Virtualization

What this chapter covers

Virtualization is about running many logical devices or networks on shared physical equipment.

The chapter looks at three levels.

The first is the server, where hypervisors and virtual switches host many machines. The second is the router, where VRFs and tunnels keep traffic separate and secure. The third is the network as a whole, where overlay technologies build virtual networks on top of a routed base.

The chapter follows the Virtualization domain of the CCNP 350-401 ENCOR outline. It has three outline topics, spread across four pages.

How the topics fit together

Each page isolates something from something else, at a different level.

• Hypervisors share server hardware among virtual machines, and a virtual switch links them to the LAN.
• VRFs split one router into several separate routing tables.
• GRE and IPsec carry that separated traffic across a shared network, with encryption when needed.
• LISP and VXLAN build whole virtual networks that ride over an IP underlay.

The same pattern repeats in all of them. A physical resource is shared, a logical boundary keeps users apart, and an extra header or table does the separating.

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.

The VRF and tunnel pages include configuration, so build them in a lab or simulator and check each step with the show commands. The hypervisor and overlay pages are mostly about vocabulary and roles, so make short flash cards for terms such as EID, RLOC, VNI and VTEP.