Network Fundamentals

Course at a glance

• 164 lessons in 20 units.
• Format: self-paced lessons with Cisco IOS configurations, packet captures, and video.
• Last updated: October 2026.

What is networking?

Networking means connecting computers and other devices so they can communicate and share information, files, printers, and applications. A network can be as small as two directly connected computers or as large as the Internet. We build networks with devices like switches, routers, and firewalls, and all of them use standard protocols like Ethernet and IP to exchange data.

To make devices from different vendors work together, networking is built in layers, described by the OSI model. Each layer has its own job. Switches forward Ethernet frames within a local network based on MAC addresses. Routers forward IP packets between networks based on IP addresses. TCP and UDP deliver data to the right application, and services like DHCP, DNS, and NAT make it all work for users. Once you understand these layers, you can figure out how any network protocol works and where to look when something breaks.

Who needs network fundamentals? Anyone who wants to become a network engineer, and anyone who works with servers, cloud, security, or automation, since all of it runs on the network. These fundamentals are also the foundation of every advanced topic, from OSPF and BGP to VXLAN and SD-WAN.

Network Fundamentals Learning Roadmap

This roadmap follows the course units. Each topic has a short explanation and links to the lessons where we cover it in detail.

Networking Basics and the OSI Model

We start with what a network is, the devices we use, and the different network topologies. The OSI model splits networking into seven layers, and the TCP/IP model combines some of them into four. You’ll learn how Ethernet works on the LAN, and what collision domains and broadcast domains are. At the transport layer, TCP and UDP take different approaches: TCP offers reliable delivery, while UDP is best effort. ICMP is used by tools like ping and traceroute.

IPv4 and IPv6 Addressing

Every device on a network needs an IP address. An IPv4 address is 32 bits, and the subnet mask tells you which part is the network and which part is the host. You’ll learn how to subnet in binary and decimal, and how ARP finds the MAC address that belongs to an IP address. IPv6 uses 128-bit addresses written in hexadecimal, and hosts can configure an address themselves with stateless autoconfiguration.

Switching, VLANs and Spanning Tree

A switch learns which MAC addresses live behind which interface and forwards frames only where they need to go. VLANs split a switch into multiple broadcast domains, trunks carry multiple VLANs between switches with 802.1Q tags, and InterVLAN routing lets the VLANs talk to each other. Redundant links between switches cause loops, so spanning tree blocks some of them; RSTP converges much faster than classic STP. EtherChannel bundles multiple physical links into one logical link, so spanning tree doesn’t block them.

Routing Fundamentals and WANs

Routers forward IP packets between networks based on their routing table. You’ll configure static routes, and learn how a router chooses between routes with administrative distance and longest prefix match. To connect sites over large distances, we use WANs, with protocols like HDLC and PPP on serial links. A GRE tunnel creates a virtual point-to-point link between two routers, for example over the Internet.

OSPF, EIGRP and Gateway Redundancy

Dynamic routing protocols learn routes from neighbors and find a new path when a link fails. OSPF is a link-state protocol: every router builds a map of its area and calculates the lowest cost path. EIGRP, created by Cisco, is an advanced distance vector protocol. Hosts only have a single default gateway, so first hop redundancy protocols like HSRP, VRRP, and GLBP create a virtual gateway that keeps working when a router fails.

NAT, Access-Lists, DHCP and DNS

NAT translates private IP addresses to public ones, and PAT lets many hosts share a single public IP address by using port numbers. Access-lists filter or classify traffic: standard access-lists only match the source address, extended access-lists also match the destination, protocol, and ports. DHCP hands out IP addresses automatically, and DNS translates hostnames into IP addresses.

Network Management and QoS

To manage a network, you need to know what is connected where, what time it is, and what is happening. CDP and LLDP discover neighbor devices, NTP synchronizes clocks so log timestamps are accurate, SNMP lets a management system monitor your devices, and syslog messages have eight severity levels. QoS gives important traffic like voice priority over other traffic, starting with classification and marking with IP precedence and DSCP values.

Cloud, Automation and Network Design

Networks are no longer only boxes you configure one by one. You’ll learn the cloud service models (IaaS, PaaS, and SaaS) and deployment models, what SDN is, and how to get started with Python, Ansible, and Terraform. We also look at AI and machine learning in networking. Finally, we cover network design: the access, distribution, and core layers of a campus network, the spine and leaf architecture of the data center, and overlay networks.

Ready for the next step?

Network Fundamentals is free. When you are ready to go further, sign up to get access to every other course on NetworkLessons.com, from OSPF and BGP to MPLS and SD-WAN.

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