Old.  Current is 1.7.2.

You should really be posting to the pptp client mailing list.
http://pptpclient.sourceforge.net/contact.phtml ... but as I'm on both,
I'll answer here as well.

>  - Cable modem Internet connection.

Should not be relevant.

> This is what happens:
>  I use Internet connection [...]

I presume that is some program provided by Ubuntu on that system?  Has
it got a different name, or package source?

> [...] to establish an VPN connection to obtain an static IP from my
> ISP (Euskaltel at Spain), using pptp. The VPN works well, but
> sometimes (seems random to me) the connection falls down [...]

You should diagnose why the connection terminates.  For that you should
gather debug log from pppd.
http://pptpclient.sourceforge.net/howto-diagnosis.phtml#debug
Analyse the debug log at the point of disconnection.

This is potentially a separate problem to trying to reconnect
immediately afterward.

> and this is what syslog tell me: "pppd[pid-number]: Couldn't get
> channel number: Input/output error", when I try to connect again.

"Input/output error" is EIO.

May be related to Debian Bug #427586 for which I shipped a fix in pptp
1.7.2, please upgrade to that version and try again.

May be related to how your "Internet connection" software uses pptp, try
manually initiating a call.  See
http://pptpclient.sourceforge.net/howto-ubuntu.phtml#configure_by_hand
for the "Configuration, by hand" section.

The error comes from pppd/sys-linux.c, in the function
generic_establish_ppp, which converts a file descriptor into a ppp
interface.

Try checking for bugs in the ppp package version you are using.

The first thing the function does is to issue a PPPIOCGCHAN ioctl
against the file descriptor.  This is handled by the kernel module
ppp_async, in source file drivers/net/ppp_async.c ... not knowing your
kernel version I cannot see exactly what might cause EIO.

Wild guess ... pptp is exiting very quickly after pppd starts it, as a
result the file descriptor refers to a pseudo terminal that is not
available.  Examine a combined pptp and pppd debug log carefully.

> After a reboot it connects again.

Good.

> I try to debug the process, and I realized that a lot of messages
> like "buffering packet X (expecting Y, lost or reordered)", but
> reading the FAQ I found that this behavior can be normal.

Yes, that is normal.  You appear to have captured pptp debug data, but
since the error is with pppd it is more logical to capture pppd debug
data as well.

> The question:
> How could I debug this situation to find why the connection is falling down?.

Respond to suggestions above.

> Could it be related to physical interfaces MTUs?.

No, I don't think so.

--
James Cameron                         http://quozl.netrek.org/
HP Open Source, Volunteer             http://opensource.hp.com/
PPTP Client Project, Release Engineer http://pptpclient.sourceforge.net/

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