What are the ports used in the Virtual Private Network (VPN)

Internet Protocol Security (IPSec) uses IP protocol 50 for Encapsulated Security Protocol (ESP), IP protocol 51 for Authentication Header (AH) .IPSEC uses UDP port 500 for IKE Phase 1 negotiation and Phase 2 negotiations. UDP ports 500 and 4500 are used, if NAT-T is used for IKE Phase 1 negotiation and Phase 2 negotiations

Secure Sockets Layer (SSL) uses TCP port 443, it works by using a private key to encrypt data that is transferred over the SSL connection. SSL also uses 465 Secure SMTP, 993 Secure IMAP, and 995 Secure POP.

Layer Two Tunneling Protocol (L2TP) uses TCP port 1701 and is an extension of the Point-to-Point Tunneling Protocol (PPTP). L2TP is often used with IPSec to establish a Virtual Private Network.