Section 2. Introducing Local-Area Networks Flashcards
Q1-What are local-area networks?
Local-area networks (LAN) are high-speed, low-error data networks that cover a small geographic area. LANs are usually located in a building or campus and do not cover a large distance. They are relatively inexpensive to develop and maintain. LANs connect computers, printers, and other devices in a single building or a limited area.
Q2-What are LAN standards?
LAN standards define the physical media and connectors used to connect to the media at the physical layer and the way devices communicate at the data link layer. LAN standards encompass Layers 1 and 2 of the OSI model. An example of a LAN standard is Ethernet, which is also known as 802.3.
Q3-What are the typical components found in LANs?
Typical components found in LANs are Computers: PCs, servers, tablets Interconnections: NICs, media Network devices: Switches, routers, access points Protocols: Ethernet, IP, ARP, DHCP
Q4-What is the logical topology of Ethernet?
Bus. Ethernet uses a logical bus topology and either a physical bus or star topology.
Q5-What are two types of Layer 1 network devices?
Two types of Layer 1 network devices are as follows: Repeaters: Regenerate and retime network signals, allowing the signal to travel a longer distance on a network media. Hubs: Known as a multiple-port repeaters, hubs also regenerate and retime network signals. The main difference between a hub and a repeater is the number of ports a hub has. A repeater typically has two ports, whereas a hub has from 4 to 48 ports.
Q6-What are some network devices that operate at the data link layer (Layer 2)?
Bridges and switches are network devices that operate at the data link layer. Both devices make decisions about what traffic to forward, flood, or drop (filter) by MAC addresses, and logical network addresses are not used at this layer. Data link layer devices assume a flat address space. Typically, a bridge is designed to create two or more LAN segments and is software implemented. A switch is a hardware version of a bridge, has many more ports than a bridge, and is designed to replace a hub while providing the filtering benefits of a bridge.
Q7-What is a LAN segment?
A LAN segment is a network connection made by a single unbroken network cable. Segments are limited by physical distance because, after a certain distance, the data transmission becomes degraded because of line noise and the reduction of signal strength.
Q8-What devices can you use to extend a LAN segment?
To extend a LAN segment, you can use the following devices: Hubs Repeaters Bridges Switches
Q9-How do collisions occur on an Ethernet LAN?
Collisions occur on a shared LAN segment when two devices try to communicate at the same time. In a shared Ethernet segment, only one device can transmit on the cable at a time. When two devices try to transmit at the same time, a collision occurs. When a collision occurs, a jam signal is sent from a workstation. A collision affects all the machines on the segment, not just the two that collided; when the jam signal is on the wire, no workstations can transmit data. The more collisions that occur in a network, the slower it will be, because the devices must resend the packets that collided.
Q10-What are collision domains?
A collision domain is set of LAN interfaces whose frames could collide with each other. For example, all devices connected to a hub are in the same collision domain.
Q11-What happens when you segment the network with hubs/repeaters?
Hubs and repeaters operate at the physical layer of the OSI model; segmenting a network with these devices appears as an extension to the physical cable. Hubs and repeaters are transparent to devices; they are unintelligent devices. All devices that connect to a hub/repeater share the same bandwidth. Hubs/repeaters create a single broadcast and collision domain.
Q12-What is the advantage of segmenting a LAN with switches?
Switches operate at Layer 2 of the OSI model and filter and forward by MAC address. Each port on a switch provides fully dedicated bandwidth and creates a single collision domain. Because switches operate at Layer 2 of the OSI model, they cannot filter broadcasts, and they create a single broadcast domain.
Q13-What devices are used to break up collision domains?
Switches, bridges, and routers are used to break up collision domains. They create more collision domains and result in fewer network collisions. Each port on a bridge, switch, and router creates one collision domain. For example, if you have a switch with 24 ports, you have 24 separate collision domains.
Q14-In an attempt to extend your Ethernet LAN segment, you add a 24-port hub. How many collision domains will you have in the segment with the addition of the hub?
You will have one collision domain. A hub only extends the Ethernet segment, and all devices share the same segment bandwidth. As a result, a hub does not create more collision domains.
Q15-In an attempt to extend your Ethernet LAN segment, you add a 24-port switch. How many collision and broadcast domains will you have in the segment with the addition of a switch?
You will have 24 collision domains and one broadcast domain. Switches operate at Layer 2 of the OSI model, and they divide the network into different segments, thus creating more collision domains. Each port on a switch creates one collision domain. Also, because a switch operates at Layer 2 of the OSI model, it cannot filter broadcasts. As such, a switched network will have one broadcast domain.
Q16-What are broadcast domains?
A broadcast domain defines a group of devices that receive each other’s broadcast messages. As with collisions, the more broadcasts that occur on the network, the slower the network will be. This is because every device that receives a broadcast must process it to see whether the broadcast is intended for that device.
Q17-You install a six-port router on your network. How many collision domains and broadcast domains will be created on the network with the addition of the six-port router?
Six collision domains and six broadcast domains will be created. Each interface on a router creates a collision domain and a broadcast domain.
Q18-What is a broadcast storm?
Broadcast storms occur when many broadcasts are sent simultaneously across all network segments. They are usually caused by Layer 2 loops because of spanning tree misconfigurations, a bad network interface card (NIC), a faulty network device, or a virus.
Q19-What three primary functions do Layer 2 switches provide?
The three primary functions that Layer 2 switches provide are as follows: MAC address learning Frame forwarding/filtering Loop avoidance with the Spanning Tree Protocol
Q20-How does a switch differ from a hub?
Switches are Layer 2 devices and make forwarding decisions based on Layer 2 information. Hubs operate on Layer 1. Switches make forwarding decisions based on Layer 2 information by learning MAC addresses on incoming frames and storing these frames in a MAC address table.
Q21-A fundamental concept behind LAN switching is that it provides microsegmentation. What is microsegmentation?
Microsegmentation is a network design (functionality) where each workstation or device on a network gets its own dedicated segment (collision domain) to the switch. Each network device gets the full bandwidth of the segment and does not have to contend or share the segment with other devices. Microsegmentation reduces collisions because each segment is its own collision domain.
Q22-What advantages are offered by LAN segmentation using LAN switches?
A switch considers each LAN port to be an individual segment. The advantages offered by LAN segmentation using LAN switches are as follows: Collision-free domains from one larger collision domain Efficient use of bandwidth with full duplex Low latency and high frame-forwarding rates at each interface port
Q23-What are the three switching methods (frame transmission modes) in Cisco Catalyst switches?
The three frame operating modes to handle frame switching are as follows: Store-and-forward Cut-through Fragment-free
Q24-What is the Cisco Catalyst store-and-forward switching method?
In the store-and-forward switching method, the switch’s incoming interface receives the entire frame before it forwards it. The switch compares the last field in the datagram, the cyclic redundancy check (CRC), against its own frame check sequence (FCS) calculations to make sure that the frame is free from physical and data-link errors. If the switch observes any errors in the FCS calculations, the frame is dropped. If the frame is a runt (less than 64 bytes, including the CRC) or a giant (more than 1518 bytes, including the CRC), the switch discards it. Because the switch stores the frame before forwarding it, latency is introduced in the switch. Latency through the switch varies with the size of the frame.
Q25-What is the Cisco Catalyst cut-through switching method?
In cut-through switching mode, the switch only checks the frame’s destination address and immediately begins forwarding the frame out the appropriate port. Because the switch checks the destination address in only the header and not the entire frame, the switch forwards a frame that has a bad CRC calculation.
Q26-What is the Cisco Catalyst fragment-free switching method?
Also known as modified cut-through, fragment-free switching checks the first 64 bytes of the frame before forwarding the frame. If the frame is less than 64 bytes, the switch discards the frame. Ethernet specifications state that collisions should be detected during the first 64 bytes of the frame. By reading the first 64 bytes of the frame, the switch can filter most collisions, although late collisions are still possible.
Q27-What are six ways to configure a Cisco device?
Six ways to configure a Cisco device are as follows: Console connection Auxiliary connection (through a modem) Telnet connection HTTP/HTTPS connection Secure Shell (SSH) Connection Cisco Prime
Q28-What type of cable do you need to connect to a Cisco device’s console port?
You need an RJ-45–to–RJ-45 rollover cable. A rollover cable is a cable that has each pin wired to its opposite number at the other end.
Q29-What are the console configuration settings needed to connect to a Cisco device’s console port?
The COM port configuration settings needed to connect to a Cisco device’s console port are as follows: Speed: 9600 bits per second Data bits: 8 Parity: None Stop bit: 1 Flow control: None
