A classful routing topology is useful for understanding the history of IPv4 addressing, but modern networks use classless addressing and CIDR. This lab lets you compare the two approaches.
Historical Address Classes
- Class A used a default /8 mask.
- Class B used a default /16 mask.
- Class C used a default /24 mask.
These defaults are historical. Current routing decisions use an explicitly configured prefix length.
Build the Lab
- Create three routers connected in a line.
- Attach a LAN to each edge router.
- Assign unique subnets and document every prefix.
- Configure interfaces and verify they are up.
- Add static routes or a suitable dynamic routing protocol.
- Test forward and return connectivity.
Classful Protocol Comparison
Older classful routing protocols did not include subnet-mask information in updates and could not properly support discontiguous networks or variable-length subnet masks. RIPv1 is a common historical example.
Modern Classless Design
Modern networks use CIDR and protocols that carry prefix-length information. This supports variable-length subnetting, summarization, more efficient address use, and clearer routing decisions.
Verification Commands
show ip interface briefshow ip routeshow ip protocolspingtraceroute
Troubleshooting Exercise
Introduce an incorrect mask, missing return route, or disabled interface. Record the symptom, identify the failed layer, correct one issue at a time, and verify the complete path.
Continue Your CCNA Preparation
Use our CCNA routing topology labs. For structured practice, see the CCNA 200-301 Premium PDF with the latest available questions and answers.
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