2.1 Describe device virtualization technologies

What this section tests

Section 2.1 is a describe topic. The exam wants you to explain how one physical server runs many logical devices, and where the network path crosses into the server.

Learn one traffic path, not three isolated definitions:

• The hypervisor divides hardware into usable parts.
• The virtual machine uses those parts as CPU, memory, disk, and NICs.
• The virtual switch connects the virtual NICs to each other and to the physical network.

For each part, name the control point and the proof:

• Control point: the hypervisor and its port group policy decide what a VM can reach.
• Boundary: the virtual switch is where forwarding moves from software to hardware.
• Proof: the VM MAC address in the physical switch MAC table shows the full path works.

The traffic path

Think of a virtual router named R1 on a server.

R1 virtual NIC
-> virtual switch / port group
-> physical host NIC (uplink)
-> physical switchport
-> enterprise network

A packet from R1 passes through the virtual switch before it reaches the wire. The virtual switch can apply a VLAN tag, a security policy, or a teaming policy before the packet leaves the host.

If the path breaks, check each point in order:

1. Is the VM NIC connected?
2. Is the VM on the correct port group?
3. Is the VLAN or trunk correct?
4. Is the host uplink up?
5. Does the physical switchport allow the VLAN?
6. Is the gateway reachable?

Child articles

• 2.1.a Hypervisors Type 1 and Type 2: bare metal vs hosted, and how each model changes troubleshooting.
• 2.1.b Virtual Machines: guest OS, virtual NICs, and lab networking modes.
• 2.1.c Virtual Switching: port groups, VLAN tagging, trunks, and host uplinks.

High-yield comparison

Why network engineers care

Virtualization moves part of the network inside the server. A network problem can exist where the physical switch cannot see it.

A VLAN can be correct on the physical switch but wrong on the port group. A VM can have the correct IP address and sit on the wrong virtual network. A trunk can allow VLAN 20 while the virtual switch presents VLAN 10 to the VM.

You do not need to administer every hypervisor. You need to know where a packet can be tagged, filtered, or dropped inside the host.

Lab: map a VM packet

Topology:

VM-A eth0 -> vSwitch / port group USERS-VLAN20 -> Host NIC vmnic0 -> SW1 Gi1/0/10 -> R1 gateway 10.20.20.1

Physical switchport:

interface GigabitEthernet1/0/10
 description Hypervisor-Host-01-Uplink
 switchport mode trunk
 switchport trunk allowed vlan 20,30
 spanning-tree portfast trunk

Do these steps:

1. Name the control point for the VLAN that VM-A uses. (Answer: the port group USERS-VLAN20.)
2. Name the boundary between software switching and hardware switching. (Answer: the host uplink vmnic0.)
3. Name the command on SW1 that proves VM-A traffic arrives. (Answer: show mac address-table interface gi1/0/10.)
4. Name the first thing to check inside VM-A. (Answer: its IP address and default gateway.)

Exam traps

• A virtual switch is still a switch. It forwards frames between vNICs and uplinks.
• Type 1 vs Type 2 describes where the hypervisor runs, not VM quality.
• A VM is not a container. A VM runs a guest OS on virtual hardware.
• Port group VLAN settings and physical trunk settings must agree.
• The physical switch sees traffic after the virtual switch already made decisions.

Pass check

You are ready for Section 2.1 when you can do these things:

• Draw the path from a VM vNIC to the physical network.
• Explain the difference between Type 1 and Type 2 hypervisors.
• Name the role of a port group in the traffic path.
• Say whether a failure is inside the VM, in the virtual switch, on the uplink, or in the physical network.