PPTP with NAT

jresendizz — Fri, 21 Feb 2020 08:30:39 GMT

Hi everyone!

One of my costumers is connected to my Internet network (im an isp), the costumer is using dynamic nat, and on the other end, there is a PPTP server (on a hosted environment), the costumer complains that sometimes can´t connect throught the pptp tunnel, but i always see the TCP port 173, and after that, the GRE session..but the problem is that the costumer can´t make it works..

As an example, this is a snapshot of the nat translation:

ADVERTISING#sh ip nat translations | i 148.244.244

tcp <IP_ADDRESS_OUTSIDE>:1329 192.168.1.132:1329 <PPTP_IP_ADDRESS>:3389 <PPTP_IP_ADDRESS>:3389

gre <IP_ADDRESS_OUTSIDE>:57 192.168.1.133:256 <PPTP_IP_ADDRESS>:256 <PPTP_IP_ADDRESS>:57

tcp <IP_ADDRESS_OUTSIDE>:1026 192.168.1.133:1049 <PPTP_IP_ADDRESS>:1723 <PPTP_IP_ADDRESS>:1723

gre <IP_ADDRESS_OUTSIDE>:50145 192.168.1.133:50145 <PPTP_IP_ADDRESS>:50145 <PPTP_IP_ADDRESS>:50145

gre <IP_ADDRESS_OUTSIDE>:23 192.168.1.134:256 <PPTP_IP_ADDRESS>:256 <PPTP_IP_ADDRESS>:23

tcp <IP_ADDRESS_OUTSIDE>:1114 192.168.1.134:1114 <PPTP_IP_ADDRESS>:1723 <PPTP_IP_ADDRESS>:1723

gre <IP_ADDRESS_OUTSIDE>:17376 192.168.1.134:17376 <PPTP_IP_ADDRESS>:17376 <PPTP_IP_ADDRESS>:17376

tcp <IP_ADDRESS_OUTSIDE>:1025 192.168.1.135:1077 <PPTP_IP_ADDRESS>:3389 <PPTP_IP_ADDRESS>:3389

tcp <IP_ADDRESS_OUTSIDE>:1054 192.168.1.138:1036 <PPTP_IP_ADDRESS>:3389 <PPTP_IP_ADDRESS>:3389

gre <IP_ADDRESS_OUTSIDE>:2 192.168.1.139:256 <PPTP_IP_ADDRESS>:256 <PPTP_IP_ADDRESS>:2

gre <IP_ADDRESS_OUTSIDE>:994 192.168.1.139:994 <PPTP_IP_ADDRESS>:994 <PPTP_IP_ADDRESS>:994

tcp <IP_ADDRESS_OUTSIDE>:1036 192.168.1.139:1052 <PPTP_IP_ADDRESS>:3389 <PPTP_IP_ADDRESS>:3389

tcp <IP_ADDRESS_OUTSIDE>:1268 192.168.1.139:1268 <PPTP_IP_ADDRESS>:1723 <PPTP_IP_ADDRESS>:1723

gre <IP_ADDRESS_OUTSIDE>:9 192.168.1.143:256 <PPTP_IP_ADDRESS>:256 <PPTP_IP_ADDRESS>:9

As you can see, there is NAT on the CPE in order to change the 192.168.1.x IP to a public ip address (source to the PPTP Server), on the server side, there is another NAT in order to have a public ip address <PPTP_IP_ADDRESS>..

This is the debug attached..

Does anyone have an idea what can be happening??im new about pptp...thank you very much in advice!

Alfonso

topic PPTP with NAT in Network Security

PPTP with NAT