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300-410 Practice Question: Configures CoPP to protect the control plane, but…
A network engineer configures CoPP to protect the control plane, but after redistributing routes, some legitimate routing updates are dropped. Router R1 config: control-plane service-policy input COPP ! class-map match-all ROUTING match access-group name ROUTING ! policy-map COPP
class ROUTING
police 100000 15000 15000 conform-action transmit exceed-action drop !
access-list ROUTING permit tcp any any eq bgp access-list ROUTING permit udp any any eq 520 access-list ROUTING permit ospf any any R1# show policy-map control-plane input
Class-map: ROUTING (match-all) 100 packets, 10000 bytes 5 minute offered rate 0 bps drop rate 0 bps Match: access-group name ROUTING police: cir 100000 bps, bc 15000 bytes, be 15000 bytes conformed 90 packets, 9000 bytes; actions: transmit exceeded 10 packets, 1000 bytes; actions: drop
What is the root cause?
⚠ Common exam trap
The trap is assuming that the access-list is incomplete or that the class-map configuration is wrong, when the statistics clearly show drops due to the policer; candidates might overlook the low CIR value and focus on other details.
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 CoPP police rate is too low for the volume of routing updates during redistribution, causing drops.
The output shows that 10 packets were exceeded and dropped by the policer. The CoPP policy is configured with a committed information rate (CIR) of 100000 bps (100 kbps), which is relatively low for routing updates during redistribution. When routes are redistributed, there can be a burst of routing protocol packets (BGP, OSPF, etc.) that exceeds this rate, causing the policer to drop legitimate updates. The root cause is that the police rate is too low for the volume of routing updates.
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 CoPP police rate is too low for the volume of routing updates during redistribution, causing drops.
Why this is correct
The police counters show 10 packets exceeded the configured rate and were dropped, while offered rate sits at 0 bps. The 100000 bps CIR is insufficient for the burst of routing updates triggered by redistribution, so legitimate BGP, OSPF or RIP traffic is discarded.
- ✗
The access-list is missing EIGRP protocol, causing EIGRP packets to be dropped.
Why it's wrong here
EIGRP is not redistributed here, and the ACL already permits OSPF and BGP; the counters show drops from the policer's exceed-action, not a missing match. EIGRP would need adding only if EIGRP adjacencies were being policed, which the redistribution scenario does not indicate.
- ✗
The class-map is match-all, which requires all conditions to match, but only one ACL is present.
Why it's wrong here
match-all with a single match statement behaves identically to match-any, since one condition is trivially satisfied; the ACL matches and packets are counted. match-all would matter only with multiple match statements requiring simultaneous satisfaction, which this class-map does not have.
- ✗
The policy-map is applied to the input of the control-plane, but redistribution uses output.
Why it's wrong here
CoPP inherently polices traffic destined to the control plane, so input is the correct direction; redistribution-generated updates arrive inbound and are matched. Output policing applies to locally originated traffic leaving the router, which is not where CoPP protects the RP.
Visual reference
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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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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