CCNA- Switching: VLAN Interview Questions & Answers

What is VLAN?

By default, all ports on a switch are in the same broadcast domain. A Virtual Local Area Network, Virtual LAN, or VLAN, can be used to divide a single broadcast domain to multiple broadcast domains in a layer 2 switched network.


What are the VLAN membership types?

Static VLANs & Dynamic VLANs


What is Static VLAN?

In a static VLAN, the network administrator creates a VLAN and then assigns switch ports to the VLAN. Static VLANs are also called port based VLANs. The association with the VLAN does not change until the administrator changes the port assignment. End-user devices become the members of VLAN based on the physical switch port to which they are connected.

  • Ø The ports on a single switch can be assigned multiple VLANs. Even though two devices are connected to different ports on a same switch, traffic will not pass between them if the connected ports are on different VLANs. We need a layer 3 device (typically a Router) to enable communication between two VLANs.


What is Dynamic VLAN?

In a dynamic VLAN, the switch automatically assigns the port to a VLAN using information from the user device like MAC address, IP address etc. When a device is connected to a switch port the switch queries a database to establish VLAN membership. A network administrator must configure VLAN database of a VLAN Membership Policy Server (VMPS).


What are the types of VLAN connection links?

There are two types of VLAN connection links and they are Access link and Trunk link.

access and trunk linksClick on the Image to see it

The solid lines in above picture are access links and dotted line connecting two switches together is a trunk link. The access links are part of only one VLAN and carry traffic to only the end devices connected to that particular VLAN. But a trunk link is used to connect switches to other switches or to routers and can carry traffic from multiple VLANs.


What is VLAN Frame Tagging?

To identify the VLAN that a frame belongs to, Cisco switches support different identification techniques (VLAN Frame tagging).


What are the different VLAN Frame tagging techniques?

• Inter-Switch Link (ISL): Cisco proprietary VLAN frame tagging. No much support from other vendors. Supported only in old Cisco Switch models.

• IEEE 802.1Q: IEEE industry standards VLAN frame tagging.

• LAN Emulation (LANE): LANE is used to communicate with multiple VLANs over ATM.

• 802.10 (FDDI): Protocol for sending VLAN information over FDDI.


What is Native VLAN?

Normally a Switch port configured as a trunk port send and receive IEEE 801.q VLAN tagged Ethernet frames.

If a switch receives untagged Ethernet frames on its Trunk port, they are forwarded to the VLAN that is configured on the Switch as native VLAN. Both sides of the trunk link must be configured to be in same native VLAN.


What is VTP?

VLAN Trunking Protocol (VTP) is used to communicate VLAN information between switches in the same VTP domain.


What is VTP Domain?

  • Ø A VLAN Trunking Protocol (VTP) domain is one switch or several interconnected switches sharing the same VLAN Trunking Protocol (VTP) environment.
  • Ø A switch can be configured only in one VLAN Trunking Protocol (VTP) domain.
  • Ø Switches in different VTP domains do not share VLAN Trunking Protocol (VTP) information.


What are the VLAN Trunking Protocol (VTP) Modes?

A network switch, which is participating in VLAN Trunking Protocol (VTP), can have three different modes.

• Server Mode

• Client Mode

• Transparent Mode


What is VTP Server Mode?

VLAN Trunking Protocol (VTP) Server mode is the default VTP mode for all Catalyst switches.

At least one Server is required in a VTP domain to propagate VLAN information within the VTP domain.

We can create, add, or delete VLANs of a VTP domain in a Switch which is in VTP Server mode.

The changes made in a switch in server mode are advertised to the entire VTP domain.


What is VTP Client Mode?

VLAN Trunking Protocol (VTP) client mode switches listen to VTP advertisements from other switches and modify their VLAN configurations accordingly.


What is VTP Transparent Mode?

VLAN Trunking Protocol (VTP) transparent mode switches do not participate in the VTP domain, but VTP transparent mode switches can receive and forward VTP advertisements through the configured trunk links.


What is VTP Pruning?

VLAN Trunking Protocol (VTP) pruning is a feature in Cisco switches, which stops VLAN update information traffic from being sent down trunk links if the updates are not needed.



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