How to configure a Layer 3 Switch for inter-VLAN routing

Layer 3 Switch: A multilayer switch can perform both switching and routing functions. It is ‘Layer 3 aware’, meaning it can operate at the network layer of the OSI model. You can assign IP addresses to its interfaces, similar to how you would with a router. Virtual interfaces can be created for each VLAN, and each can be assigned an IP address. You can also configure routes on a multilayer switch, just like a router. These switches are commonly used for inter-VLAN routing, allowing communication between different VLANs without requiring an external router.   SVIs (Switch Virtual Interfaces) are virtual interfaces on a multilayer switch to which you can assign IP addresses. Each PC should be configured to use the SVI (not the router) as its gateway address. To send traffic between different subnets/VLANs, PCs send their traffic to the switch, and the switch routes the traffic between VLANs. To enable an SVI (Switch Virtual Interface) on a switch, the following conditions must be met: 1.       The VLAN must exist on the switch. 2.       The switch must have at least one access port in the VLAN in an up/up state, and/or one trunk port that allows the VLAN that is in an up/up state. 3.       The VLAN must not be shutdown (the shutdown command can disable a VLAN). 4.       The SVI must not be shutdown (SVIs are disabled by default). Syntax: Interface vlan <Vlan ID> Ip address <IP Address> <subnet mask> IP routing This command enables the layer 3 functions in the L3 switch Int gi0/0 No switchport This configures the interface as a ‘routed port’, which means it's a Layer 3 port and not a Layer 2 switchport.   #Ntworking #switch #Coreswitch #Tagging #Vlan

💡 OSI 7 Layers Model ✅ Physical Layer (Layer 1) Deals with hardware transmission of raw data bits over physical media (cables, fiber, radio waves). Defines connectors, voltage levels, frequencies, and data rates. 🔵Examples: Ethernet cables, Fiber optics, Hubs. ✅Data Link Layer (Layer 2) Provides error detection and framing for reliable node-to-node data transfer. Uses MAC addresses for device identification in the same network. 🔵Examples: Switches, Ethernet, Wi-Fi (802.11). ✅Network Layer (Layer 3) Responsible for logical addressing, routing, and forwarding of data packets across networks. Uses IP addresses. 🔵Examples: Routers, IP (IPv4/IPv6), ICMP. ✅Transport Layer (Layer 4) Ensures end-to-end communication, error recovery, and data segmentation. Uses ports to identify applications. 🔵Examples: TCP (reliable, connection-oriented), UDP (fast, connectionless). ✅Session Layer (Layer 5) Manages sessions (connections) between applications. Handles authentication, authorization, and session recovery. 🔵Example: NetBIOS, Remote Procedure Call (RPC). ✅Presentation Layer (Layer 6) Translates, encrypts, and compresses data for the application layer. Ensures compatibility between different systems. 🔵Examples: SSL/TLS (encryption), JPEG, GIF, MPEG. ✅Application Layer (Layer 7) Closest to the end user. Provides services and interfaces for applications to communicate over a network. 🔵Examples: HTTP/HTTPS (web), FTP, SMTP (email), DNS. ✅ In short: Layer 1–2: Data delivery in the same network (hardware & LAN). Layer 3–4: Data delivery between networks (IP & ports). Layer 5–7: User interaction, data representation, and application communication.

Static routing is a network configuration method in which routes are manually set up by the network administrator. Unlike dynamic routing protocols, static routes do not change automatically; they remain fixed until manually modified. When configuring IP static routing, an administrator manually defines the path (next-hop IP address or exit interface) that packets should take to reach a specific destination network. Key Points of Static Routing: Manual Configuration: Routes are entered manually by the administrator. Next-Hop & Interface: Specifies the next-hop router’s IP address or the outgoing interface. Simplicity: Easy to configure on small networks. Control: Provides complete control over routing paths. Low Resource Usage: Does not consume CPU or bandwidth for routing updates like dynamic protocols. Limitation: Not scalable for large or frequently changing networks.

The OSI (Open Systems Interconnection) model is a framework used to understand how data moves across a network. It divides network communication into 7 layers, each with a specific function. The 7 Layers of OSI Model (Bottom to Top) Layer 1 – Physical Layer Deals with actual hardware and transmission of raw bits (0s and 1s). Cables, switches, hubs Defines how devices are physically connected and how bits are transmitted. Layer 2 – Data Link Layer Responsible for node-to-node communication and error detection. Uses MAC addresses to identify devices on the same network. Switches, bridges. Ethernet, PPP, VLAN. Layer 3 – Network Layer Handles routing and logical addressing (IP addresses). Determines the best path for data between devices across networks. Routers. IP, ICMP, OSPF, BGP. Layer 4 – Transport Layer Ensures reliable data delivery and error recovery. Uses ports to direct data to the correct application. TCP (reliable), UDP (fast, unreliable). Segmentation, flow control, error checking. Layer 5 – Session Layer Manages sessions or connections between devices. Handles starting, maintaining, and ending communication sessions. NFS, SQL, RPC. Layer 6 – Presentation Layer Translates data into a format that the application can understand. Handles encryption, decryption, compression. SSL/TLS, JPEG, MPEG, ASCII. Layer 7 – Application Layer Closest to the end-user; provides network services to applications. HTTP, HTTPS, FTP, SMTP, DNS. Allows users and software to interact with the network.

I have implemented a VLAN segmentation and inter-VLAN routing setup using one Layer 3 switch and two Layer 2 access switches. VLAN Creation: VLAN 10 and VLAN 20 were created to logically segment the network. Devices in VLAN 10 and VLAN 20 were assigned to different ports on the Layer 2 switches. Trunk Configuration: The uplink ports between the Layer 2 switches and the Layer 3 switch were configured as 802.1Q trunk links, carrying traffic for both VLANs. Inter-VLAN Routing: On the Layer 3 switch, SVIs (Switch Virtual Interfaces) were created for VLAN 10 and VLAN 20, each assigned an IP address to serve as the default gateway for devices in the respective VLANs. IP routing was enabled on the Layer 3 switch, allowing devices in VLAN 10 and VLAN 20 to communicate with each other through Layer 3 switching. Result: Devices connected to VLAN 10 and VLAN 20, even though separated by different Layer 2 switches, can now communicate successfully via the Layer 3 switch. This design improves network segmentation, scalability, and security while still allowing controlled communication between VLANs

❇️Inter-VLAN Routing❇️ ✅It is a method to enable communication between two different VLANs connected in a network device like network switch or a router. ✅A Router, Layer 3 switch or any other layer 3 device is needed to enable it. ✅The VLANs must be in different network. ✅ Between the layer 2 and layer 3 device the link should be in trunking state. ❇️Router-Switch❇️ ✅The router is connected to the switch using a single interface. ✅The switchport connecting to the router is configured as a trunk link. ✅The single interface on the router is then configured with multiple IP addresses that correspond to the VLANs on the switch. ✅This interface accepts traffic from all the VLANs and determines the destination network based on the source and destination IP in the packets. It then forwards the data to the switch with the correct VLAN information. ✅In this type of inter-VLAN routing, the interface connecting the router to the switch is usually a trunk link. ✅The router accepts traffic that is tagged from the VLANs on the switch through the trunk link. ✅On the router, the physical interface is divided into smaller interfaces called subinterfaces. ✅When the router receives the tagged traffic, it forwards the traffic out to the subinterface that has the destination IP address. ✅Sub interfaces aren’t real interfaces but they use the LAN physical interfaces on the router to forward data to various VLANs. ✅Each sub interface is configured with an IP address and assigned a VLAN based on the design.

🚀✅Understanding the OSI Model in Networking The OSI (Open Systems Interconnection) model is a crucial framework for understanding and troubleshooting network systems. It breaks down the complex process of data transmission into 7 distinct layers, from physical transmission all the way to the application layer. 🌐 Here’s a breakdown of the OSI layers: 1️⃣ Physical - Media, signal, and binary transmission (Ethernet, RS-232, DSL, etc.) 2️⃣ Data Link - Addressing, error detection, and flow control (Ethernet, MAC addresses) 3️⃣ Network - Logical addressing, routing, and path determination (IP, ARP, OSPF) 4️⃣ Transport - End-to-end connection reliability and flow control (TCP, UDP, SSL/TLS) 5️⃣ Session - Session management and communication (TCP, SIP, RPC) 6️⃣ Presentation - Data representation and encryption (HTML, JPEG, MP3) 7️⃣ Application - Network services like email, web browsing, and file transfer (HTTP, FTP, SMTP) This model helps IT professionals manage network communications effectively and ensure smooth data flow across systems. 🛠️📊.

Static Routing 📡 Static Routing is a routing method where the network administrator 🧑💻 manually enters routes into the router instead of using automatic updates. It is simple, predictable, and requires less CPU power ⚡, which makes it useful in small networks, labs 🏫, or troubleshooting 🛠. In static routing, the admin specifies which network 🌐 can be reached through which next-hop router ➡️. For example, if Router 1 needs to reach a network connected to Router 3, the administrator adds a route via Router 2 as the next hop. This ensures proper communication 🔗 between all devices. However, static routing also has limitations 🚫. It is not scalable for large networks because every route must be added and updated manually. It also lacks flexibility, meaning if one path goes down ❌, the router will not automatically find another route. 👉 In short, static routing is best for small or simple networks 🏠, but for large and complex environments 🌍, dynamic routing protocols like RIP, OSPF, or BGP 🔀 are preferred.

✍️1. Bus Topology All devices share a single backbone cable. Simple and cost-effective, but failure of backbone stops the whole network. ✍️2. Star Topology All devices connect to a central hub or switch. Easy to manage and troubleshoot. If the central device fails, the network goes down. ✍️3. Ring Topology Devices are connected in a closed loop (ring). Data travels in one direction around the ring. Failure of one device can disrupt the whole network. ✍️4. Mesh Topology Every device connects directly to every other device. High reliability, no single point of failure. Requires many cables, very expensive. ✍️5. Tree Topology Combination of Star and Bus topologies, in a hierarchical structure. Suitable for large organizations. Scalable, but backbone failure affects the entire network. ✍️6. Hybrid Topology Combination of two or more topologies (e.g., Star + Ring). Flexible and reliable. Complex to design and implement

What is the OSI Model? The OSI (Open Systems Interconnection) model is a framework that explains how data moves from one device to another across a network. It’s divided into 7 layers, each with its own role: 1) Physical → cables and signals 2) Data Link → switching, MAC addressing, error detection 3) Network → IP addressing and routing 4) Transport → ensures data arrives correctly (TCP/UDP) 5) Session → manages connections between apps 6) Presentation → data formatting, compression, encryption 7) Application → where users interact (email, web, apps) Why is it important? Because it gives us a common language to describe how networks work. Whether you’re troubleshooting WiFi or designing global infrastructure — the OSI model is the map that keeps us aligned. In short: The OSI model = the foundation of networking.