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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?
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 CoPP policy is policing routing protocol traffic at 100 kbps, which may be insufficient during redistribution bursts. The exceeded drops indicate that some packets are being dropped, likely due to the burst size being too small. The fix is to increase the police rate or burst size to accommodate the redistribution traffic.
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
Redistribution generates many routing updates; the police rate is insufficient, leading to drops.
- ✗
The access-list is missing EIGRP protocol, causing EIGRP packets to be dropped.
Why it's wrong here
The ACL includes OSPF but not EIGRP; however, the drops are on matched traffic, not unmatched.
- ✗
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 one ACL is fine; it matches that ACL.
- ✗
The policy-map is applied to the input of the control-plane, but redistribution uses output.
Why it's wrong here
CoPP applies to incoming control-plane traffic, which includes routing updates.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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