mediumMultiple Choice
300-410 Practice Question: Given the partial configuration: crypto isakmp…
Given the partial configuration:
crypto isakmp policy 10
encryption aes 256 authentication pre-share group 14 !
crypto isakmp key cisco123 address 0.0.0.0 0.0.0.0
!
crypto ipsec transform-set TSET esp-aes 256 esp-sha-hmac
mode tunnel !
crypto map CMAP 10 ipsec-isakmp
set peer 192.168.1.2 set transform-set TSET match address 101 !
interface GigabitEthernet0/1 ip address 192.168.1.1 255.255.255.0 crypto map CMAP
!
access-list 101 permit ip 10.1.1.0 0.0.0.255 10.2.2.0 0.0.0.255
What is the effect of the 'crypto isakmp key' command with address 0.0.0.0 0.0.0.0?
⚠ Common exam trap
Cisco often tests the misconception that the crypto map's `set peer` command restricts which peers can authenticate with the pre-shared key, but in reality, the ISAKMP key wildcard overrides that restriction at the IKE layer.
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
✓
The key will be accepted from any peer, creating a security vulnerability.
The `crypto isakmp key` command with address `0.0.0.0 0.0.0.0` acts as a wildcard, meaning the pre-shared key will be accepted from any peer IP address during IKE Phase 1 authentication. This effectively disables peer-specific validation, allowing any device that knows the key to establish an ISAKMP SA, which is a significant security vulnerability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The key will be used only for peer 192.168.1.2 because the crypto map specifies that peer.
Why it's wrong here
The wildcard 0.0.0.0 0.0.0.0 matches any peer, so the key applies to all ISAKMP peers, not solely the crypto map peer. A specific address mask would restrict the key to one peer; the wildcard is used when many peers share one pre-shared key.
- ✓
The key will be accepted from any peer, creating a security vulnerability.
Why this is correct
The wildcard address 0.0.0.0 0.0.0.0 matches every peer, so the preshared key is offered to any device initiating IKE. This removes peer authentication by address, allowing an unauthorised host to complete phase 1 and establishing a genuine security weakness.
- ✗
The configuration will fail because the key must specify a specific peer address.
Why it's wrong here
Cisco IOS accepts the wildcard 0.0.0.0 0.0.0.0 mask, which defines a key valid for any peer address. A specific peer address is only required when the administrator wants to scope the key to a single remote gateway.
- ✗
The key will be ignored because there is no ISAKMP policy with a lifetime.
Why it's wrong here
ISAKMP policy lifetime defaults to 86400 seconds and need not be configured for the key to apply. The wildcard key is matched during aggressive or main mode against any peer, so it is used, not ignored.
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
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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.