[pptp-server] ADSL line pptp client not connecting.

[awilliam at whitemice.org]

>>>>>yesterday a dedicated ADSL line and when I try to
>>>>>establish the pptp connection over this ADSL line
>>>>>there is just no response from the
>>>[...]
>>>-> Yep.  They installed my ADSL line today, and PPTP
>>>-> stopped working.  It does connect and start but then
>>>-> the whole thing dies (ppp has a read error)
>>>   Could it be that your ISPs are doing some packet-filtering?
>>> Is there *anyone* who was used PoPToP over an ADSL connection
>>> successfully?  It would be good to know that it _can_ work...
>> Steve Cowles and I have tested PoPToP over ADSL successfully.
>One of my customers (a lawyers office in downtown Dallas) wanted me 
to
>implement a PPTP solution using their existing Linux based firewall 
so that
>they could connect into the office from their homes. Piece of cake, 
so I
>thought... considering the work Tom and I have done in setting up our 
own
>PopTop servers on linux.
>To make this long and frustrating implementation story short, I was 
NOT able
>to implement PPTP at their office due to the fact that the ISP was 
blocking
>"syn" type packets at their routers. When I contacted the ISP, they 
told me
>that my customer would have to sign-up for their "business" type of 
service.
>The business service did not block (filter) "syn" packets <groan>. 
Needless
>to say, my customer was not willing to pay the 3x price differential 
to
>switch service types. They decided to wait until their current 
contract
>expired with the ISP and then switch.

What would be symtomatic of SYN filtering.  These are the messages the 
PPTP server (I am the client on ADSL):

Jul  1 17:34:30 firewall pppd[29515]: pppd 2.3.10 started by root, uid 
0
Jul  1 17:34:30 firewall pppd[29515]: Using interface ppp0
Jul  1 17:34:30 firewall pppd[29515]: Connect: ppp0 <--> /dev/pts/2
Jul  1 17:34:30 firewall pppd[29515]: LDAP Routine done.
Jul  1 17:34:30 firewall pppd[29515]: LDAP Routine done.
Jul  1 17:35:00 firewall pptpd[29514]: GRE: 
read(fd=4,buffer=804d7e0,len=8196) from PTY failed: status = -1 error 
= Input/output error
Jul  1 17:35:00 firewall pptpd[29514]: CTRL: PTY read or GRE write 
failed (pty,gre)=(4,5)
Jul  1 17:35:00 firewall pptpd[29514]: CTRL: Client 64.31.14.182 
control connection finished
Jul  1 17:35:00 firewall pptpd[29514]: CTRL: Exiting now
Jul  1 17:35:00 firewall pptpd[17083]: MGR: Reaped child 29514
Jul  1 17:35:00 firewall pppd[29515]: LCP: timeout sending 
Config-Requests 
Jul  1 17:35:00 firewall pppd[29515]: Connection terminated.
Jul  1 17:35:00 firewall pppd[29515]: Exit.