CND Practice Question: Network Security Controls Protocols And Devices

An organization is configuring an IPsec VPN tunnel between two branch offices using Cisco IOS routers. The engineering team requires the use of a secure key exchange method that provides perfect forward secrecy (PFS) during the Phase 1 Internet Key Exchange (IKEv1) negotiation. Which Phase 1 mode must be selected?

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Main Mode

Main Mode in IKEv1 protects the identity of the peers and uses Diffie-Hellman exchanges to derive keying material, which ensures Perfect Forward Secrecy (PFS) for the phase 2 keys derived from it. Aggressive Mode does not protect peer identities.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Transport Mode
Why it's wrong here
Transport mode is an IPsec security protocol mode (used in both AH and ESP), not an IKEv1 Phase 1 negotiation mode.
✗
Aggressive Mode
Why it's wrong here
Aggressive Mode compresses the exchange into fewer packets for speed but compromises identity protection and does not provide robust PFS for the initial exchange.
✓
Main Mode
Why this is correct
Main Mode uses a six-message exchange that protects identity and incorporates a Diffie-Hellman exchange, ensuring PFS for the IPsec security associations.
✗
Quick Mode
Why it's wrong here
Quick Mode is used for IKEv1 Phase 2 negotiations to establish the actual data-transfer security associations, not Phase 1.

Quick reference

VPN Protocol Comparison

Protocol	Port	Encryption	Authentication	Use Case
IKEv2 / IPsec	UDP 500 / 4500	AES-256	Certificates / PSK	Site-to-site & remote access
SSL / TLS VPN	TCP 443	TLS 1.3	Certificates / MFA	Clientless remote access
L2TP / IPsec	UDP 1701	AES (IPsec)	PSK / Certificates	Legacy remote access
WireGuard	UDP 51820	ChaCha20	Public keys	Modern high-performance VPN
PPTP	TCP 1723	MPPE (weak)	MS-CHAPv2	Legacy — avoid in production

PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.

About these practice questions

Courseiva writes every CND question from scratch — 323 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →

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Written and reviewed by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

Last reviewed August 2026 · checked against the official EC-Council exam blueprint

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