CompTIA Security Plus Mock Test Q131

A company has implemented PPTP as a VPN solution. Which of the following ports would need to be opened on the firewall in order for this VPN to function properly? (Select TWO).

A. UDP 1723
B. TCP 500
C. TCP 1723
D. UDP 47
E. TCP 47

Correct Answer: C,D
Section: Network Security

Explanation:
A PPTP tunnel is instantiated by communication to the peer on TCP port 1723. This TCP connection is then used to initiate and manage a second GRE tunnel to the same peer. The PPTP GRE packet format is non-standard, including an additional acknowledgement field replacing the typical routing field in the GRE header. However, as in a normal GRE connection, those modified GRE packets are directly encapsulated into IP packets, and seen as IP protocol number 47.

Incorrect Answers:
A, E: PPTP uses a control channel over TCP and a GRE tunnel operating to encapsulate PPP packets.
B: TCP port 500 is used by the Internet Security Association and Key Management Protocol (ISAKMP)

References:
http://en.wikipedia.org/wiki/Point-to-Point_Tunneling_Protocol
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers