300-410 Infrastructure Security Practice Question
A network engineer is configuring IPsec VPN on a Cisco IOS router. The engineer wants to ensure that only traffic from the 10.1.1.0/24 subnet to the 10.2.2.0/24 subnet is encrypted, while all other traffic is sent unencrypted. The engineer also wants to use a pre-shared key for authentication. Which configuration element is required to define the interesting traffic?
⚠ Common exam trap
Many exam-takers confuse the crypto map's 'match address' command with the ACL itself; the ACL is the actual definition of interesting traffic.
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
✓
access-list 101 permit ip 10.1.1.0 0.0.0.255 10.2.2.0 0.0.0.255
The interesting traffic is defined by an extended ACL that matches the source and destination subnets. This ACL is then referenced in the crypto map using the 'match address' command. The ACL specifies which packets are encrypted and sent through the VPN tunnel, while all other traffic is sent unencrypted. The other options are part of the IPsec configuration but do not define the traffic to be encrypted.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
access-list 101 permit ip 10.1.1.0 0.0.0.255 10.2.2.0 0.0.0.255
Why this is correct
The extended ACL defines the interesting traffic that should be encrypted by the IPsec VPN. In this case, it permits IP traffic from 10.1.1.0/24 to 10.2.2.0/24. This ACL is then referenced in the crypto map with 'match address 101'. Without this ACL, the router would not know which traffic to encrypt, making it the essential element for defining interesting traffic.
- ✗
crypto isakmp policy 10 authentication pre-share
Why it's wrong here
The 'crypto isakmp policy' command defines the ISAKMP (IKE) policy parameters, including authentication method, encryption, hash, and Diffie-Hellman group. While it sets pre-shared key authentication, it does not define which traffic is interesting for encryption. That is the role of the crypto ACL. Therefore, this configuration element alone does not specify the traffic to be encrypted.
- ✗
crypto map MYMAP 10 ipsec-isakmp set peer 203.0.113.2 set transform-set MYSET match address 101
Why it's wrong here
The crypto map defines the policy for IPsec, including the peer, transform set, and the ACL that matches interesting traffic via 'match address 101'. However, the question asks for the configuration element that defines the interesting traffic itself, which is the ACL referenced by the crypto map. The crypto map is the mechanism that ties the ACL to the IPsec policy, but the ACL is what actually specifies the traffic.
- ✗
crypto ipsec transform-set MYSET esp-aes esp-sha-hmac
Why it's wrong here
The transform set defines the encryption and integrity algorithms for the IPsec tunnel, such as ESP with AES and SHA-HMAC. It does not determine which traffic is encrypted. The transform set is applied within the crypto map, but it only specifies how to protect the traffic, not what traffic to protect. Thus, it is not the configuration element that defines interesting traffic.
Visual reference
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.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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