NSE7 Advanced VPN and Zero Trust Practice Question
An administrator is troubleshooting an OSPF over IPsec VPN overlay. The OSPF neighbor state is stuck in EXSTART. The VPN tunnel is up. Which TWO issues could cause this?
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
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IP fragmentation issue due to GRE/IPsec overhead
A stuck EXSTART state often indicates issues with the maximum transmission unit (MTU) or fragmentation, preventing OSPF packets from being exchanged properly. MTU mismatch or fragmentation due to encapsulation overhead can cause this.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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