ISAKMP (VPN) uses which port? (alternative item)

ISAKMP (VPN) uses which port? (alternative item)

• A. 4500
• B. 1701
• C. 1194
• D. 500

Answer: (D)

ISAKMP is the protocol used to negotiate and establish the security associations for IPsec, so its negotiation messages flow over UDP port 500 by default. That makes port 500 the standard choice for ISAKMP/IKE. In environments with NAT, NAT traversal often uses UDP port 4500 to carry IPsec traffic, but the initial ISAKMP negotiations still occur on port 500. The other ports correspond to different VPN services—1701 is for L2TP, and 1194 is commonly used by OpenVPN—so they aren’t the default ISAKMP port.

ISAKMP is the protocol used to negotiate and establish the security associations for IPsec, so its negotiation messages flow over UDP port 500 by default. That makes port 500 the standard choice for ISAKMP/IKE. In environments with NAT, NAT traversal often uses UDP port 4500 to carry IPsec traffic, but the initial ISAKMP negotiations still occur on port 500. The other ports correspond to different VPN services—1701 is for L2TP, and 1194 is commonly used by OpenVPN—so they aren’t the default ISAKMP port.