hardMultiple Choice
300-410 Practice Question: In Cisco IOS, what is the default encryption…
In Cisco IOS, what is the default encryption algorithm for IKEv1 phase 1 if not specified in the ISAKMP policy?
⚠ Common exam trap
Cisco often tests the default encryption algorithm for IKEv1 phase 1, and the trap here is that candidates assume a stronger algorithm like AES or 3DES is the default, but Cisco IOS defaults to the weaker DES for backward compatibility.
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
✓
DES
In Cisco IOS, when an IKEv1 ISAKMP policy is configured without specifying an encryption algorithm, the default encryption algorithm is DES (Data Encryption Standard). This is because Cisco IOS defaults to DES for IKEv1 phase 1 if no encryption is explicitly defined in the ISAKMP policy, as per the default policy parameters. DES uses a 56-bit key and is considered weak by modern standards, but it remains the default for backward compatibility.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AES 256
Why it's wrong here
Cisco IOS defaults to DES for IKEv1 phase 1 when no encryption is stated in the ISAKMP policy; AES 256 must be configured explicitly. It is tempting because AES is the modern standard, so engineers assume it is the implicit default.
- ✗
3DES
Why it's wrong here
Cisco IOS defaults IKEv1 phase 1 encryption to DES, not 3DES; 3DES must be configured explicitly with the encryption 3des command. It is tempting because 3DES is a widely deployed legacy cipher and appears in many sample ISAKMP policies, making it the correct choice only where the policy explicitly specifies it.
- ✓
DES
Why this is correct
Cisco IOS applies DES as the default IKEv1 phase 1 encryption when no encryption keyword is configured in the ISAKMP policy. DES provides only 56-bit symmetric encryption, so explicit configuration of AES is required for stronger phase 1 protection.
- ✗
AES 128
Why it's wrong here
AES 128 is never the IOS default for IKEv1 phase 1; the default is DES, and AES requires explicit configuration via the encryption aes command. It tempts because AES 128 is the modern recommended cipher, so it would be correct where the policy explicitly selects AES rather than relying on defaults.
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.
Go deeper
Related to this question
About these practice questions
One of 1,401 original 300-410 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.