Hello Guys, myself Bipul Roy, I am dual CCIE (CCIE#36690). Find below the list of interview questions on VLAN and these are the most common questions asked by the interviewer. I hope this will help you to prepare the networking interview. Best of luck and Thank you.
1. What is VLAN?
VLAN logically creates multiple broadcast domains in a single physical LAN. Or VLAN is used to break up a broadcast domain on a switch network.
2. What are the advantages of using VLAN?
- Reduce the CPU load on each device by reducing the number of devices in a broadcast domain.
- Reduce security risk by reducing the number of devices in a broadcast domain to receive flooded frames (broadcast, multicast, unknown unicast) by the switch.
- Improve security by separating hosts by different broadcast domains.
- Provide flexible design by department or group wise.
- To isolate and solve problems quickly.
3. What is a Native VLAN?
- Native VLAN works on the Trunk link and only supported 802.1q trunking encapsulation. In 802.1Q trunking encapsulation, native VLAN frames travel over the trunk port and do not carry VLAN ID information. It just travels without a VLAN tag.
- VLAN 1 is default Native VLAN, but we can change it.
- ISL trunking does not support native VLAN.
4. Why VLAN 1 is default Native VLAN?
By default in a new switch, there is only one VLAN, which is VLAN 1. So, VLAN 1 is kept as Native VLAN by default.
5. What is the normal and extended range of VLANs?
- Normal range VLAN 1 – 1005.
- Extended range VLAN 1006 – 4094.
6. What are default and reserved VLANs?
- VLAN 1, 1002-1005 are default VLANs.
- VLAN 0 and VLAN 4095 are reserved.
7. What is Access and Trunk Link?
- The link on which an end-user is connected is called access link.
- The link on which another switch is connected is called the trunk link.
8. Why do we need trunking?
When multiple VLAN communication is required over the Switch to Switch link, then we configure inter-switch links as Trunk.
9. What are Trunking encapsulation protocols?
- 802.1q or dot1q – which is IEEE standard
- ISL or Inter-Switch Link – which is Cisco proprietary
10. What is DTP? What are the different modes of DTP?
- DTP is Dynamic Trunking Protocol, try to form a trunk link with negotiation between two switches. It is Cisco proprietary.
- DTP modes are Dynamic Desirable and Dynamic Auto
11. Why do we need the same Native VLAN in every switch of a Layer 2 Network?
If the Native VLAN is not the same in every switch in a layer 2 network then a Native VLAN of one switch can communicate with Native VLAN of different switches easily as their frames remain untagged over a trunk link.
12. What is the different methods to create VLAN in a switch?
- We can create VLAN from the global configuration mode.
- We can create VLAN by assigning VLAN on an interface sub-configuration mode.
- We can create VLAN from the VLAN database mode.
13. What is the purpose of VLAN 0 and 4095?
- VLAN 0 is used for priority traffic inside the switch IOS.
- VLAN 4095 is used by IOS for its internal use.
14. What is a management VLAN?
The VLAN through which a switch is accessed for management purpose or the VLAN which holds the management IP address for remote access.
15. What is the use of VLAN ID 1002 to 1005?
These four VLAN IDs are used for FDDI and Token Ring technology.
16. What are the commands to check the VLAN database?
- show VLAN
- show VLAN brief
- show VLAN id <VLAN_ID>
17. How to disable a VLAN ID?
Under VLAN configuration mode, type the command “shutdown”.
18. Can we assign multiple VLAN IDs on an access port?
No, we can assign only a single VLAN ID on an access port.
19. How many VLAN IDs we can assign on an Access Port?
One Data VLAN and one Voice VLAN.
20. How many bits are used for VLAN ID?
21. How many VLANs are allowed by default on a Trunk port?
22. What is the use of Native VLAN?
Native VLAN works on Trunk Port. Any untagged frame comes on the Trunk port that frame will be tagged with Native VLAN for communication.
23. How many VLAN ID we can create on a Switch?
It will depend on the Switch model or hardware capacity. Cisco small catalyst L2 or L3 switches only support 255 VLANs and Multilayer switches support 4094 VLANs.
24. Where Switches save VLAN ID?
Inside vlan.dat file and this file stores in Flash Memory.
25. Can we configure extended-range VLAN in small Cisco L2 or L3 switches?
No, these type of switches by default operates in VTP server mode. For extended VLAN creation switch to be on VTP transparent mode.
You can get here Best CCNA Interview Questions on Device Management and Basic Routing