Layer 3 switch

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

A multilayer switch is a network switch that performs forwarding at multiple protocol layers, including the data link and network layers.

A Layer 3 switch, also called a multilayer switch, combines switching with packet routing. It commonly performs inter-VLAN routing without requiring an external router. section 12.4.2 section 12.5

Understand its main operating pieces:

• Uses switch virtual interfaces (SVIs), such as interface vlan 10, as Layer 3 gateways for VLAN hosts. section 12.4.2
• Requires ip routing before it can forward packets between VLANs or subnets. section 12.4.2
• Can convert a physical switch port into a routed port with no switchport, then assign it an IP address. section 12.4.2
• Removes the need for an external router when SVIs provide all required inter-VLAN routing. section 12.4.2

Configure SVIs for inter-VLAN routing

SW1(config)# ip routing SW1(config)# interface vlan 10 SW1(config-if)# ip address 172.16.1.1 255.255.255.192 SW1(config)# interface vlan 20 SW1(config-if)# ip address 172.16.1.65 255.255.255.192 These commands enable routing and assign gateway addresses to VLAN 10 and VLAN 20. Verify the result with show ip interface brief and show ip route; the SVIs should appear up/up with connected routes. section 12.4.2

Figure 12.11 SW1, a multilayer switch, routes a packet from PC1 to PC5. SW1 has three SVIs: VLAN 10 (172.16.1.1), VLAN 20 (172.16.1.65), and VLAN 30 (172.16.1.129), allowing SW1 to route packets internally, without relying on an external router.

Trace a packet moving from PC1 in VLAN 10 to PC5 in VLAN 30. The switch receives the frame at the VLAN 10 SVI, routes internally, and forwards a new VLAN 30 frame toward PC5. section 12.4.2

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes

Explains SVI routing, required commands, verification output, and routed ports, while stopping short of detailed routing protocol behavior.

Examples

Uses VLAN 10, VLAN 20, and VLAN 30 SVIs, packet forwarding diagrams, Cisco IOS configuration, and routing-table verification.

What it assumes

Assumes VLAN and subnet concepts while establishing how Layer 2 segmentation connects to Layer 3 routing.

What you can do after

Operate/configure Cisco IOS inter-VLAN routing with ip routing, SVI addresses, routed ports, and verification commands.

How it connects

Connects VLANs, subnets, inter-VLAN routing, SVIs, trunks, default gateways, external routers, and router-on-a-stick.

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Related concepts

• network switchkind of · A network switch is a device that connects devices within a local network and selectively forwards data-link-layer frames to their intended destinations.
• switch virtual interfaceuses · A switch virtual interface is a virtual Layer 3 interface on a switch that provides an IP interface for a VLAN, management, or routing.
• inter-vlan routingimplements · Inter-VLAN routing is the forwarding of traffic between subnets associated with different VLANs in a segmented local network.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.