Lab Project 5 - Configure Inter-Vlan Routing

Credit: Chhai Lihov Inter-VLAN routing is configured in this topology because devices in different VLANs cannot communicate with each other by default. In your topology, you have: VLAN Network Example Gateway VLAN 10 172.16.10.0/24 172.16.10.1 VLAN 20 172.16.20.0/24 172.16.20.1 A Layer 2 switch (such as the Cisco 2960) separates VLANs into different broadcast domains. That means: • ✅ PC in VLAN 10 can communicate with another PC in VLAN 10. • ✅ PC in VLAN 20 can communicate with another PC in VLAN 20. • ❌ PC in VLAN 10 cannot communicate with a PC in VLAN 20 without a Layer 3 device. ________________________________________ Example Suppose: Laptop0 • IP: 172.16.10.10/24 • VLAN 10 • Gateway: 172.16.10.1 Laptop1 • IP: 172.16.20.10/24 • VLAN 20 • Gateway: 172.16.20.1 When Laptop0 tries to ping 172.16.20.10: 1. Laptop0 realizes the destination is in another subnet. 2. It sends the packet to its default gateway (172.16.10.1). 3. The router or Layer 3 switch routes the packet to VLAN 20. 4. The packet reaches Laptop1. 5. Laptop1 replies through its gateway (172.16.20.1). Without Inter-VLAN Routing, Step 3 never happens, so the ping fails. ________________________________________ Why each topology uses Inter-VLAN Routing 1. Legacy Inter-VLAN Routing Router G0/0 G0/1 | | VLAN10 VLAN20 \ / Layer2 Switch Purpose • The router has one physical interface for each VLAN. • Each interface acts as the default gateway for its VLAN. Advantages • Easy to understand. • Good for learning. Disadvantages • Requires one router interface per VLAN. • Not scalable. ________________________________________ 2. Router-on-a-Stick (ROAS) Router | Trunk Link | Layer2 Switch / \ VLAN10 VLAN20 Purpose • Uses one physical router interface. • Creates subinterfaces (e.g., G0/0.10 and G0/0.20). • A trunk carries traffic for multiple VLANs. Advantages • Saves router interfaces. • Supports many VLANs. Disadvantages • All VLAN traffic shares one physical link, which can become a bottleneck. ________________________________________ 3. Layer 3 Switch Inter-VLAN Routing Layer 3 Switch SVI VLAN10 SVI VLAN20 ip routing / \ Switch Switch Purpose • The Layer 3 switch performs routing itself using Switch Virtual Interfaces (SVIs). • No external router is needed. Advantages • Fastest routing (hardware-based). • Ideal for enterprise networks. • Supports many VLANs efficiently. Disadvantages • Requires a multilayer switch (e.g., Cisco Catalyst 3560). ________________________________________ Why learn all three methods? These three topologies demonstrate the evolution of Inter-VLAN routing: Method Routing Device Interfaces Needed Performance Typical Use Legacy Inter-VLAN Routing Router One interface per VLAN Low Learning and small legacy networks Router-on-a-Stick Router One trunk interface Medium Small to medium businesses Layer 3 Switch Multilayer Switch SVIs High Enterprise and campus networks ________________________________________ Learning Objective By configuring all three topologies, students will understand: • How VLANs isolate broadcast domains. • Why devices in different VLANs cannot communicate without Layer 3 routing. • The role of a default gateway. • How routers and Layer 3 switches route traffic between VLANs. • The differences between Legacy Inter-VLAN Routing, Router-on-a-Stick, and Layer 3 Switch Inter-VLAN Routing, including their advantages, limitations, and appropriate deployment scenarios.