hardMultiple Choice
300-410 Practice Question: An engineer configures CoPP on a router running…
An engineer configures CoPP on a router running EIGRP. The policy includes a class-map matching EIGRP traffic with a police rate of 1000 pps. After applying the policy, EIGRP neighbors form but occasionally go active and become stuck-in-active (SIA). Which is the most likely explanation?
⚠ Common exam trap
It's easy for candidates to assume CoPP only affects incoming traffic or that EIGRP uses TCP, but the key is understanding that EIGRP's reliable packets (queries/replies) are sensitive to drops, and a low pps police rate can cause SIA.
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 police rate in pps is too low, causing EIGRP reliable packets (queries/replies) to be dropped, leading to SIA.
EIGRP uses RTP (Reliable Transport Protocol) for certain packets like queries and replies. These reliable packets require acknowledgment; if the CoPP police rate of 1000 pps is too low, EIGRP queries or replies may be dropped. Missing acknowledgments cause the neighbor to be declared active, and if the query process is not completed within the active timer, the route becomes stuck-in-active (SIA).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
EIGRP uses multicast, and CoPP cannot police multicast traffic.
Why it's wrong here
CoPP class-maps can match multicast destination addresses, and EIGRP multicast hellos are policed like any other control-plane traffic. The claim is tempting because multicast handling differs elsewhere, but policing rate, not multicast itself, causes the SIA.
- ✓
The police rate in pps is too low, causing EIGRP reliable packets (queries/replies) to be dropped, leading to SIA.
Why this is correct
CoPP polices matched traffic in packets per second. EIGRP relies on reliable transport for queries and replies, so a 1000 pps limit drops those retransmissions under load, preventing acknowledgement and leaving neighbours stuck-in-active. Raising the rate restores reliable delivery.
- ✗
CoPP only affects incoming traffic, but EIGRP SIA is caused by outgoing packet drops.
Why it's wrong here
CoPP polices ingress traffic on the control plane interface, and EIGRP SIA arises from dropped inbound hello or update packets, not outbound ones. This option is tempting because SIA involves retransmissions, but those are triggered by missing inbound acknowledgements.
- ✗
EIGRP uses TCP, and CoPP only polices UDP.
Why it's wrong here
EIGRP is a protocol that runs directly over IP using protocol number 88, so it is neither TCP nor UDP; CoPP class-maps match it via IP protocol, not transport ports. The option is tempting because CoPP commonly polices TCP and UDP management traffic, but EIGRP's transport differs entirely.
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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