ACSP VLANs, Spanning Tree Protocol & Layer 2 Technologies — Questions and Answers

Question 1: What is the primary function of VLANs?

Segmentation of the network
Encryption of data
Configuration of IP addresses
Routing between different networks

VLANs (Virtual Local Area Networks) are used to logically segment a single physical network into multiple broadcast domains. This primary function allows administrators to group devices based on function, department, or application, regardless of their physical location. Network segmentation improves security by isolating traffic and reduces the size of broadcast domains, enhancing network efficiency.

Question 2: What does the Spanning Tree Protocol (STP) prevent?

Network congestion
Data loss
Routing failures
Bridge loops

The Spanning Tree Protocol (STP) is a Layer 2 network protocol designed to prevent bridge loops in Ethernet networks. In redundant network topologies, where multiple paths exist between switches, loops can cause broadcast storms and MAC address table instability. STP works by intelligently blocking redundant paths, ensuring there is only one active path between any two network segments while still providing redundancy in case of a link failure.

Question 3: Which layer does Spanning Tree Protocol operate on?

Layer 1
Layer 2
Layer 3
Layer 4

The Spanning Tree Protocol (STP) operates at Layer 2 of the OSI model, which is the Data Link Layer. This layer is responsible for node-to-node data transfer and error detection. STP functions by exchanging Bridge Protocol Data Units (BPDUs) between switches to determine the network topology and block redundant paths, all based on MAC addresses and switch port states, not IP addresses.

Question 4: What is a key benefit of using VLANs in a network?

Increased routing efficiency
Improved bandwidth
Enhanced security
Faster network speeds

A key benefit of using VLANs in a network is enhanced security. By segmenting the network into separate broadcast domains, VLANs isolate traffic between different user groups or device types. This prevents unauthorized access to sensitive resources and contains security breaches within a specific VLAN, limiting their impact on the entire network.

Question 5: How does STP determine the root bridge?

Highest MAC address
Lowest IP address
Lowest Bridge ID
Highest IP address

STP determines the root bridge by comparing the Bridge ID (BID) of all switches in the network. The Bridge ID is a combination of a configurable bridge priority (defaulting to 32768) and the switch's MAC address. The switch with the lowest Bridge ID is elected as the root bridge, serving as the central reference point for all Spanning Tree calculations.

Question 6: Which VLAN type can be used to segment voice traffic?

VLAN 1
VLAN 10
VLAN 20
VLAN 50

Any dedicated VLAN can be used to segment voice traffic, as the choice of VLAN ID is an administrative decision. However, it is common practice to assign a specific, non-default VLAN (like VLAN 50 in this example) for voice traffic to enable Quality of Service (QoS) prioritization and easier management. This ensures voice calls receive preferential treatment and maintain high quality, separate from other data traffic.

Question 7: Which protocol does STP use to exchange information about network topology?

ICMP
BPDU
IGMP
ARP

STP uses Bridge Protocol Data Units (BPDUs) to exchange information about the network topology between switches. These special data frames contain details such as the root bridge ID, the cost to reach the root, and the sending switch's own BID. By exchanging BPDUs, switches can collectively determine the optimal network topology and identify which ports should be blocked to prevent loops.

Question 8: What is the main purpose of Layer 2 switches in a VLAN?

To route traffic between VLANs
To filter traffic based on IP
To forward traffic using MAC addresses
To connect multiple subnets

The main purpose of Layer 2 switches in a VLAN is to forward traffic within the same VLAN using MAC addresses. Layer 2 switches operate at the data link layer and learn MAC addresses of connected devices to make forwarding decisions. They do not route traffic between different VLANs; that function requires a Layer 3 device, such as a router or a Layer 3 switch.

Question 9: What is the default priority of a root bridge in Spanning Tree Protocol?

0
128
32768
65536

The default priority of a root bridge in Spanning Tree Protocol is 32768. This value is part of the Bridge ID (BID), which also includes the switch's MAC address. When electing the root bridge, the switch with the lowest BID is chosen. Network administrators can manually configure a lower priority value (in increments of 4096) to influence which switch becomes the root bridge.

ACSP VLANs, Spanning Tree Protocol & Layer 2 Technologies

What is the primary function of VLANs?