Network Devices

Question 1

Hubs

Answer 1

• A hub is a multiport physical repeater used to connect end-user workstations.
• Incoming frames received on any hub port are rebroadcast to all other ports except the one where the frame arrived.
• Hubs are inexpensive but do not create separate broadcast or collision domains.

Question 2

Collision Domains

Answer 2

• A collision domain is a network segment where collisions can occur.
• If multiple devices share a hub, they all use the same bandwidth, leading to potential collisions.
• For example, if four computers are connected to a hub, collisions can happen when frames are sent simultaneously.
• Hubs do not make forwarding decisions based on MAC or IP addresses.

Question 3

CSMA/CD and Half-Duplex

Answer 3

• Ethernet devices connected to hubs rely on Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
• CSMA/CD ensures that devices listen before transmitting data.
• If no transmissions are detected, a device sends its data; if a collision occurs, devices wait before retransmitting.
• Hubs operate in half-duplex mode, meaning devices cannot transmit and receive simultaneously.

Question 4

Bridges

Answer 4

• A bridge connects endpoint devices in a network.
• It uses MAC addresses to deliver frames.
• Bridges maintain a forwarding database with attached hosts’ MAC addresses.

Question 5

Bridge Forwarding Process

Answer 5

• When a packet arrives, the sender’s MAC address is recorded.
• If the recipient’s address is known, the packet is sent directly.
• Otherwise, the packet is flooded to all ports (except the arrival port).
• Hosts use MAC addresses to determine if the data is intended for them.

Question 6

Bridge Collision Domains

Answer 6

• Each bridge port creates a separate collision domain.
• Bridges help increase collision domain segmentation.

Question 7

Bridge Broadcast Domains

Answer 7

• Bridges do not create separate broadcast domains.
• All devices connected to a bridge share the same broadcast domain.

Question 8

Switch Basics

Answer 8

• Like bridges, switches provide network connectivity to endpoint devices.
• Switches operate at Layer 2 or Layer 3.
• Layer 2 switches function similarly to bridges, while Layer 3 switches add routing functionality.

Question 9

Switch Forwarding Operation

Answer 9

• A switch uses data packet headers to forward packets to correct ports.
• This reduces collisions, improves traffic flow, and enhances performance.
• Switches break large networks into smaller segments.
• Microsegmentation creates dedicated network segments for each switch port.

Question 10

Layer 2 Switches (MAC)

Answer 10

• Layer 2 switches use MAC addresses for switching frames.
• Known MAC addresses are stored in the Content Addressable Memory (CAM) table.
• The table associates MAC addresses with physical interfaces.
• MAC addresses are dynamically learned as the switch forwards traffic.

Question 11

Switch Broadcast and Collision Domains

Answer 11

• Each computer connected to a switch has its own collision domain.
• Layer 2 switches forward broadcasts, creating a single broadcast domain.
• VLANs can separate broadcast domains within Layer 2 switches.
• Layer 3 switches have integrated routing capabilities and enable direct VLAN communication.

Question 12

Router Functionality

Answer 12

• Routers forward packets between computer networks.
• Unlike switches, routers create separate broadcast domains.
• Devices connected to a router reside in separate broadcast domains.
• Broadcasts sent on one network segment attached to the router won’t be forwarded to other segments.

Question 13

Path Decisions and Routing Tables:

Answer 13

• Routers make path decisions based on logical addresses (like IP addresses).
• IP address information is stored in a routing table.
• The routing table is stored in a Ternary CAM (TCAM) memory section.
• TCAM tables allow nonexact matches for queries (unlike Layer 2 switch CAM tables).
• Routers use TCAM tables for ACL rules, QoS policies, and routing table lookups.

Question 14

Router Packet Forwarding

Answer 14

• When a router receives a packet, it forwards it based on the routing table.
• If a packet is destined for an unknown remote network, it’s dropped.
• No static default route or gateway of last resort: ICMP Destination Unreachable error is sent.