Architecture

What this chapter covers

Architecture explains how a service provider network is built, what it runs on, and how it is protected.

It starts with the big designs: Metro Ethernet, MPLS, unified MPLS, segment routing and SRv6. It then looks at the access and transport technologies around the core, and at the mobile network that rides on it.

The chapter also compares the Cisco operating systems and explains how providers virtualise network functions. It ends with QoS models and the three planes of security.

How the topics fit together

The pages move from the shape of the network, to the software inside it, to the rules that keep it fair and safe.

The topics build on each other in this way:

• Core architectures describe how packets find a path across the provider network.
• Transport and mobility describe how customers, radios and optical links connect to that core.
• Software and virtualization describe the operating systems and the software based network functions.
• QoS architecture describes how traffic is marked, trusted and treated across the core.
• Security protects the control plane, the management plane and the data plane.

How to use these pages

Each topic page has the same shape, so you can skim for what you need.

• What it is: the idea in plain words.
• How it works: the mechanism, with diagrams and example commands.
• What to remember for the exam: the facts to memorise.
• Common mistakes: the classic traps.
• Check yourself: three questions to test your understanding.

Many commands are shown for IOS XR, because it is the main provider platform. Where IOS XE differs, the page says so. Read the console blocks closely, because the two platforms use different command words for the same job.