Modern networks are no longer built entirely from physical servers, physical switches and one device per function. In this lesson you'll learn the basics of virtual machines, hypervisors, virtual switching, containers, cloud networking and common architectural ideas used in today's networks.
Traditionally, a server workload might have required its own physical machine. Virtualisation allows several independent systems to share the CPU, memory, storage and network interfaces of one physical host.
CPU, RAM, storage and NICs
Provides virtual hardware
Independent guest systems
Runs directly on the physical hardware and hosts virtual machines. This model is common in data centres and enterprise virtualisation.
Runs as an application on top of a conventional host operating system and is common in desktop or lab environments.
A virtual switch performs Layer 2 forwarding for virtual network interfaces. It provides connectivity between virtual machines and can connect them to physical network interfaces on the host.
Virtual NIC
Software Layer 2 forwarding
Connection to physical LAN
Containers isolate applications while sharing the host operating system kernel. They normally require fewer resources than running a complete guest operating system for every workload.
Includes a complete guest operating system running on virtualised hardware.
Packages an application and its dependencies while sharing the host kernel.
Cloud platforms allow infrastructure to be created through software. Instead of physically cabling a new router or switch for every change, administrators can define virtual networks, subnets, routes and security policies through a management platform or API.
A logically isolated network created inside a cloud environment.
IP address ranges used to group workloads within the cloud network.
Software-defined controls can filter traffic between systems or networks.
CCNA expects you to recognise the broad characteristics of common network designs rather than memorise one universal topology.
| Architecture | Idea | Typical use |
|---|---|---|
| Two-tier | Access and collapsed distribution/core layers | Smaller campus networks |
| Three-tier | Access, distribution and core layers | Larger hierarchical campus designs |
| Spine-leaf | Each leaf connects to every spine | Modern data-centre networking |
| WAN | Connects geographically separated networks | Branches, campuses and data centres |
| SOHO | Small-office/home-office network | Small deployments and home networks |
| Cloud | Virtual network resources hosted by a cloud provider | Public, private or hybrid infrastructure |
Connects end devices such as PCs, phones, printers and wireless access points to the network.
Aggregates access switches and can provide routing, policy and redundancy between access and core portions of the network.
Provides high-speed connectivity between major parts of a larger campus network.
In smaller networks, the distribution and core functions may be combined into the same devices.
Traditional campus networks often have traffic flowing from users toward shared services or the Internet. Data centres frequently have large amounts of traffic moving between servers.
A spine-leaf design connects every leaf switch to every spine switch, creating predictable paths between racks or workloads.
Large networks become difficult to manage if every change must be configured manually on each individual device.
Controllers and management platforms can provide a centralised view of network configuration, policy, monitoring and automation.
Define intent or configuration from a central management system.
Apply changes consistently across many devices using software.
Collect operational data centrally for monitoring and troubleshooting.
Imagine a user opens a web application hosted in the cloud.
The user connects through a physical or wireless access network.
Traffic may pass through physical switches, routers and firewalls.
In the cloud, the destination server may actually be a virtual machine or container.
Traffic may cross a virtual switch and a software-defined cloud network before reaching the workload.
Even though some components are virtual, the same fundamental concepts still apply: MAC addresses, IP addresses, routes, ports and security policy.
You've now covered the core ideas behind network models, network devices, Ethernet, IPv4, IPv6, transport protocols, wireless and modern network architecture.
These foundations will keep appearing throughout the rest of CCNA. Next up is Network Access, where we'll get properly hands-on with VLANs, trunks, spanning tree and EtherChannel.
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