[pptp-server] Criminal routing? - is pptp affected by split routing?

[G. Georgiev]

        Hello,

        After few days of debugging and finding a GRE patch for traceroute
in order to check why my pptp link does not work I need to understand
how a host on Internet may reply if I traceroute it trough a modem
interface and refuse to show up over my regular (cable) link. I am
able every time to ping vpn.galileo.com, but it does not create a pptp
link when I connect to Internet over the cable, however the link is
easily established if I forward it over my reserva line, a modem.

        Does someone have an idea why vpn.galileo.com replies to trace
route only over the modem link? I may ping it over cable, but not
traceroute or create the GRE tunnel needed for pptp to it. A normal
TCP connection (pptp control connection) establishes over the cable,
but the GRE tunnel fails to build. I did the traceroute with GRE packets
(thanks to Neale Banks for the patch), the result is same.

	May the problem be asymetric routing with my ISP? Is pptp affected
by split / asymetric/ any other perverse routing?

        George

	I shoud mention that the line worked fine for an year, but failed
three days ago and I can check nothing on the other end. They are good,
anyways, i make pptp link over the modem without problem.

	

Traceroute over cable - vpn.galileo.com can not be seen:

 1  10.48.160.1 (10.48.160.1)  9.067 ms  9.352 ms  11.871 ms
 2  modemcable090.241-200-24.mtl.mc.videotron.ca (24.200.241.90)  7.826 ms
 3  10.154.0.34 (10.154.0.34)  9.283 ms  8.997 ms  13.797 ms
 4  ia-cduc-bb02-ge3-0.videotron.net (207.96.163.9)  7.583 ms  8.673 ms
 5  if-7-3.core2.Montreal.Teleglobe.net (207.45.204.41)  15.974 ms  45.709
 6  if-0-0.core3.NewYork.Teleglobe.net (207.45.222.109)  27.011 ms  16.043
 7  if-7-0.core1.NewYork.Teleglobe.net (64.86.83.153)  16.3 ms  15.736 ms
 8  if-10-0.bb8.NewYork.Teleglobe.net (207.45.223.110)  18.568 ms  17.027
 9  ix-8-0-1.bb8.NewYork.Teleglobe.net (207.45.198.74)  17.617 ms  16.507
10  0.at-6-1-0.XL1.NYC9.ALTER.NET (152.63.22.226)  18.285 ms  25.157 ms
11  0.so-7-0-0.XR1.NYC9.ALTER.NET (152.63.23.138)  15.994 ms  17.456 ms
12  0.so-4-0-0.TR1.NYC9.ALTER.NET (152.63.15.110)  15.612 ms  15.739 ms
13  125.at-5-0-0.TR1.SLT4.ALTER.NET (152.63.6.46)  67.144 ms  67.931 ms
14  191.at-1-0-0.XR1.SLT4.ALTER.NET (152.63.89.17)  68.591 ms  76.323 ms
15  187.ATM7-0.GW4.SLT4.ALTER.NET (152.63.91.245)  68.219 ms  68.373 ms
16  galileo-gw1.customer.alter.net (157.130.169.202)  81.995 ms  105.072
17  * * *
18  * * *
19  * * *
20  * * *
21  * * *
22  * * *
23  * * *
24  * * *
25  * * *
26  * * *
27  * * *
28  * * *
29  * * *
30  * * *

Traceroute over the modem - vpn.galileo.com is visible:
 1  ppp005.111-253-207.mtl.mt.videotron.ca (207.253.111.5)  136.904 ms
 2  ia-piex-gw02-fe5-1-0.videotron.net (207.96.135.1)  139.473 ms  127.66
 3  ia-piex-bb02-ge2-0.videotron.net (207.253.253.132)  299.83 ms  357.658
 4  sl-gw32-chi-4-0.sprintlink.net (160.81.231.1)  129.905 ms  176.286 ms
 5  sl-bb20-chi-4-0.sprintlink.net (144.232.26.13)  159.81 ms  137.514 ms
 6  sl-bb22-chi-14-0.sprintlink.net (144.232.26.6)  199.835 ms  197.53 ms
 7  ATM1-0.BR1.CHI2.ALTER.NET (204.255.168.241)  169.804 ms  157.631 ms
 8  0.so-5-0-0.XL1.CHI2.ALTER.NET (152.63.64.114)  150.004 ms  137.49 ms
 9  0.so-7-0-0.XR1.CHI2.ALTER.NET (152.63.67.130)  149.749 ms  177.696 ms
10  0.so-3-0-0.TR1.CHI2.ALTER.NET (152.63.15.86)  159.828 ms  147.676 ms
11  126.at-5-1-0.TR1.SLT4.ALTER.NET (152.63.1.74)  189.83 ms  217.681 ms
12  191.at-1-0-0.XR1.SLT4.ALTER.NET (152.63.89.17)  199.829 ms  187.676 ms
13  187.ATM7-0.GW4.SLT4.ALTER.NET (152.63.91.245)  179.822 ms  187.669 ms
14  galileo-gw1.customer.alter.net (157.130.169.202)  189.829 ms  197.647
15  * * *
16  vpn.galileo.com (12.17.202.16)  290.005 ms * *