Howto:Which ports are used for PPTP connections?
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FAQ:
Which ports are used for PPTP connections?
Answer:
PPTP uses TCP connections to port 1723 for signalling and IP protocol "GRE" (General Routing Encapsulation) for traffic.
A common mistake in configuring firewalls for use with PPTP is to open port 1723 (allowing connections to be established) but fail to open protocol 47 (denying actual data from passing through the tunnel). Some operating systems include "PPTP ping" utiliies (pptpsrv and pptpclnt in Windows 2000) that verify both are opened.
PPTP uses TCP port 1723 to establish a connection. When opening holes in a firewall to support PPTP, one must be careful to not specify UDP port 1723 instead of TCP.
For more information regarding PPTP, see the links below.