hardMultiple ChoiceObjective-mapped
300-410 Practice Question: A router has CoPP configured with a class-map…
A router has CoPP configured with a class-map that matches all traffic and polices it to 10000 pps. The router also has IPsec configured for a site-to-site VPN. After applying CoPP, the IPsec tunnel goes up, but traffic through the tunnel is intermittently dropped. Which is the most likely explanation?
⚠ Common exam trap
Cisco often tests the distinction between control plane and data plane traffic, and the trap here is that candidates mistakenly think CoPP affects all traffic (including ESP data plane) rather than only control plane traffic like IKE.
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
✓
CoPP drops IKE packets during rekey, causing the IPsec tunnel to fail temporarily.
CoPP polices control plane traffic, and IKE (UDP 500/4500) is control plane traffic. During IPsec rekey, IKE packets are sent to the router's control plane for processing. If CoPP drops these IKE packets due to the 10000 pps policer, the rekey fails, causing the IPsec tunnel to temporarily go down until the next rekey attempt. The tunnel itself stays up initially, but traffic is intermittently dropped because the tunnel fails during rekey events.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
CoPP drops ESP packets, which are data plane traffic.
Why it's wrong here
ESP packets are data plane and should not hit the control plane unless they are destined to the router.
- ✓
CoPP drops IKE packets during rekey, causing the IPsec tunnel to fail temporarily.
Why this is correct
IKE packets are control plane; if dropped, the tunnel may not rekey properly, causing traffic loss.
- ✗
IPsec uses TCP, and CoPP only polices UDP.
Why it's wrong here
IKE uses UDP, and ESP is IP protocol 50.
- ✗
The CoPP policy is applied to the tunnel interface, not the control plane.
Why it's wrong here
CoPP is applied to the control plane.
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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