VDC - [Part 2] - INTERVIEW QUESTIONS

Question - 1 Explain the Control Plane in VDC ? 

• When VDC is created, Nexus OS software will replicate Control plane processes to all other VDC. 
• This replication allow to VDC administrators to use VLAN and VRF independently in other VDCs. 
• In the Ethernet VDC, same VLANs numbers can be used in different VDC.

Question - 2 Interface allocation in VDC.

• When Nexus 7K Series switch is booted first, then, in the modular switch platform all interfaces of all line cards are placed in the default VDC - VDC 1. 
• So by default, all the physical interfaces belong to Default VDC.
• An interface can only belong to one VDC.
• If you will create a new VDC in N7K, then you need to manually assign physical interfaces to it.
• If you will move the interface from default VDC to New VDC, then all the configuration will be erased under this interface.
• If we are not able to assign any interface to VDC or interfaces are automatically assigned then it is due to port grouping.
• All the interfaces, which belong to the same port group will be added to the VDC automatically, when you will assign a single interface.
• Interfaces of different line cards can be assigned to different VDCs.  
• In Nexus, all ports on the same hardware ASIC must be in same VDC as they are on the same hardware asic.
• If an interface will be placed into a VDC, then this interface will not be managed by default VDC context.

Questions - 3 What are limitations of VDC ?

• Only Nexus 7K (7000, 7700) series platform support the VDC
• VDCs will not share the interfaces, VLANs, VRF tables, or port channels.
• Only users can create VDCs who has the network Admin role.
• Only users who has network-admin or network-operator role can use the ‘switchto vdc’ command.
• User cannot grant permission to another role to use the ‘switchto vdc’ command.
• When a network-admin will use the ‘switchto vdc’ command, then this user will become a vdc-admin for the new VDC. Any other roles with the user will not be valid after the switchto vdc command.
• When a network-operator will use the ‘switchto vdc’ command, then this user will become a vdc-operator for the new VDC. Any other roles with the user will not be valid after the switchto vdc command.
• When a network-admin or network-operator will use the ‘switchto vdc’ command, then this user cannot use this command to switch to another VDC. There is only one option is to use the command ‘switchback vdc’ to return to the original VDC.
• The maximum number of port-channels across N7K for all VDCs is 768.
• Number of the VDC per nexus switch depends on the supervisor model.

1. SUP1 module - 4 non-default VDC and one admin VDC. OR 3 non-default VDC and 1 default VDC
2. SUP2 module - 1 admin VDC and 4 non-default VDCs.
3. SUP2E module - 1 admin VDC and 8 non-default VDCs
4. SUP3E module - 8+1 admin VDC

Question - 4 Licensing Requirements for VDCs.

• If you want to create aVDC, then you will required an advanced license. Without license only default VDC will be available, you cannot create other VDC
• Without a license, if you will enable the default VDC as an admin VDC, then you can only enable one nondefault VDC
• The storage VDC is enabled by using the storage license, which will be associated with a specific line card.
• There are 120-day grace period available so you can try this feature for 120 days, if the grace period expires, then any nondefault VDCs will be removed from the switch configuration.

Question - 5 VDC deployment scenarios ?

You can use VDC in below Deployment Scenarios.

• Migration Scenarios of Data Center
• To create a redundant core and aggregation layer.
• To create separate environments for test and production.
• To create different organizations on the same physical switch.
• To create Separate application environments.

Question - 6 Explain Fault Isolation in VDC ?

• VDC provides fault isolation facility. Each VDC uses its own control plane, data plane, and management plane. If any issue will occurs in any L2 or L3 process, then it will not be affect any other processes, which is running on other logical switches.
• If control plane will fail in one VDC , then it will not be affect the control plane of other VDCs.
• VLAN number and VRF names can be reused in different VDC.
• There will be no internal communication between different VDC.
• To forward the traffic from one VDC to another VDC, will need A separate connection.

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Anubhav Upadhyay

Hello and welcome to networktopic Blog. My name is Anubhav. I am a Senior Network Egineer. I have created this blog specially to serve interview questions and answer on Network Routing and Switching, I will try my best to serve correct and updated networking knowledge for you as per my corporate experience.

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