Comptia Network+
5.0 Network Troubleshooting
Duplexing issues ANS: Originally, all Ethernet connections were half-duplex, meaning that only one of
the connected systems could transmit at a time. This was because the protocol used a single wire pair
for both transmitting and receiving data. Beginning with Fast Ethernet (100Base-T), the protocol
included a full duplex mode, which uses separate wire pairs for the TX (transmit) and RX (receive)
connections. This enables the connected systems to transmit and receive data simultaneously,
increasing the theoretical transmission speed of the link to 200 Mbps.
Virtually all Ethernet networks today run in full duplex mode. When establishing a connection, the
network interface adapters negotiate the best possible speed and duplex mode. Typically, duplexing
issues result when one or both of the connected devices has a manually configured duplex setting. If one
device is set to half duplex and the other to full duplex, the result will be a large number of collisions and
errors, degrading the network performance dramatically.
Administrators typically allow workstations to autonegotiate their duplex and speed settings. However,
it is more common for them to manually configure the interfaces on switches and routers, in which case
a duplex mismatch could occur by accident. When troubleshooting a slow Ethernet network with
excessive collisions, duplexing settings are one of the configuration settings to check early in the
process.
1.0 Networking Fundamentals 24%
Layer 1 - Physical ANS: This layer provides the actual physical connection between the computer and
the network. Computers communicate at this layer by generating signals and transmitting them over a
network medium.
For outgoing communications, this layer receives data from a protocol running on the layer above it (the
data link layer), converts the data into a binary code appropriate for the medium, and transmits it over
the network.
For incoming communications, it receives the signals from the network and converts them into an
appropriate form for the data link protocol.
,1.0 Networking Fundamentals 24%
Layer 2 - Data link ANS: This layer of the OSI model is closely associated with the physical layer. The two
together implement the computer's connection to and communication with the LAN to which the device
is attached.
Includes Error Detection and Protocol Identification. This layer also uses a Media Access Control
mechanism to prevent two devices from transmitting simultaneously and causing a data collision.
1.0 Networking Fundamentals 24%
Layer 3 - Network ANS: Physical and Data Link are concerned only with local network communications.
However, it is the responsibility of this layer to deliver data to its final destination.
Devices at this layer include routers. Routers connect individual networks together, forming an
internetwork.
Functions at this layer include End-to-End addressing, Routing, Fragmentation, and Protocol
Identification.
1.0 Networking Fundamentals 24%
Layer 4 - Transport ANS: The protocols at this layer of the OSI model provide additional end-to-end
communication services, such as guaranteed delivery and flow control, to the adjacent layers, as
needed.
Functions at this layer include Data Segmentation and Packet Acknowledgment.
1.0 Networking Fundamentals 24%
Layer 5 - Session ANS: The functions associated with this layer are mostly concerned with the
establishment, maintenance, and termination of communications during a connection between two end
systems, called a session.
,Important functions at this layer include Dialog control and Dialog separation.
1.0 Networking Fundamentals 24%
Layer 6 - Presentation ANS: This layer presents data to the Application layer and is responsible for data
translation and code formatting.
A successful data- transfer technique is to adapt the data into a standard format before transmission.
Computers are configured to receive this generically formatted data and then convert it back into its
native format for reading— for example, from EBCDIC to ASCII.
By providing translation services, the this layer ensures that the data transferred from one system's
Application layer can be read and understood by the Application layer on another system.
1.0 Networking Fundamentals 24%
Layer 7 - Application ANS: This layer is the entrance point to the protocol stack for applications running
on the computer.
1.0 Networking Fundamentals 24%
Data encapsulation ANS: As outgoing data travels down through the protocol stack to the network
medium, it undergoes a process called data encapsulation, which is the functional equivalent of putting
a letter into an envelope for mailing.
1.0 Networking Fundamentals 24%
Data decapsulation ANS: For packets arriving at the destination system, the process occurs in reverse,
with the data passed up through the OSI model layers, a processed called decapsulation. Each layer
processes the incoming packet by reading and stripping off the header and then passing the payload up
to the correct protocol at the next higher layer.
, 1.0 Networking Fundamentals 24%
Ethernet header ANS: As traffic arrives at a switch, the device reads the Ethernet header of each packet,
specifically the MAC address fields. The switch then compiles a table containing those MAC addresses,
associating each packet's Source Address with the number of the switch port over which the packet
arrived.
1.0 Networking Fundamentals 24%
Internet Protocol (IP) header ANS: On the network layer, IP is the protocol responsible for end-to-end
transmissions between the packet's sender and its ultimate recipient.
The IP header contains IP addresses that identify the two end systems.
1.0 Networking Fundamentals 24%
Transmission Control Protocol (TCP)/
User Datagram Protocol (UDP) headers ANS: The transport layer functions are implemented in headers
applied by each protocol.
The TCP header includes TCP flags (the "SYN", "ACK" and "FIN") that the protocol uses to establish a
connection between the sending and receiving systems and then break down the connection after the
data transmission.
UDP is connectionless and therefore needs only a comparatively small 8-byte header.
1.0 Networking Fundamentals 24%
TCP flags ANS: the "SYN", "ACK" and "FIN"
URG: Urgent pointer field significant
ACK: Acknowledgment field significant
5.0 Network Troubleshooting
Duplexing issues ANS: Originally, all Ethernet connections were half-duplex, meaning that only one of
the connected systems could transmit at a time. This was because the protocol used a single wire pair
for both transmitting and receiving data. Beginning with Fast Ethernet (100Base-T), the protocol
included a full duplex mode, which uses separate wire pairs for the TX (transmit) and RX (receive)
connections. This enables the connected systems to transmit and receive data simultaneously,
increasing the theoretical transmission speed of the link to 200 Mbps.
Virtually all Ethernet networks today run in full duplex mode. When establishing a connection, the
network interface adapters negotiate the best possible speed and duplex mode. Typically, duplexing
issues result when one or both of the connected devices has a manually configured duplex setting. If one
device is set to half duplex and the other to full duplex, the result will be a large number of collisions and
errors, degrading the network performance dramatically.
Administrators typically allow workstations to autonegotiate their duplex and speed settings. However,
it is more common for them to manually configure the interfaces on switches and routers, in which case
a duplex mismatch could occur by accident. When troubleshooting a slow Ethernet network with
excessive collisions, duplexing settings are one of the configuration settings to check early in the
process.
1.0 Networking Fundamentals 24%
Layer 1 - Physical ANS: This layer provides the actual physical connection between the computer and
the network. Computers communicate at this layer by generating signals and transmitting them over a
network medium.
For outgoing communications, this layer receives data from a protocol running on the layer above it (the
data link layer), converts the data into a binary code appropriate for the medium, and transmits it over
the network.
For incoming communications, it receives the signals from the network and converts them into an
appropriate form for the data link protocol.
,1.0 Networking Fundamentals 24%
Layer 2 - Data link ANS: This layer of the OSI model is closely associated with the physical layer. The two
together implement the computer's connection to and communication with the LAN to which the device
is attached.
Includes Error Detection and Protocol Identification. This layer also uses a Media Access Control
mechanism to prevent two devices from transmitting simultaneously and causing a data collision.
1.0 Networking Fundamentals 24%
Layer 3 - Network ANS: Physical and Data Link are concerned only with local network communications.
However, it is the responsibility of this layer to deliver data to its final destination.
Devices at this layer include routers. Routers connect individual networks together, forming an
internetwork.
Functions at this layer include End-to-End addressing, Routing, Fragmentation, and Protocol
Identification.
1.0 Networking Fundamentals 24%
Layer 4 - Transport ANS: The protocols at this layer of the OSI model provide additional end-to-end
communication services, such as guaranteed delivery and flow control, to the adjacent layers, as
needed.
Functions at this layer include Data Segmentation and Packet Acknowledgment.
1.0 Networking Fundamentals 24%
Layer 5 - Session ANS: The functions associated with this layer are mostly concerned with the
establishment, maintenance, and termination of communications during a connection between two end
systems, called a session.
,Important functions at this layer include Dialog control and Dialog separation.
1.0 Networking Fundamentals 24%
Layer 6 - Presentation ANS: This layer presents data to the Application layer and is responsible for data
translation and code formatting.
A successful data- transfer technique is to adapt the data into a standard format before transmission.
Computers are configured to receive this generically formatted data and then convert it back into its
native format for reading— for example, from EBCDIC to ASCII.
By providing translation services, the this layer ensures that the data transferred from one system's
Application layer can be read and understood by the Application layer on another system.
1.0 Networking Fundamentals 24%
Layer 7 - Application ANS: This layer is the entrance point to the protocol stack for applications running
on the computer.
1.0 Networking Fundamentals 24%
Data encapsulation ANS: As outgoing data travels down through the protocol stack to the network
medium, it undergoes a process called data encapsulation, which is the functional equivalent of putting
a letter into an envelope for mailing.
1.0 Networking Fundamentals 24%
Data decapsulation ANS: For packets arriving at the destination system, the process occurs in reverse,
with the data passed up through the OSI model layers, a processed called decapsulation. Each layer
processes the incoming packet by reading and stripping off the header and then passing the payload up
to the correct protocol at the next higher layer.
, 1.0 Networking Fundamentals 24%
Ethernet header ANS: As traffic arrives at a switch, the device reads the Ethernet header of each packet,
specifically the MAC address fields. The switch then compiles a table containing those MAC addresses,
associating each packet's Source Address with the number of the switch port over which the packet
arrived.
1.0 Networking Fundamentals 24%
Internet Protocol (IP) header ANS: On the network layer, IP is the protocol responsible for end-to-end
transmissions between the packet's sender and its ultimate recipient.
The IP header contains IP addresses that identify the two end systems.
1.0 Networking Fundamentals 24%
Transmission Control Protocol (TCP)/
User Datagram Protocol (UDP) headers ANS: The transport layer functions are implemented in headers
applied by each protocol.
The TCP header includes TCP flags (the "SYN", "ACK" and "FIN") that the protocol uses to establish a
connection between the sending and receiving systems and then break down the connection after the
data transmission.
UDP is connectionless and therefore needs only a comparatively small 8-byte header.
1.0 Networking Fundamentals 24%
TCP flags ANS: the "SYN", "ACK" and "FIN"
URG: Urgent pointer field significant
ACK: Acknowledgment field significant
