GLOSSARY Flashcards
66 Block
Traditionally used in corporate environments for cross-connecting phone system cabling. As
10Mbps LANs started to grow in popularity in the late 1980s and early 1990s, these termination
blocks were used to cross-connect Category 3 UTP cabling. The electrical characteristics
(specifically, crosstalk) of a 66 block, however, do not support higher-speed LAN technologies, such
as 100Mbps Ethernet networks.
110 Block
Because 66 blocks are subject to too much crosstalk for higher-speed LAN connections,
110 blocks can be used to terminate a cable (such as a Category 5 cable) being used for those higherspeed LANs.
802.11a
Ratified in 1999, this standard supports speeds as high as 54Mbps. Other supported data
rates (which can be used if conditions are not suitable for the 54Mbps rate) include 6, 9, 12, 18, 24,
36, and 48Mbps. The 802.11a standard uses the 5GHz band and the OFDM transmission method.
802.11ac
An IEEE wireless networking standard operating in the 5GHz range, with increased
throughput compared to previous Wi-Fi IEEE standards.
802.11b
Ratified in 1999, this standard supports speeds as high as 11Mbps. However, 5.5Mbps is
another supported data rate. The 802.11b standard uses the 2.4GHz band and the DSSS transmission
method.
802.11g
Ratified in 2003, this standard supports speeds as high as 54Mbps. Like 802.11a, other
supported data rates include 6, 9, 12, 18, 24, 36, and 48Mbps. However, like 802.11b, 802.11g
operates in the 2.4GHz band, which allows it to offer backward compatibility to 802.11b devices.
802.11g can use either the OFDM or DSSS transmission method.
802.11n
Ratified in 2009, this standard supports a variety of speeds, depending on its
implementation. Although the speed of an 802.11n network could approach 300Mbps (through the use
of channel bonding), many 802.11n devices on the market have speed ratings in the 130 Mbps–
150Mbps range. Interestingly, an 802.11n WLAN can operate in the 2.4GHz band, the 5GHz band, or
both simultaneously. 802.11n uses the OFDM transmission method.
Acceptable Use Policy (AUP)
Identifies what users of a network are and are not allowed to do on that
network. For example, retrieving sports scores during working hours via an organization’s Internet
connection might be deemed inappropriate by an AUP.
Access Control List
Rules typically applied to router interfaces, which specify permitted and
denied traffic.
Address Resolution Protocol
An A RP request is a broadcast asking for the MAC address
corresponding to a known IP address. An A RP reply contains the requested MAC address.
Administrative Distance (AD)
A routing protocol’s index of believable. Routing protocols with a
smaller AD are considered more believable than routing protocols with a higher AD.
Advanced Encryption Standard
Released in 2001, A ES is typically considered the preferred
symmetric encryption algorithm. A ES is available in 128-bit key, 192-bit key, and 256-bit key
versions.
alerts
Various monitoring devices and services can provide you with automated alerting as to
network events. This is often a key element in network security to quickly learn when a potential
ANT+
A wireless protocol for monitoring sensor data such as a person’s heart rate or a car’s tire
pressure, as well as for controlling systems such as indoor lighting and television sets. ANT+ is
designed and maintained by the ANT+ Alliance, which is owned by Garmin. It is based on the ANT
protocol.
anycast
An any cast communication flow is a one-to-nearest (from the perspective of a router’s
routing table) flow.
application layer (OSI model)
Layer 7 of the OSI model. This layer provides application services to
a network. An important yet often-misunderstood concept is that end-user applications do not reside
at the application layer. Instead, the application layer supports services used by end-user
applications. Another function of the application layer is advertising available services.
application layer (TCP/IP stack)
Addresses concepts described by Layers 5, 6, and 7 (that is, the
session, presentation, and application layers) of the OSI model.
arp command
Can be used in either the Microsoft Windows or the UNIX environment to see what a
Layer 2 MAC address corresponds to in a Layer 3 IP address.
asset management
As related to networks, this is a formalized system of tracking network
components and managing the lifecycle of those components.
asset tracking tags
Tags applied to physical network assets to permit the monitoring of the location
of these devices.
asymmetric encryption
With asymmetric encryption, the sender and receiver of a packet use
different keys.
Asynchronous Transfer Mode
A Layer 2 WAN technology that interconnects sites using
virtual circuits. These virtual circuits are identified by a pair of numbers, called the VPI/VCI pair. A
virtual path identifier (VPI) identifies a logical path, which can contain multiple virtual circuits. A
virtual circuit identifier (VCI) identifies the unique logical circuit within a virtual path.
Authentication Header (AH)
An IPSec protocol that provides authentication and integrity services.
However, it does not provide encryption services.
authentication server
In a network using 802.1X user authentication, an authentication server
(typically, a RADIUS server) checks a supplicant’s credentials. If the credentials are acceptable, the
authentication server notifies the authenticator that the supplicant is allowed to communicate on a
network. The authentication server also gives the authenticator a key that can be used to securely
transmit data during the authenticator’s session with the supplicant.
authenticator
In a network using 802.1X user authentication, an authenticator forwards a supplicant’s
authentication request on to an authentication server. After the authentication server authenticates the
supplicant, the authenticator receives a key that is used to communicate securely during a session with
the supplicant.
Automatic Private IP Addressing
Allows a networked device to self-assign an IP address
from the 169.254.0.0/16 network. Note that this address is only usable on the device’s local subnet
(meaning that the IP address is not routable).
availability
The measure of a network’s uptime.
badges
Identifiers worn by employees of an organization to assist with physical security.
bandwidth
The measure of network throughput capable on a network media or path
baseline
A collection of data portraying the characteristics of a network under normal operating
conditions. Data collected while troubleshooting can then be contrasted against baseline data.
Basic Rate Interface
A BRI circuit contains two 64Kbps B channels and one 16Kbps D
channel. Although such a circuit can carry two simultaneous voice conversations, the two B channels
can be logically bonded together into a single virtual circuit (by using PPP’s multilink interface
feature) to offer a 128Kbps data path.
basic service set
BSS - WLANs that have just one AP are called BSS WLANs. BSS WLANs are
said to run in infrastructure mode because wireless clients connect to an AP, which is typically
connected to a wired network infrastructure. A BSS network is often used in residential and SOHO
locations, where the signal strength provided by a single AP is sufficient to service all of the
WLAN’s wireless clients.
basic service set
BSS - WLANs that have just one AP are called BSS WLANs. BSS WLANs are
said to run in infrastructure mode because wireless clients connect to an AP, which is typically
connected to a wired network infrastructure. A BSS network is often used in residential and SOHO
locations, where the signal strength provided by a single AP is sufficient to service all of the
WLAN’s wireless clients.
biometrics
The use of unique characteristics of the body to provide access credentials and security.
For example, a thumbprint can be used to access a mobile device.
bit-error rate tester (BERT)
When troubleshooting a link where you suspect a high bit-error rate
(BER), you can use a piece of test equipment called a bit-error rate tester (BERT), which contains
both a pattern generator (which can generate a variety of bit patterns) and an error detector (which is
synchronized with the pattern generator and can determine the number of bit errors) and can calculate
a BER for the tested transmission link.
black-hole router
A router that drops packets that cannot be fragmented and are exceeding the MTU
size of an interface without notifying the sender.
block size
The number of IP addresses in a subnet, including the subnet’s address and the subnet’s
directed broadcast address.
Bluetooth
A wireless protocol for creating a personal area network, where a device such as a mobile
phone can send data to a headset, for example.
Bootstrap Protocol (BOOTP)
A legacy broadcast-based protocol used by networked devices to
obtain IP address information.
Border Gateway Protocol
Border Gateway Protocol (BGP) The only EGP in widespread use today. In fact, BGP is
considered to be the routing protocol that runs the Internet, which is an interconnection of multiple
autonomous systems. BGP is a path-vector routing protocol, meaning that it can use as its metric the
number of autonomous system hops that must be transited to reach a destination network, as opposed
to the number of required router hops.
basic service set
BSS - WLANs that have just one AP are called BSS WLANs. BSS WLANs are
said to run in infrastructure mode because wireless clients connect to an AP, which is typically
connected to a wired network infrastructure. A BSS network is often used in residential and SOHO
locations, where the signal strength provided by a single AP is sufficient to service all of the
WLAN’s wireless clients.
biometrics
The use of unique characteristics of the body to provide access credentials and security.
For example, a thumbprint can be used to access a mobile device.
bit-error rate tester (BERT)
When troubleshooting a link where you suspect a high bit-error rate
(BER), you can use a piece of test equipment called a bit-error rate tester (BERT), which contains
both a pattern generator (which can generate a variety of bit patterns) and an error detector (which is
synchronized with the pattern generator and can determine the number of bit errors) and can calculate
a BER for the tested transmission link.
black-hole router
A router that drops packets that cannot be fragmented and are exceeding the MTU
size of an interface without notifying the sender.
block size
The number of IP addresses in a subnet, including the subnet’s address and the subnet’s
directed broadcast address.
Bluetooth
A wireless protocol for creating a personal area network, where a device such as a mobile
phone can send data to a headset, for example.
Bootstrap Protocol (BOOTP)
A legacy broadcast-based protocol used by networked devices to
obtain IP address information.
Border Gateway Protocol
Border Gateway Protocol (BGP) The only EGP in widespread use today. In fact, BGP is
considered to be the routing protocol that runs the Internet, which is an interconnection of multiple
autonomous systems. BGP is a path-vector routing protocol, meaning that it can use as its metric the
number of autonomous system hops that must be transited to reach a destination network, as opposed
to the number of required router hops.
borrowed bits
Bits added to a classful subnet mask.
BPDU Guard
The ability of a switch to block a port where unexpected BPDUs are arriving from
another switch or attacker.
buffer overflow
This attack occurs when an attacker leverages a vulnerability in an application,
causing data to be written to a memory area (that is, a buffer) that’s being used by a different
application.
bus topology
Typically, this topology uses a cable running through the area requiring connectivity,
and devices to be networked can tap into that cable.
butt set
A piece of test equipment typically used by telephone technicians. The clips on a butt set canconnect to the tip and ring wires on a punch-down block (for example, a 66 block or a 110 block)
connecting to a telephone. This allows the technician to check the line (for example, to determine
whether a dial tone is present on the line and determine whether a call can be placed from the line).
basic service set
BSS - WLANs that have just one AP are called BSS WLANs. BSS WLANs are
said to run in infrastructure mode because wireless clients connect to an AP, which is typically
connected to a wired network infrastructure. A BSS network is often used in residential and SOHO
locations, where the signal strength provided by a single AP is sufficient to service all of the
WLAN’s wireless clients.
biometrics
The use of unique characteristics of the body to provide access credentials and security.
For example, a thumbprint can be used to access a mobile device.
bit-error rate tester (BERT)
When troubleshooting a link where you suspect a high bit-error rate
(BER), you can use a piece of test equipment called a bit-error rate tester (BERT), which contains
both a pattern generator (which can generate a variety of bit patterns) and an error detector (which is
synchronized with the pattern generator and can determine the number of bit errors) and can calculate
a BER for the tested transmission link.
black-hole router
A router that drops packets that cannot be fragmented and are exceeding the MTU
size of an interface without notifying the sender.
block size
The number of IP addresses in a subnet, including the subnet’s address and the subnet’s
directed broadcast address.
Bluetooth
A wireless protocol for creating a personal area network, where a device such as a mobile
phone can send data to a headset, for example.
Bootstrap Protocol (BOOTP)
A legacy broadcast-based protocol used by networked devices to
obtain IP address information.
Border Gateway Protocol
Border Gateway Protocol (BGP) The only EGP in widespread use today. In fact, BGP is
considered to be the routing protocol that runs the Internet, which is an interconnection of multiple
autonomous systems. BGP is a path-vector routing protocol, meaning that it can use as its metric the
number of autonomous system hops that must be transited to reach a destination network, as opposed
to the number of required router hops.
borrowed bits
Bits added to a classful subnet mask.
BPDU Guard
The ability of a switch to block a port where unexpected BPDUs are arriving from
another switch or attacker.
buffer overflow
This attack occurs when an attacker leverages a vulnerability in an application,
causing data to be written to a memory area (that is, a buffer) that’s being used by a different
application.
bus topology
Typically, this topology uses a cable running through the area requiring connectivity,
and devices to be networked can tap into that cable.
butt set
A piece of test equipment typically used by telephone technicians. The clips on a butt set canconnect to the tip and ring wires on a punch-down block (for example, a 66 block or a 110 block)
connecting to a telephone. This allows the technician to check the line (for example, to determine
whether a dial tone is present on the line and determine whether a call can be placed from the line).
cable certifier
If you are working with existing cable and want to determine its category, or if you
simply want to test the supported frequency range (and therefore data throughput) of the cable, you
can use a cable certifier.
cable modem
Attaches to the same coaxial cable (typically in a residence) that provides television
programming. A cable modem can use predetermined frequency ranges to transmit and receive data
over that coaxial cable.
cable tester
A cable tester can check the conductors in an Ethernet cable. It contains two parts. By
connecting these parts of the cable tester to each end of a cable under test, you can check the wires in
the cable for continuity (that is, check to make sure that there are no opens, or breaks, in a conductor).
In addition, you can verify an RJ-45 connector’s pin-outs (which are wires connected to the
appropriate pins on an RJ-45 connector).
campus area network
An interconnection of networks located in nearby buildings (for
example, buildings on a college campus).
captive portal
Typically a web page designed to collect the username and password of a user trying
to gain access to a network or application.
carrier-sense multiple access/collision avoidance (CSMA/CA)
Just as CSMA/CD is needed for
half-duplex Ethernet connections, CSMA/CA is needed for WLAN connections because of their halfduplex operation. Similar to how an Ethernet device listens to an Ethernet segment to determine
whether a frame exists on the segment, a WLAN device listens for a transmission on a wireless
channel to determine whether it is safe to transmit. In addition, the collision-avoidance part of the
CSMA/CA algorithm causes wireless devices to wait for a random back-off time before transmitting.
carrier-sense multiple access/collision detect (CSMA/CD)
Used on an Ethernet network to help
prevent a collision from occurring and to recover if a collision does occur. CSMA/CD is only needed
on half-duplex connections.
Central Office - CO
A building containing a telephone company’s telephone-switching equipment.
COs are categorized into five hierarchical classes. A Class 1 CO is a long-distance office serving a
regional area. A Class 2 CO is a second-level long-distance office; that is, it is subordinate to a Class
1 office. A Class 3 CO is a third-level long-distance office. A Class 4 CO is a fourth-level longdistance office, which provides telephone subscribers access to a live operator. A Class 5 CO is at
the bottom of the five-layer hierarchy and physically connects to customer devices in a local area.
Challenge Handshake Authentication Protocol (CHAP)
Like PAP, CHAP performs one-way
authentication. However, authentication is performed through a three-way handshake (challenge,
response, and acceptance messages) between a server and a client. The three-way handshake allows
a client to be authenticated without sending credential information across a network.
Central Office - CO
A building containing a telephone company’s telephone-switching equipment.
COs are categorized into five hierarchical classes. A Class 1 CO is a long-distance office serving a
regional area. A Class 2 CO is a second-level long-distance office; that is, it is subordinate to a Class
1 office. A Class 3 CO is a third-level long-distance office. A Class 4 CO is a fourth-level longdistance office, which provides telephone subscribers access to a live operator. A Class 5 CO is at
the bottom of the five-layer hierarchy and physically connects to customer devices in a local area.
Challenge Handshake Authentication Protocol (CHAP)
Like PAP, CHAP performs one-way
authentication. However, authentication is performed through a three-way handshake (challenge,
response, and acceptance messages) between a server and a client. The three-way handshake allows
a client to be authenticated without sending credential information across a network.
Challenge-Response Authentication Mechanism Message Digest 5 (CRAM-MD5)
A common
variant of HMAC frequently used in email systems. Like CHAP, CRAM-MD5 only performs one-way
authentication (the server authenticates the client).
Challenge-Response Authentication Mechanism Message Digest 5 (CRAM-MD5)
A common
variant of HMAC frequently used in email systems. Like CHAP, CRAM-MD5 only performs one-way
authentication (the server authenticates the client).
change management documentation
This important documentation explains the process whereby
changes are permitted in the network. This often consists of a series of approvals and testing steps.
channel bonding
With channel bonding, two wireless bands can be logically bonded together,
forming a band with twice the bandwidth of an individual band. Some literature calls channel bonding
40MHz mode, which refers to the bonding of two adjacent 20MHz bands into a 40MHz band.
channel service unit/data service unit (CSU/DSU)
Acts as a digital modem that terminates a digital
circuit (for example, a T1 or an E1 circuit).
circuit-switched connection
A connection that is brought up on an as-needed basis. A circuitswitched connection is analogous to a phone call, where you pick up a phone and dial a number, and a
connection is established based on the number you dial.
classful mask
A classful mask is the default subnet mask applied to Class A, B, and C IPv4 networks.
Specifically, Class A networks have a classful mask of 255.0.0.0. Class B networks have a classful
mask of 255.255.0.0, and Class C networks have a classful mask of 255.255.255.0.
classification
Classification is the process of placing traffic into different categories.
classless interdomain routing (CIDR)
Shortens a classful subnet mask by removing right-justified 1s
from a classful mask. As a result, CIDR allows contiguous classful networks to be aggregated. This
process is sometimes called route aggregation.
client
Defines the device an end user uses to access a network. This device might be a workstation,
laptop, smartphone with wireless capabilities, tablet, or variety of other end-user terminal devices.
client/server network
In a client/server network, a dedicated server (for example, a file server or a
print server) provides shared access to a resource (for example, files or a printer). Clients (for
example, PCs) on the network with appropriate privilege levels can gain access to those shared
resources.
client-to-site VPN
Also known as a remote-access VPN, a client-to-site VPN interconnects a remote
user with a site, as an alternative to dial-up or ISDN connectivity, at a reduced cost.
clustering
Connecting systems together with the intent of delivering network services from the cluster
to increase responsiveness and capacity. This solution also increases availability and redundancy.
coaxial cable
Also known as coax, a coaxial cable is composed of two conductors. One of the
conductors is an inner insulated conductor. This inner conductor is surrounded by another conductor.
This second conductor is sometimes made of a metallic foil or woven wire.
code-division multiple access(CDMA)
An example of multiple access, where several transmitters
can send information simultaneously over a single communication channel. This allows several users
to share a band of frequencies. CDMA is used as the access method in many mobile phone standards.
cold sites
These are redundant sites for a network, and they require time and effort to bring online.
collision
A collision occurs when two devices on an Ethernet network simultaneously transmit a
frame. Because an Ethernet segment cannot handle more than one frame at a time, both frames become
corrupted.
committed information rate (CIR)
The CIR of an interface is the average traffic rate over the period
of a second.
Common Address Redundancy Protocol (CARP)
An open standard variant of HSRP (Hot Standby
Router Protocol), which provides first-hop router redundancy.
congestion avoidance
If an interface’s output queue fills to capacity, newly arriving packets arediscarded (or tail dropped). Congestion avoidance can prevent this behavior. RED (Random Early
Detection) is an example of a congestion-avoidance mechanism.
congestion management
When a device, such as a switch or a router, receives traffic faster than it
can be transmitted, the device attempts to buffer (or store) the extra traffic until bandwidth becomes
available. This buffering process is called queuing or congestion management.
content engine
A dedicated appliance whose role is to locally cache content received from a remote
network (for example, a destination on the Internet). Subsequent requests for that content can be
serviced locally, from the content engine, thus reducing bandwidth demand on a WAN.
content switch
Can be used to load-balance requests for content across a group of servers containing
that content. If one of the servers in the group needs to have maintenance performed, that server could
be administratively removed from the group, as defined on the content switch. As a result, the content
switch can help maximize uptime when performing server maintenance. It minimizes the load on
individual servers by distributing its load across multiple identical servers. A content switch also
allows a network to scale because one or more additional servers could be added to the server group
defined on the content switch if the load on existing servers increases.
crimper
Used to attach a connector (for example, an RJ-45 connector) to the end of an unshielded
twisted-pair (UTP) cable.
current state modulation
One way to electrically or optically represent a binary 1 or 0 is to use
current state modulation, which represents a binary 1 with the presence of voltage (on a copper
cable) or the presence of light (on a fiber-optic cable). Similarly, the absence of light or voltage
represents a binary 0.
customer premise equipment (CPE)
This device resides at a customer site. A router, as an example,
can be a CPE that connects a customer with an MPLS service provider.
cyclic redundancy check (CRC)
A mathematical algorithm that is executed on a data string by both
the sender and the receiver of the data string. If the calculated CRC values match, the receiver can
conclude that the data string was not corrupted during transmission.
data link layer
As Layer 2 of the OSI model, this layer is concerned with the packaging of data into
frames and transmitting those frames on a network, performing error detection/correction, uniquely
identifying network devices with an address, and handling flow control.
decibel (dB)
A ratio of radiated power to a reference value. In the case of dBi, the reference value is
the signal strength (that is, the power) radiated from an isotropic antenna, which represents a
theoretical antenna that radiates an equal amount of power in all directions (in a spherical pattern).
An isotropic antenna is considered to have gain of 0 dBi.
decibel (dB) loss
A loss of signal power. If a transmission’s dB loss is too great, the transmission
cannot be properly interpreted by the intended recipient.
dedicated leased line
A logical connection interconnecting two sites. This logical connection might
physically connect through a service provider’s facility or a telephone company’s central office. The
expense of a dedicated leased line is typically higher than other WAN technologies offering similar
data rates, because with a dedicated leased line, a customer does not have to share bandwidth with
other customers.
default gateway
The IP address of a router (or multilayer switch) to which a networked device
sends traffic destined for a subnet other than the device’s local subnet.
default static route
A default static route is an administratively configured entry in a router’s routing
table that specifies where traffic for all unknown networks should be sent.
demarc
Also known as a demarcation point or a demarc extension, this is the point in a telephone
network where the maintenance responsibility passes from a telephone company to a subscriber
(unless the subscriber purchased an inside wiring plan). This demarc is typically a box mounted to
the outside of a customer’s building (for example, a residence).
demilitarized zone (DMZ)
Often contains servers that should be accessible from the Internet. This
approach would, for example, allow users on the Internet to initiate an email or a web session coming
into an organization’s email or web server. However, other protocols would be blocked.
denial of service (DoS)
A DoS attack floods a system with an excessive amount of traffic or
requests, which consumes the system’s processing resources and prevents the system from responding
to many legitimate requests.
designated port
In an STP topology, every network segment has a single designated port, which is the
port on that segment that is closest to the root bridge, in terms of cost. Therefore, all ports on a root
bridge are designated ports.
differential backup
A type of partial backup of a data set. All data that has changed since the last full
backup is targeted by the backup job.
differentiated services (DiffServ)
As its name suggests, DiffServ differentiates between multiple
traffic flows. Specifically, packets are marked, and routers and switches can then make decisions (for
example, dropping or forwarding decisions) based on those markings.
dig command
Can resolve an FQDN to an IP address on UNIX hosts.
digital subscriber line
A group of technologies that provide high-speed data transmission over
existing telephone wiring. DSL has several variants, which vary in data rates and distance limitations.
Three of the more popular DSL variants include asymmetric DSL (ADSL), symmetric DSL (DSL),
and very high bit-rate DSL (VDSL).
direct-sequence spread spectrum (DSSS)
Modulates data over an entire range of frequencies using
a series of symbols called chips. A chip is shorter in duration than a bit, meaning that chips are
transmitted at a higher rate than the actual data. These chips not only represent encoded data to be
transmitted, but also what appears to be random data. Because both parties involved in a DSSS
communication know which chips represent actual data and which chips do not, if a third-party
intercepted a DSSS transmission, it would be difficult for that party to eavesdrop on the data because
he would not easily know which chips represented valid bits. DSSS is more subject to environmental
factors, as opposed to FHSS and OFDM, because it uses an entire frequency spectrum.
distance vector
A category of routing protocol that sends a full copy of its routing table to its directly
attached neighbors.
dotted-decimal notation
A method of writing an IPv4 address or subnet mask, where groups of 8 bits
(called octets) are separated by periods.
dual stack
The ability of a network interface to run multiple protocols, such as IP and IPv6
Dynamic Host Configuration Protocol (DHCP)
Dynamically assigns IP address information (for
example, IP address, subnet mask, DNS server’s IP address, and default gateway’s IP address) to
network devices.
Dynamic Host Configuration Protocol (DHCP) snooping
The process of securing the network
against a rogue DHCP server attack or other types of DHCP security attacks.