Which port is used by ISAKMP (VPN)?

Which port is used by ISAKMP (VPN)?

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

Answer: (B)

ISAKMP is the protocol that handles the negotiation of IPsec security associations, and its IKE exchanges run over UDP port 500 by default. This is the standard port administrators permit for IPsec VPN setup. In environments where devices are behind NAT, NAT Traversal uses UDP port 4500 to carry IPsec/NAT-T traffic, but the initial ISAKMP negotiations are still associated with port 500. The other ports relate to different VPN technologies (L2TP uses 1701, OpenVPN commonly uses 1194), while 4500 pertains to NAT traversal rather than the primary ISAKMP port.

ISAKMP is the protocol that handles the negotiation of IPsec security associations, and its IKE exchanges run over UDP port 500 by default. This is the standard port administrators permit for IPsec VPN setup. In environments where devices are behind NAT, NAT Traversal uses UDP port 4500 to carry IPsec/NAT-T traffic, but the initial ISAKMP negotiations are still associated with port 500. The other ports relate to different VPN technologies (L2TP uses 1701, OpenVPN commonly uses 1194), while 4500 pertains to NAT traversal rather than the primary ISAKMP port.