VMWare Administrator Interview Questions – Part I

First set of VMware based interview questions..

1. What is Virtualization?
In general it is an act of creating a virtual of something. These can be software, hardware, storage, networking or any other.

2. What are VMware Esx and Esxi? Point out the difference between them?
VMware Esx and Esxi are VMware’s enterprise server virtualization platform. The difference between the two are:
ESXi has no service console which is a modified version of RHEL
ESXi is extremely thin hence results in fast installation and fast boot
ESXi can be purchased as an embedded hypervisor on hardware
ESXi has builtin server health status check

3. What is VMware vSphere? What is vCenter Server?
VMware vSphere is VMware’s cloud computing virtualization platform. It is a software suite consisting of many software components.
VMware vCenter Server is a centralized management application that allows you to manage virtual machines and Esxi hosts centrally.

4. What is promiscuous mode? Where can we find an option to configure this?
Default behaviour of a guest operating system’s virtual network adapter is to receive frames that are meant for it. Enabling promiscuous mode in guest network adapter causes it to detect all frames passed on the virtual switch that are allowed under the VLAN policy for the associated portgroup.
Find promiscuous mode as follows: Configuration tab of Esxi host -> Networking -> Properties of specific vSwitch -> Edit vSwitch or portgroup.
Promiscuous mode is set to Reject by default and it is highly recommended to change this, only when required.

5. Difference between HA and FT
HA

High Availability, minimizes unplanned outage to the protected VM’s.
Configured per cluster.
Works in terms of master and slaves. An election will be held inside the cluster and the host that mounts greatest number of datastores has an advantage of becoming master than others.
Master has got a number of responsibilities as follows:
Monitoring:
State of slave hosts.
Power state of all protected VM’s.
Managing list of cluster hosts and protected VM’s.
Slaves, communicates their health status continuously to master.
Two heartbeat mechanisms: Datastore and Network Heartbeating
Read More here.

FT

Fault Tolerance, avoids unplanned outage to the protected VM’s, enabling higher levels of availability and data protection than HA.
Configured per VM.
Continuous availability for VM’s by maintaining highly available secondary VM (identical to primary).
Each and every actions performed in the primary VM is repeated in the secondary VM, which runs on another host.
Read More here.

6. What are the different types of switches available in VMware? State a major difference between the two.
Standard and Distributed. Standard switches are configured at the host level whereas Distributed switches span across multiple hosts.

7. What is the feature which load balances the burden on Esxi hosts? How it works?
Distributed Resource Scheduler or DRS is this feature. DRS intelligently allocates available resources among the virtual machines. These are carried out as per the rules and policies defined by the users.
Read More here.

8. What feature of VMware enables live migration of virtual machines?
vMotion enables live migration of running VM’s between two Esxi hosts without any downtime. The pre-requisites include:
Host must be licensed for vMotion
Host with at least one vMotion n/w interface (vmkernel port group)
Shared storage(compromised in v5.1)
Same VLAN and VLAN label
GigaBit ethernet network required between hosts
Processor compatibility between hosts
No CD ROM attached and no affinity is enabled
vmware tools should be installed

9. Name some of the common ports used by vCenter?
22 – TCP – Incoming port for SSH server.
53 – UDP – Incoming and Outgoing UDP for DNS Client.
68 – UDP – Incoming and Outgoing UDP for DHCP Client.
80 – TCP – For direct HTTP connections.
88 – TCP – vCenter Single Sign-On Service.
123 – UDP – Outgoing port for NTP client
161 – UDP – Incoming port for SNMP server.
443 – TCP – Default port where vCenter server uses to listen for connections from vSphere client.
902 – TCP/UDP – Default port to send data to managed hosts.

10. What are the different ports used by each vmWare feature such as HA, FT etc?
8042-8045 – TCP/UDP – Incoming port for HA
2050-2250 – TCP/UDP – Outgoing port for HA
8000 – TCP – Incoming and Outgoing port for vMotion
8100,8200 – TCP/UDP – Incoming and Outgoing port for FT
1234,1235 – TCP – Outgoing port for vSphere Replication

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