Unit 5-2: VLAN and Inter-VLAN Routing

What is the main function of the link layer?

Transfers frames between devices over a physical link and provides framing, error detection, and access control.

What is a switch in computer networking?

A Layer 2 device that forwards frames based on MAC addresses, reducing collision domains.

What is a MAC address?

A unique 48-bit hardware address assigned to each network interface card (NIC).

What command displays the MAC address table on a switch?

show mac address-table OR show mac-address-table -> lists MAC addresses learned by the switch and their associated ports.

What is the purpose of the MAC address table?

Used by switches to determine which port to forward a frame out of.

What happens when a switch receives a frame with an unknown destination MAC address?

It floods the frame out all ports except the one it was received on.

What is the process of flooding?

Sending a frame to all ports to find the correct destination when the MAC address is unknown.

What is frame filtering in switching?

A switch forwards frames only to the destination port matching the MAC address in its table.

What is the function of a VLAN?

A Virtual LAN logically separates a single physical network into multiple broadcast domains.

Which command displays VLAN information on a Cisco switch?

show vlan brief - displays all configured VLANs and their associated interfaces.

What is VLAN trunking?

Allows multiple VLANs to traverse a single physical link between switches.

Which command enables trunking on a Cisco interface?

switchport mode trunk - sets the port to permanent trunk mode.

What protocol is used for VLAN tagging on trunk links?

IEEE 802.1Q - inserts a VLAN tag into Ethernet frames to identify VLAN membership.

What is the native VLAN on a Cisco switch?

The VLAN that carries untagged frames on a trunk link (default is VLAN 1).

What command displays trunk status on a switch?

show interfaces trunk - lists all trunk ports and VLANs allowed on each trunk.

What command assigns an interface to a VLAN?

switchport access vlan - assigns a port to a specific access VLAN.

What type of VLAN is assigned manually by the network administrator?

Static VLAN - configured manually on each port.

What type of VLAN assigns devices automatically based on MAC addresses or protocols?

Dynamic VLAN - uses software to assign VLANs automatically.

What is a trunk link?

A link between switches that carries traffic for multiple VLANs using tagging.

What is an access link?

A port that carries traffic for a single VLAN, connecting end devices like PCs.

What is the default VLAN on all Cisco switches?

VLAN 1 - used for management and control traffic unless changed.

What is Inter-VLAN Routing?

A process that allows communication between devices in different VLANs through a router or Layer 3 switch.

What is a router-on-a-stick configuration?

Uses a single router interface configured with multiple subinterfaces for different VLANs.

What command enables a subinterface on a router for VLAN 10?

interface g0/0.10 - creates a subinterface for VLAN 10 traffic.

What command assigns VLAN encapsulation on a subinterface?

encapsulation dot1Q - specifies the VLAN tag for that subinterface.

What command assigns an IP address to a subinterface?

ip address - sets the logical interface's IP address.

What command enables a router interface?

no shutdown - activates the interface.

What is required for inter-VLAN communication to occur?

A Layer 3 device (router or multilayer switch) to route traffic between VLANs.

What is a broadcast domain?

A logical area where all nodes receive broadcast frames from any node within the domain.

What is a collision domain?

A network segment where data packets can collide when being sent simultaneously.

What device reduces collision domains?

A switch - each port creates its own collision domain.

What device reduces broadcast domains?

A router or Layer 3 switch - segments broadcast traffic by subnet or VLAN.

What command shows active interfaces and their assigned VLANs?

show interfaces switchport - displays switchport mode and VLAN membership.

What command verifies trunk configuration?

show interfaces trunk - confirms trunking mode and allowed VLANs.

What is the 802.1Q tag size added to Ethernet frames?

4 bytes - added between the source MAC and EtherType fields.

What VLAN ID range is valid for normal VLANs?

1-1005.

What VLAN ID range is used for extended VLANs?

1006-4094.

What is the maximum number of VLANs supported in 802.1Q?

4094 VLANs.

What command creates a new VLAN?

vlan - adds a new VLAN to the switch configuration.

What command assigns a name to a VLAN?

name - labels the VLAN for easier identification.

What command deletes a VLAN?

no vlan - removes the VLAN from the configuration.

What command saves VLAN configuration permanently?

copy running-config startup-config - ensures VLANs persist after reboot.

What is the default trunk encapsulation method on modern Cisco switches?

802.1Q.

What command sets a port to access mode?

switchport mode access - configures a port to carry traffic for only one VLAN.

What is the difference between access and trunk ports?

Access ports carry traffic for one VLAN; trunk ports carry traffic for multiple VLANs.

What does the show running-config command display?

The current switch or router configuration, including VLAN and interface settings.

What is the purpose of a management VLAN?

Used to remotely manage switches using protocols like SSH or Telnet.

What is trunk encapsulation dot1q used for?

Specifies that 802.1Q tagging is used on trunk links for VLAN identification.

What command shows switch interface status and VLAN assignment summary?

show interfaces status - displays port status, VLAN, and duplex/speed info.

What is the main benefit of VLANs?

Improve network performance and security by segmenting broadcast traffic.

What is a Layer 2 broadcast frame?

A frame sent to all devices within the same VLAN or broadcast domain.

What is the main purpose of using switches instead of hubs?

Switches eliminate collisions and improve network efficiency by using MAC-based forwarding.

What command tests VLAN connectivity?

ping - verifies communication between devices in the same or different VLANs.

What command displays brief VLAN mapping?

show vlan brief - quick summary of VLAN IDs and port assignments.