VPN using ssh & pppd - getting Resource temporarily unavailable

Wayne Johnson

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Feb 28, 2001, 12:07:36 AM2/28/01

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I'm attempting to set up a VPN using PPP over SSH on 2 linux systems
using the new pppd pty option.

I'm using ppp-2.3.11-4 and SSH Version 1.2.30.

It works great most of the time, at least till I try doing an ftp
transfer or replicate a notes database. When I do that the connection
drops and I get the error:

Jan 26 11:57:39 nexus pppd[21326]: Error writing standard output:
Resource temporarily unavailable
Jan 26 11:57:39 nexus pppd[21325]: Modem hangup
Jan 26 11:57:39 nexus pppd[21325]: Connection terminated.
Jan 26 11:57:39 nexus pppd[21325]: Connect time 0.6 minutes.
Jan 26 11:57:39 nexus pppd[21325]: Sent 8540 bytes, received 4145 bytes.

Jan 26 11:57:39 nexus pppd[21325]: Exit.
Jan 26 11:57:41 nexus sshd[21323]: log: Closing connection to
204.217.194.246

I thought it might have something to do with the contents of what I was
sending (like a ssh escape character), but it is somewhat sporadic, only
failing 80% of the time using the same data. I even tried to send pings
with -p set to every combination from 0000 to ffff. That doesn't seem
to cause the error.

I've tried setting the pppd escape option to make sure I'm not sending
the ssh escape character, as well as setting ssh -e none. This didn't
help

My peers file contains:
pty "ssh dccmn.com -e none -l tunnel '/usr/sbin/pppd notty call candle'"

escape 7e
noauth
192.169.0.2:192.169.0.1

and the remote peers file contains:
noauth
notty
passive
ipparam candle
escape 7e

I now guessing that somehow pppd is sending a packet that is too large
for ssh's shell to process.

Am I missing something? Anyone have any suggestions on what to do
next? It there a better way to set up a VPN running on a client/server
protocol. By this I mean, initiating the VPN connection from one side
only?

TIA,

James Carlson

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Mar 1, 2001, 6:56:44 AM3/1/01

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Wayne Johnson <wd...@yahoo.com> writes:
> Jan 26 11:57:39 nexus pppd[21326]: Error writing standard output:
> Resource temporarily unavailable

This is a well-known bug in pppd. The char shunt code in older
versions of pppd/main.c didn't properly handle EAGAIN. Upgrade to
ppp-2.4.0 and this should go away.

(If you want to stay with 2.3.11 for some reason, you'll need to patch
charshunt() so that when write() fails with EAGAIN, it loops around
again rather than exiting.)

> escape 7e

There's no need to do that. 7E is always escaped.

--
James Carlson <car...@workingcode.com>
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp

Wayne Johnson

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Mar 2, 2001, 9:25:23 PM3/2/01

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Great, thanks, I'll try that.

Wayne Johnson

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Mar 2, 2001, 9:55:36 PM3/2/01

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Any idea where I can get a 2.4 RPM, or the eagain patch. Unfortunately
Redhat doesn't have it yet. I tried the 2.4 source RPM from RedHat but
can't seem to unpack it.

Thanks.

Bill Unruh

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Mar 2, 2001, 11:38:01 PM3/2/01

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In <3AA05D27...@yahoo.com> Wayne Johnson <wd...@yahoo.com> writes:

>Any idea where I can get a 2.4 RPM, or the eagain patch. Unfortunately
>Redhat doesn't have it yet. I tried the 2.4 source RPM from RedHat but
>can't seem to unpack it.

rpm -Uhv ppp2.4.0.src.rpm
(or whatever the name of the source rpm is.)

cd /usr/src/RPM/SOURCES
rpm -ba ../SPECS/ppp*
cd ../RPMS/i686
and there is an rpm to install.

>Thanks.