Chapter 2 Fundamentals of Ethernet LANs Flashcards
- In the LAN for a small office, some user devices connect to the LAN using a cable, while others connect using wireless technology (and no cable). Which of the follow- ing is true regarding the use of Ethernet in this LAN?
a. Only the devices that use cables are using Ethernet.
b. Only the devices that use wireless are using Ethernet.
c. Both the devices using cables and those using wireless are using Ethernet.
d. None of the devices are using Ethernet.
a. Only the devices that use cables are using Ethernet.
- Which of the following Ethernet standards defines Gigabit Ethernet over UTP cabling?
a. 10GBASE-T
b. 100BASE-T
c. 1000BASE-T
d. None of the other answers is correct.
c. 1000BASE-T
- Which of the following is true about Ethernet crossover cables for Fast Ethernet?
a. Pins 1 and 2 are reversed on the other end of the cable.
b. Pins 1 and 2 on one end of the cable connect to pins 3 and 6 on the other end of the cable.
c. Pins 1 and 2 on one end of the cable connect to pins 3 and 4 on the other end of the cable.
d. The cable can be up to 1000 meters long to cross over between buildings.
e. None of the other answers is correct.
b. Pins 1 and 2 on one end of the cable connect to pins 3 and 6 on the other end of the cable.
- Each answer lists two types of devices used in a 100BASE-T network. If these devices were connected with UTP Ethernet cables, which pairs of devices would require a straight-through cable? (Choose three answers.)
a. PC and router
b. PC and switch
c. Hub and switch
d. Router and hub
e. Wireless access point (Ethernet port) and switch
b. PC and switch
d. Router and hub
e. Wireless access point (Ethernet port) and switch
- Which of the following is true about the CSMA/CD algorithm?
a. The algorithm never allows collisions to occur.
b. Collisions can happen, but the algorithm defines how the computers should notice a collision and how to recover.
c. The algorithm works with only two devices on the same Ethernet.
d. None of the other answers is correct.
b. Collisions can happen, but the algorithm defines how the computers should notice a collision and how to recover.
- Which of the following is true about the Ethernet FCS field?
a. Ethernet uses FCS for error recovery.
b. It is 2 bytes long.
c. It resides in the Ethernet trailer, not the Ethernet header.
d. It is used for encryption.
c. It resides in the Ethernet trailer, not the Ethernet header.
- Which of the following are true about the format of Ethernet addresses? (Choose three answers.)
a. Each manufacturer puts a unique OUI code into the first 2 bytes of the address.
b. Each manufacturer puts a unique OUI code into the first 3 bytes of the address.
c. Each manufacturer puts a unique OUI code into the first half of the address.
d. The part of the address that holds this manufacturer’s code is called the MAC.
e. The part of the address that holds this manufacturer’s code is called the OUI.
f. The part of the address that holds this manufacturer’s code has no specific name.
b. Each manufacturer puts a unique OUI code into the first 3 bytes of the address.
c. Each manufacturer puts a unique OUI code into the first half of the address.
e. The part of the address that holds this manufacturer’s code is called the OUI.
- Which of the following terms describe Ethernet addresses that can be used to send
one frame that is delivered to multiple devices on the LAN? (Choose two answers.)
c. Broadcast address
d. Multicast address
The term Ethernet refers to a family of ___ standards that together define the ______ and ______ layers of the world’s most popular wired LAN technology.
LAN
Physical
data link
Ethernet defines ____ LAN technology only
wired
All Ethernet standards come from the _____ and include the number _____ as the beginning part of the standard name.
IEEE
802.3
Ethernet acts like a single LAN technology because it uses the same ________ standard over all types of Ethernet physical links.
data link layer
The Ethernet standard defines a common Ethernet _____ and _______.
header
trailer.
While the __________ standards focus on sending bits over a cable, the Ethernet ________ protocols focus on sending an ___________ from source to destination Ethernet node.
physical layer
data-link
Ethernet frame
From a data-link perspective, nodes _________________.
build and forward frames
Define Ethernet link
Any physical cable between two ethernet nodes
As a rule, Ethernet NIC transmitters use the pair connected to pins ____; the NIC receivers use a pair of wires at pin positions ______.
1 and 2
3 and 6
Switch receivers use the wire pair at pins _____, and their transmitters use the wire pair at pins _____.
1 and 2
3 and 6
To allow a PC NIC to communicate with a switch, the UTP cable must also use a __________________.
straight- through cable pinout
A straight-through cable works correctly when the nodes use_______ pairs for transmitting data.
opposite
When two like devices connect to an Ethernet link, they both transmit on the same pins. In that case, you then need another type of cabling pinout called a ____________.
cross- over cable
Describe the pinout for a 100Base T
crossover cable.
Pin 1 to Pin 3
Pin 2 to Pin 6
Pin 3 to pin 1
Pin 6 to pin 2
Crossover cable: If the endpoints transmit on the _____ pin pair
same
Straight-through cable: If the endpoints transmit on ________ pin pairs
different
Which devices transmit on pins 1 and 2?
PC NIC’s
Routers
Wireless access points
Which devices transmit on pins 3 and 6?
Switches
Hubs
Name the fields in the ethernet frame
- Preamble
- SFD(start frame delimiter, tells the receiving device that the destination mac comes next).
- Dest MAC
- Source MAC
- Type(IPV4 or IPV6)
- Data and pad
- FCS
Mac Address
Ethernet addresses, also called Media Access Control (MAC) addresses, are 6-byte-long (48-bit- long) binary numbers. For convenience, most computers list MAC addresses as 12-digit hexa- decimal numbers.
OUI
The manufacturer agrees to give all NICs (and other Ethernet products) a MAC address that begins with its assigned 3-byte OUI. The manufacturer also assigns a unique value for the last 3 bytes, a number that manufacturer has never used with that OUI. As a result, the MAC address of every device in the universe is unique
In addition to unicast addresses, Ethernet also uses group addresses.
IEEE defines two general categories of group addresses for Ethernet:
Broadcast address: Frames sent to this address should be delivered to all devices on the Ethernet LAN. It has a value of FFFF.FFFF.FFFF.
Multicast addresses: Frames sent to a multicast Ethernet address will be copied and for- warded to a subset of the devices on the LAN that volunteers to receive frames sent to a specific multicast address.
Half duplex:
The device must wait to send if it is currently receiving a frame; in other words, it cannot send and receive at the same time
Full duplex:
The device does not have to wait before sending; it can send and receive at the same time.
When should a link use full or half duplex?
For all links between PCs and switches, or between switches, use full duplex. However, for any link connected to a LAN hub, the connected LAN switch and NIC port should use half-duplex.
Describe how nodes using half duplex recover from collisions by using CSMA/CD.
Step 1. A device with a frame to send listens until the Ethernet is not busy.
Step 2. When the Ethernet is not busy, the sender begins sending the frame.
Step 3.
The sender listens while sending to discover whether a collision occurs; colli- sions might be caused by many reasons, including unfortunate timing. If a colli- sion occurs, all currently sending nodes do the following:
A. They send a jamming signal that tells all nodes that a collision happened.
B. They independently choose a random time to wait before trying again, to
avoid unfortunate timing.
C. The next attempt starts again at Step 1.
Note that the hub itself does not use half-duplex logic, instead just repeating incoming signals out every other port.
Note that the hub itself does not use half-duplex logic, instead just repeating incoming signals out every other port.
