Which protocol and port number are used by default for IKE Phase 1 negotiations in an IPSec VPN?

The correct answer is D. UDP 500. IKE (Internet Key Exchange) Phase 1 uses UDP port 500 by default to establish the secure channel and negotiate encryption parameters between VPN peers. UDP is used because IKE is a lightweight negotiation protocol that does not require TCP's connection overhead. When NAT is…

VPN Configuration

Question

Options

ATCP 22
BTCP 443
CUDP 4500
DUDP 500

How the community answered

(34 responses)

A
3% (1)
B
6% (2)
D
91% (31)

Explanation

IKE (Internet Key Exchange) Phase 1 uses UDP port 500 by default to establish the secure channel and negotiate encryption parameters between VPN peers. UDP is used because IKE is a lightweight negotiation protocol that does not require TCP's connection overhead. When NAT is detected between the two VPN peers (NAT-Traversal / NAT-T), IKE switches to UDP port 4500 to encapsulate ESP packets and avoid NAT compatibility issues. TCP 22 is SSH, TCP 443 is HTTPS, and UDP 4500 is specifically the NAT-T fallback port, not the default.

Topics

#IPSec VPN#IKE Phase 1#UDP 500#Network Protocols

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