CCENT vocab - sec 1

The general topic of how on one computer, two adjacent layers in a networking architectural model work together, with the lower layer providing services to the higher layer

On a computer that receives data over a network, the process in which the device interprets the lower-layer headers and, when finished with each header, removes the header, revealing the next-higher-layer PDU.

The placement of data from a higher-layer protocol behind the header (and in some cases, between a header and trailer) of the next-lower-layer protocol. For example, an IP packet could be encapsulated in an Ethernet header and trailer before being sent over an Ethernet.

A term referring to a data-link header and trailer, plus the data encapsulated between the header and trailer.

A generic term referring to any set of protocols and standards collected into a comprehensive grouping that, when followed by the devices in a network, allows all the devices to communicate. Examples include TCP/IP and OSI

A logical grouping of information that includes the network layer header and encapsulated data, but specifically does not include any headers and trailers below the networking layer.

A generic term referring to the header defined by some layer of a networking model, and the data encapsulated by the header (and possibly a trailer) of that layer, but specifically not including any lower-layer headers and trailers

The communication between two networking devices for the purposes of the functions defined at a particular layer of networking model, with that communication happening by using a header defined by that layer of the model. The two devices set value in the header, send the header and encapsulated data, with the receiving device(s) interpreting the header to decide what action to take.

In TCP, a term used to describe a TCP header and its encapsulated data (also called an L4PDU). Also in TCP, the process of accepting a large church of data from the application layer and breaking it into smaller pieces that fit into TCP segments. In Ethernet, a segment is either a single Ethernet cable or a single collision domain (no matter how many cables are used).

• 4-pair copper cabling
• speed of 1000 Mbps (1 Gbps)
• 100 meter max length

• 2-pair copper cabling
• speed of 100 Mbps
• 100 meter max length

• 2-pair twisted cable (cat 3, 4, or 5)
• speed of 10 Mbps
• 100 meter max length

An Ethernet cable that swaps the pair used for transmission on one device to a pair used for receiving on the device on the opposite end of the cable. In 10BASE-T & 10BASE-TX networks, this cable swaps the pair at pins 1,2 to pins 3,6 on the other end of the cable, and the pair at pins 3,6 to pins 1,2 as well.

• Carrier Sense Multiple Access with Collision Detection
• A media access mechanism in which devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time.

Generically, any communication in which two communicating devices can concurrently send and receive data. In Ethernet LANs, the allowance for both devices to send and receive at the same time, allowed when both devices disable their CSMA/CD logic.

Generically, any communication in which only one device at a time can send data. In Ethernet LANs, the normal result of the CSMA/CD algorithm that enforces the rule that only one device should send at any point in time.

A LAN device that provides a centralized connection point for LAN cabling, repeating any received electrical signal out all other ports, thereby creating a logical bus. Hubs do not interpret the electrical signals as a frame of bits, so hubs are considered to be Layer 1 devices.

The documentation and implementation of which wires inside a cable connect to each pin position in any connector

A field in the LAN header that identifies the type of header that follows the LAN header. Includes the DIX Ethernet Type field, the IEEE 802.2 DSAP field, and the SNAP protocol Type field

An Ethernet that uses a hub, or even the original coaxial cabling, which results in the devices having to take turns sending data, sharing the available bandwidth.

In Ethernet, a cable that connects the wire on pin 1 on one end of the cable to pin 1 on the other end of the cable, pin 2 on one end to pin 2 on the other end, and so on.

A network device that filters, forwards, and floods Ethernet frames based on the destination address of each frame

An Ethernet that uses a switch, and particularly not a hub, so that devices connected to one switch port do not have to contend to use the bandwidth available on another port. This term contrasts with "shared Ethernet", in which the devices must share bandwidth, whereas switched Ethernet provides much more capacity, as the devices do not have to share the available bandwidth.

Transmission medium consisting of two insulated wires, with the wires twisted around each other in a spiral. An electrical circuit flows over the wire pair, with the current in opposite directions on each wire, which significantly reduces the interference between the two wires.

In Frame Relay, the physical serial link that connects a Frame Relay DTE device, usually a router, to a Frame Relay switch. The access link uses the same physical layer standards as do point-to-point leased lines

A serial link between two routers, created without CSU/DSUs, by connecting a DTE cable to one router and a DCE cable to the other. Typically used in labs to build serial links without the expense of an actual leased line from the telco.

The process of supplying a signal over cable, either on a separate pin on a serial cable or as part of the signal transitions in the transmitted signal, so that the receiving device can keep synchronization with the sending device.

Data Terminal Equipment. From a layer 1 perspective, the DTE synchronizes its clock based on the clock sent by the DCE. From a packet-switching perspective, the DTE is the device outside the service provider's network, typically a router.

Channel Service Unit / Digital Service Unit. A device that understands the Layer 1 details of serial links installed by a telco and how to use a serial cable to communicate with networking equipment such as routers

Data communications equipment. From a physical layer perspective, the device providing the clocking on a WAN link, typically a CSU/DSU, is the DCE. From a packet-switching perspective, the service provider's switch, to which a router might connect, is considered the DCE.

Digital Signal Level 0. A 64-kbps line or channel of a faster line inside a telco whose origins are to support a single voice call using the original voice (PCM) codecs

Digital Signal Level 1. A 1.544-Mbps line from the telco, with 24 DS0 channels of 64-kbps each, plus an 8-kbps management and framing channel. Also called a T1

An international standard data-link protocol that defines the capabilities to create a frame-switched (packet-switched) service, allowing DTE devices (typically routers) to send data to many other devices using a single physical connection to the Frame Relay service.

High-Level Data Link Control. A bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO)

A serial communications circuit between two points, provided by some service provider, typically a telco. Because the telco does not sell a physical cable between the two endpoints, instead charging a monthly fee for the ability to send bits between the two sites, this service is considered to be a leased service.

A generic reference to network services, typically WAN services, in which the service examines the contents of the transmitted data to make some type of forwarding decision. This term is mainly used to contrast with the WAN term "circuit switching," in which the provider sets up a (Layer 1) circuit between two devices, and the provider makes no attempt to interpret the meaning of the bits.

Point-to-Point Protocol. A protocol that provides router-to-router and host-to-network connections over synchronous point-to-point and asynchronous point-to-point circuits.

A type of cable with many different styles of connectors used to connect a router to an external CSU/DSU on a leased-line installation

The imposition of time ordering on a bit stream. Practically, a device will try to use the same speed as another device on the other end of a serial link. However, by examining transitions between voltage states on the link, the device can notice slight variations in the speed on each end and can adjust its speed accordingly.

A line from the telco that allows transmission of data at 1.544-Mbps, with the ability to treat the line as 24 different 64-kbps DS0 channels (plus 8-kbps of overhead)

In packet-switched services like Frame Relay, VC refers to the ability of two DTE devices (typically routers) to send and receive data directly to each other, which supplies the same function as a physical leased line (leased circuit), but doing so without a physical circuit. This term is meant as a contrast with a leased line or a leased circuit.

Address resolution protocol. An Internet protocol used to map an IP address to a MAC address. Defined in RFC 826

On an IP host, the IP address of some router to which the host sends packets when the packet's destination address is on a subnet other than the local subnet

Dynamic Host Configuration Protocol. A protocol used by hosts to dynamically discover and lease an IP address, and learn the correct subnet mask, default gateway, and DNS server IP address

Domain Name System. An application layer protocol used throughout the Internet for translating hostnames into their associated IP addresses

A term used to describe a part of an IPv4 address that is used to uniquely identify a host inside a subnet. The host part is identified by the bits of value 0 in the subnet mask

In IPv4, a 32-bit address assigned to hosts using TCP/IP. Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing, and the host number is used to address an individual host within the network or subnetwork.

A generic reference to addresses as defined by Layer 3 protocols, which do not have to be concerned with the physical details of the underlying physical media. Used mainly to contrast these addresses with data-link addresses, which are generically considered to be physical addresses because they differ based on the type of physical medium

In IPv4, a special address in each classful network that can be used to broadcast a packet to all hosts in that same classful network. Numerically, the address has the same value as the network number in the network part of the address, and all 255s in the host octets–for example, 10.255.255.255 is the network broadcast adders for the classful network 10.0.0.0

A number that uses dotted decimal notation like IP addresses, but the number itself represents all hosts in a single Class A, B, or C IP network

The portion of an IPv4 address that is either 1, 2, or 3 octets/bytes long, based on whether the address is in a Class A, B, or C network

A list of routes in a router, with each route listing the destination subnet and mask, the router interface out which to forward packets destined to that subnet, and, as needed, the next-hop router's IP address

A special address in each subnet, specifically the largest numeric address in the subnet, designed so that packets sent to this address should be delivered to all hosts in that subnet

In IPv4, a dotted decimal number that represents all addresses in a single subnet. Numerically, the smallest value in the range of numbers in a subnet, reserved so that it cannot be used as a unicast IP address by a host

In a sub netted IPv4 address, interpreted with glassful addressing rules, one of three parts of the structure of an IP address, with the subnet part uniquely identifying different subnets of a classful IP network.

The term used by Cisco to refer to a variety of security tools that help prevent various attacks, including antivirus, anti-phishing, and anti-spam

The process by which a connection-oriented protocol creates a connection. With TCP, a connection is established by a three-way transmission of TCP segments

Denial of Service. A type of attack whose goal is to cause problems by preventing legitimate users from being able to access services, thereby preventing the normal operation of computers and networks.

The process of discovering whether or not a data-link level frame was changed during transmission. This process typically uses a Frame Check Sequence (FCS) field in the data-link layer

The process of noticing when some transmitted data was not successfully received and resending the data until it is successfully received.

A device that forwards packets between the less secure and more secure parts of the network, applying rules that determine which packets are allowed to pass, and which are not.

The process of regulating the amount of data sent by a sending computer toward a receiving computer. Several flow control mechanisms exist, including TCP flow control, which uses windowing.

A process used by protocols that do error recovery in which the number that acknowledges data lists the next data that should be sent, not the last data that was successfully received

Hypertext Transfer Protocol. The protocol used by web browsers and web servers to transfer files, such as text and graphic files.

A security function that examines more complex traffic patterns against a list of both known attack signatures and general characteristics of how attacks may be carried out, rating each perceived threat and reporting the threats

A security function that examines more complex traffic patterns against a list of both known attack signatures and general characteristics of how attacks may be carried out, rating each perceived threat and reacting to prevent the more significant attacks

A networking function, included in TCP, in which the protocol defines how the sending host should number the data transmitted, defines how the receiving device should attempt to reorder the data if it arrives out of order, and specifies to discard the data if it cannot be delivered in order.

In TCP and UDP, a number that is used to uniquely identify the application process that either sent (source port) or should receive (destination port) data. In LAN switching, another term for switch interface.

A generic reference to how the error recovery feature works in many protocols, including TCP, in which the receiver must send an acknowledgment that either implies that the data was (positively) received, or send an acknowledgment that implies that some data was lost, so the sender can resend the lost data.

In TCP, a term used to describe a TCP header and its encapsulated data (also called a L4PDU). Also in TCP, the process of accepting a large chunk of data from the application layer and breaking it into smaller pieces that fit into TCP segments. In Ethernet, a segment is either a single Ethernet cable or a single collision domain (no matter how many cables are used).

For protocols such as TCP that allow the receiving device to dictate the amount of data the sender can send before receiving an acknowledgment–a concept called a window–a reference to the fact that the mechanism to grant future windows is typically just a number that grows upward slowly after each acknowledgment, sliding upward.

Universal Resource Locator. A standard for how to refer to any piece of information retrievable via a TCP/IP network, most notably used to identify web pages.

The process of securing communication between two devices whose packets pass over some public and unsecured network, typically the Internet. VPNs encrypt packets so that the communication is private and authenticate the identity of the endpoints

Voice over IP. The transport of voice traffic inside IP packets over an IP network

Software, running on some computer, that stores web pages and send those web pages to web clients (web browsers) that request the web pages