Arch Linux

Mr.Cat

Member

Registered: 2008-09-27

Posts: 79

"Modem hangup" on pptp

When I connect to a corporate pptp vpn via internet and start using rdesktop - the vpn connection terminates in a couple of minutes:

Aug 23 19:15:42 cat-arch pppd[4650]: Modem hangup
Aug 23 19:15:42 cat-arch pppd[4650]: Connect time 12.9 minutes.

I've noticed that when using rdesktop the following lines appear in /var/log/daemon.log:

Aug 23 19:15:42 cat-arch pptp[4657]: anon log[decaps_gre:pptp_gre.c:414]: buffering packet 1981 (expecting 1978, lost or reordered)

When accessing http and smd resources those lines also appear, but not so frequently and the connection does not terminate.

Pppd is configured as follows:

pppd options in effect:
debug        # (from command line)
nodetach        # (from command line)
logfd 2        # (from command line)
dump        # (from command line)
noauth        # (from /etc/ppp/peers/peer)
refuse-eap        # (from /etc/ppp/peers/peer), my comment: required for successful authentication
name DOMAIN\\Name        # (from /etc/ppp/peers/peer)
remotename peer        # (from /etc/ppp/peers/peer)
        # (from /etc/ppp/peers/peer)
pty pptp x.x.x.x --nolaunchpppd        # (from /etc/ppp/peers/peer)
crtscts        # (from /etc/ppp/options)
        # (from /etc/ppp/options)
asyncmap 0        # (from /etc/ppp/options)
lcp-echo-failure 4        # (from /etc/ppp/options)
lcp-echo-interval 30        # (from /etc/ppp/options)
hide-password        # (from /etc/ppp/options)
ipparam xxx        # (from /etc/ppp/peers/peer)
proxyarp        # (from /etc/ppp/options)
usepeerdns        # (from /etc/ppp/peers/peer)
nobsdcomp        # (from /etc/ppp/peers/peer)
nodeflate        # (from /etc/ppp/peers/peer)
require-mppe        # (from /etc/ppp/peers/peer), my comment: required for successful authentication
noipx        # (from /etc/ppp/options)

My internet connection is 3Mbit via dlink dir-320 router and l2tp vpn. And mstsc under windows works fine.
When I connect to the corporate network via the same vpn gate but at a different location (the same ISP, the same l2tp vpn, dlink dir-615 router, 10Mbit channel) everything works fine under both windows and linux.

What am I doing wrong?

Last edited by Mr.Cat (2010-01-31 09:24:39)

monsieur-paul

Member

Registered: 2011-03-15

Posts: 1

Re: "Modem hangup" on pptp

I had a similar issue. Fortunately, I had two different ways to connect, where one (network-manager) was working fine, and the other one (pon) showed this problem. So I could compare all relevant settings...

I discovered, the message '...buffering packet 1981 (expecting 1978, lost or reordered)' is no problem, and happens on stable connenctions as well.

The real problem started with this line in /var/log/daemon.log:

Mar 15 11:13:11 XXXX pptp[6438]: anon warn[decaps_gre:pptp_gre.c:331]: short read (-1): Message too long

I realized, the problem was due to a too large MTU size for ppp0 (was 1456). I changed it to 1400, and everything was fine.

# ifconfig ppp0 mtu 1400

Last edited by monsieur-paul (2011-03-15 11:16:17)