[Comm] pptp vs routing

[Alexander Vasiliev]

On Tue, Nov 04, 2003 at 07:52:28AM +0600, Seirge P. Kondratyev wrote:
> >>Kernel IP routing table
> >>Destination     Gateway         Genmask         Flags Metric Ref    Use 
> >>Iface
> >>tun-gw.tomline. *               255.255.255.255 UH    0      0        0 
> >>ppp0
> >>^^^^^^^^^^^^^^^							 ^^^^
> >>Как видно, default остается тем же, а вот все портящая запись появляется 
> >>первой... это роутинг ма машину, предоставляющую vpn...
> >>Помогите, или хотя бы объясните зачем она и почему без неё все работает...
> >>
> >>   
> >
> Мда... Но если эту запись удалить, работоспособность восстанавливается, 
> ведь как я понимаю, из-за этой записи он обращается к tun-gw.tomline.ru 
> через ppp0, который работает через tun-gw.tomline.ru(это сам сервер vpn), 
> который обращается к tun-gw.tomline.ru через ppp0, через который... Вот он 
> этот ip loop. а в 
> file:///usr/share/doc/pptp-client-1.1.0/howto-diagnosis.html#ip_loop
> предлагают просто разобраться, где он появляется, что я и не понимаю...
> 
> seirge
Похоже в Вашем случае нужно см п. 3 (ниже...)

28. LCP EchoReq without LCP EchoRep                                                                                              

Symptom:
connection is established but no data transfer happens, ifconfig shows
large amounts of data transmitted on PPTP tunnel, tcpdump shows many
transmitted packets, the connection is closed after one minute, and logs
contain this sequence:                                                                                  

rcvd [LCP EchoReq id=0x1                                                                                                       
sent [LCP EchoRep id=0x1                                                                                                       
sent [LCP EchoReq id=0x1                                                                                                       
rcvd [LCP EchoReq id=0x2                                                                                                       
sent [LCP EchoRep id=0x2                                                                                                       
sent [LCP EchoReq id=0x2                                                                                                       

which indicates that echo requests from the server are being received                                                        
by the client, which issues an echo reply, but that echo requests from                                                       
the client are not generating echo replies from the server.

Diagnosis:
the route to the PPTP Server has changed to include the tunnel itself,
and packets are being looped.  Packets sent through the VPN are being
encapsulated in PPP over GRE, and then sent through the same interface
again.                                                                                                        

See our diagram showing this situation.                                                                                      

Solution:
Examine the routing table using netstat -rn before and after the
tunnel becomes active.  Determine why the route to the PPTP Server                                                        
is via the tunnel interface.  The reasons may be:                                                                             

1.  the defaultroute option was used,                                                                                       

2.  distribution specific or local interface-up scripts changed
the route, or                                                                                                               

3.  the PPTP Server may have given its own IP address for the new                                                           
interface.                                                                                                              

If defaultroute is in the options given to pppd remove it, and
use other means to provide routes through the tunnel interface.                                                                  

If scripts are adding or changing routes, fix them.                                                                          

If the PPTP Server is providing an incorrect IP address, force
a more appropriate address by adding an option such as :10.0.1.1,
where 10.0.1.1 is the address to be adopted.  It would be better
to fix the PPTP Server.                                                                                                                 
--
Александр Васильев
ЗАО "Таском"
vav на tascom.ru