Cisco Nexus Interview Q & A

If you are Planning for DataCenter Job Interview then this article can surely help with cisco nexus frequently asked questions and answers -
                                                                                                                           
Question 1 –What is VDC ?

Answer:-

VDC  - Virtual Device Context
Cisco Nexus Switches Feature.
Allows to divide a Nexus Chassis into multiple virtual chassis known as VDC.
Each VDC means a different Switch.
By default we have entire chassis is known as Default VDC or Admin VDC whereas the created VDCs are known as Non-Default / Non – Admin / Member VDCs.
Creation and Deletion of VDCs can be only done from Admin VDC.
By using command – “ show vdc “ we can view all the vdc created .
                                                                                                                           
Question 2 –How Many VDC can be configured in Nexus 7K Switches?

Answer:-

Number of VDC configured depends upon the Supervisor engine.
Sup 1 – Maximum 4 VDCs
Sup 2 – Maximum 4+1 VDCs (including admin VDCs)
Sup 2E – Maximum 8+1 VDCs (including admin  VDCs)

                                                                                                                           
Question 3 –Tell something about Licenses & Host ID in Nexus Switches? 

Answer:-

In NX-OS Licenses are required to use features and features –set.
For e.g if you need to run BGP then you must enable feature BGP on your nexus box.
Licenses are generated using Host –ID which is unique for each nexus box.
Hence we can’t use License of one Host-ID in another.
#show license Host-ID - to find unique Host ID .

                                                                                                                           
Question 4 –What are the Spanning Tree Modes available on Nexus 7K and 5K?

Answer:-

NX-OS only supports 2 STP Modes .
RPVST +   Rapid Per Vlan Spanning Tree +
MST  Multiple Spanning Tree
                                                                                                                           
Question 5 –What is vPC in Nexus Devices?

Answer:-

VPC (Virtual Port Channel) is a feature on the Cisco Nexus switches that provides the ability to configure a Port-Channel across multiple switches which is not possible in traditional Port-Channel.
Hence it is also know as Multichassis EtherChannel (MEC)                                                                                                                                                                                                       
Question 6 –How to verify features enabled on Nexus Devices ?

Answer:-

“show feature”
N7K# show feature
 Feature Name Instance State
      -------------------- -------- --------
       bgp            1  enabled
       scheduler 1 enabled
       isis             2 disabled
       ospf           1 enabled

                                                                                                                 
Question 7 –How to enable Grace Period for the expired License in Nexus Devices ?

Answer:-

We can enable the Grace Period by entering into configuration mode and use command –
    “license grace-period”.
(config)#license grace-period
                                                                                                                           
Question 8 –What are the differences between VPC and VSS ?

Answer:-

Both VPC & VSS are used to create multi chasis etherchannel.
VPC is Cisco Nexus specific whereas VSS is created using Cisco 6500 switches.
In VPC there is different control plane for each switch and in VSS the control plane will be common for both the switches.
VPC supports LACP only whereas VSS supports both LACP and Pagp.
Using VPC can support only L2 port channels across multichassis whereas VSS can support  L3 port channels.

                                                                                                                           
Question 9 – What is FEX ?

Answer:-

FEX – Fabric Extender.
FEX are brainless devices which does not have its own control  plane.
These are Nexus 2000 series switches which are connected and managed by Parent Switch. (Parent switches are mostly Nexus 5000 series switches)
On FEX  Fabric Ports are connected to Parent Switch and Front Panel ports are used for the downlinks connections where Servers are connected.
FEX feature can be enabled by using command “feature fex”.

                                                                                                                           
Question 10 –What are the types of images that run on an Nexus Switch?

Answer:-

There are 3 types of NX-OS images that runs on an Nexus Switches.
Kickstart  –This is the Kernel image
System – This is the actual image which run on top of kernel.
EPLD - Cisco releases EPLD image upgrades to enhance hardware functionality –upgrading the modules  or to resolve known issues.

Thanks for Reading !!!!!

Best of luck