CCNA Terms

hop

The journey from one node to the next in the path is called a hop, and the job of the Data Link Layer is to provide hop-to-hop delivery of messages.

utp

unshielded twisted pair

sfp

small form-factor pluggable

smf

single-mode fiber

mmf

multi-mode fiber

emi

electromagnetic interference, which refers to the disruption of electrical signals caused by external electromagnetic fields.

forward

(a method of directing data packets through a network to their destination.) To forward a message is to send it to the next node in the path to the destination, whether that is the final destination node itself or the next router in the path to the destination.

data encapsulation

The process of adding headers (and trailers) to data before sending it over a network is called encapsulation. To summarize that process:

The Application Layer protocol prepares data.

Layer 4 encapsulates the data with a header addressed to a port number on the destination host.

Layer 3 encapsulates the data with a header addressed to the IP address of the destination host.

Layer 2 encapsulates the data with a header addressed to the MAC address of the next hop. It also encapsulates the data with a trailer, used to check for errors.

The host transmits the bits of data over the physical medium (e.g., encoded as electrical signals over a UTP cable).

Data de-encapsulation

The process of removing headers and trailers from received data as it moves up the OSI model layers to the application layer. This allows the application to interpret the original data sent over the network. Opposite if encapsulation

segment

The combination of data and a Layer 4 header is called a segment.

packet

The combination of a segment and a Layer 3 header is called a packet.

frame

the combination of a packet and a Layer 2 header/trailer is called a frame

protocol data unit

A general term that describes a format used in networking for data transmission, encompassing segments, packets, frames, and other specific units.

shell

A user interface for access to an operating system's services, often used for command line inputs.

rollover cable

The wiring of a rollover cable, used to connect a PC to the RJ45 console port of a network device (as shown).

PDU

The Protocol Data Unit (PDU) is a specific format used in networking that defines the packaging of data for transmission across the network.

Receiver Clock

A clock signal used by a receiver in data communication to synchronize with the sender's data transmission timing.

type

of Protocol Data Unit that indicates the nature of the data being transferred, such as a segment, frame, or packet.

EtherType field

is a two-byte field in an Ethernet frame that indicates the protocol encapsulated in the payload of the frame, helping the receiving device understand how to process the data. (When used to indicate the type of the encapsulated packet, this field is called the EtherType field.)

FCS

A Frame Check Sequence used in data link layer protocols for error detection in transmitted frames. The Frame Check Sequence (FCS) is the only field of the Ethernet trailer. It is 4 bytes in length and is used to detect corrupted data in the frame.

checksum

Before a device sends a frame, it uses an algorithm to calculate a checksum, a small block of data that is appended to the end of the frame as the FCS field. It is a value derived from the data in the frame, allowing the receiving device to verify the integrity of the transmitted data by re-calculating the checksum and comparing it to the received value.

CRC

A Cyclic Redundancy Check (CRC) is a method used for error-checking in network communications. It calculates a short, fixed-length binary sequence from the data being sent, which helps detect any changes or corruptions in the data during transmission. The term cyclic refers to the kind of algorithm used to calculate the checksum. Redundancy means that the field is redundant—it expands the size of the message but doesn’t add any additional information. Check is self-explanatory—it is used to check if the frame traveled from source to destination without the data being corrupted.

slot

A slot is a group of ports on a network device. It designates a specific location for connecting devices or interfaces, allowing them to communicate with the network.

Known unicast frame (forward)

The switch will send the frame out of the port specified by the MAC address’s entry in the MAC address table.This type of frame is sent to a specific device identified by its unique MAC address, ensuring efficient data transmission.

Unknown unicast frame (flood)

The switch will send the frame out of all ports except the one it was received on.

Address Resolution Protocol (ARP)

ARP allows a host to learn the MAC address of another host in the LAN. ARP involves two messages: an ARP request (used to ask another host what its MAC address is) and an ARP reply (used to inform another host of this host’s MAC address). The ARP request message is sent in a new kind of frame: not unicast but broadcast. The ARP reply is a unicast frame sent to the MAC address of the host that sent the ARP request.

Internet Control Message Protocol (ICMP)

ICMP is a network layer protocol used for error messaging and operational queries in Internet Protocol (IP) networks. It helps manage network communications by sending error messages and diagnostic information like ping results.

dotted decimal notation

split the 32-bit IPv4 address into four groups of 8 bits called octets, separated by a period, and then convert each of the octets to decimal; this is called dotted decimal notation