Objectives
| # | Objective |
|---|
| 1 | Create VLANs 10 and 20 on the Layer 3 switch and assign access ports |
| 2 | Create SVI (Switched Virtual Interface) for VLAN 10 โ assign IP 192.168.10.1/24 |
| 3 | Create SVI for VLAN 20 โ assign IP 192.168.20.1/24 |
| 4 | Enable IP routing on the switch with the ip routing command |
| 5 | Configure PC IPs and gateways pointing to the SVI IPs, then test inter-VLAN ping |
| 6 | Open the L2 vs L3 Architecture Comparator โ understand how L3 switching differs from ROAS |
| 7 | Knowledge check โ SVIs, ip routing, SVI advantages and when to use each method |
Key Concepts
| Concept | What it means |
|---|
| Layer 3 Switch | A switch that performs Layer 2 forwarding and Layer 3 routing in hardware using ASICs. Routing is done internally at wire speed โ no external router needed. |
| SVI | Switched Virtual Interface โ a logical Layer 3 interface assigned to a VLAN. It has no physical port; instead it exists conceptually "inside" the switch fabric. The SVI IP becomes the default gateway for that VLAN. |
| ip routing | A single global command that enables L3 routing on the switch. Without it, the switch forwards at Layer 2 only โ SVIs exist but don't route between VLANs. |
| Hardware vs Software routing | ROAS routes in software on the router CPU. An L3 switch routes in hardware using dedicated CEF/TCAM tables. Wire-speed routing โ no bottleneck at the "stick". |
| Connected routes | When an SVI has an IP and is up, the switch automatically adds connected routes. No static routes or protocols needed for directly attached VLANs. |
Addressing Plan
| Device | Interface | IP Address | Role |
|---|
| PC1 | NIC | 192.168.10.10/24 | VLAN 10 โ gateway 192.168.10.1 |
| PC2 | NIC | 192.168.20.10/24 | VLAN 20 โ gateway 192.168.20.1 |
| SW1 | Vlan10 SVI | 192.168.10.1/24 | VLAN 10 gateway (SVI) |
| SW1 | Vlan20 SVI | 192.168.20.1/24 | VLAN 20 gateway (SVI) |
Key Commands โ SW1 (Layer 3 Switch)
| Command | Purpose |
|---|
| interface Vlan10 | Create / enter SVI for VLAN 10 |
| ip address 192.168.10.1 255.255.255.0 | Assign gateway IP to the SVI |
| no shutdown | Bring SVI up (SVIs are shutdown by default) |
| ip routing | Enable L3 routing on the switch โ critical command |
| show ip interface brief | Verify SVIs are up/up with correct IPs |
| show ip route | Confirm connected routes for VLAN 10 and VLAN 20 |
| show interfaces Vlan10 | Check SVI state in detail |
An SVI must have: (1) the VLAN created, (2) at least one access port in that VLAN that is up, (3) ip routing enabled, and (4) the SVI itself configured with no shutdown. All four are required for routing to work.
SVIs are shut down by default. You must explicitly run no shutdown on each SVI after assigning the IP. Without this, the SVI will be administratively down even if the VLAN exists and has active ports.