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A B C D E F G H I J K L M N O P Q R S T
U V W X Y Z
ARP
Address Resolution Protocol. is an internet protocol used to map an IP
address to a MAC address. ARP is a required TCP/IP standard defined in
RFC 826. ARP resolves IP addresses used by TCP/IP-based software to Media
Access Control addresses used by LAN hardware. ARP provides the following
protocol services to hosts located on the same physical network.
Media access control addresses are obtained by using a network broadcast request in the form of the question "What is the media access control address for a device that is configured with the enclosed IP address?"
When an ARP request is answered, both the sender of the ARP reply and the original ARP requester record each other's IP address and media access control address as an entry in a local table called the ARP cache for future reference.
Access List
A list kept by routers to control access to or from the router for a number of services (for example, to prevent packets with a certain IP address from leaving a particular interface on the router).
Bandwidth
The speed at which a communications system can transfer data, usually measured
in bits per second.
Broadcast
Address
A special address reserved for sending a message to all stations. Generally,
a broadcast address is a MAC destination address of all ones
BPS
Short for Bits Per Second. In data communications, bits per second (abbreviated bps) is a common measure of data speed for computer modem and transmission carriers. As the term implies, the speed in bps is equal to the number of bits transmitted or received each second.
Bottleneck
Bottlenecks refers to the delay in transmission of data through the circuits
of a computer's microprocessor or over a TCP/IP network. The delay typically
occurs when a system's bandwidth cannot support the amount of information
being relayed at the speed it is being processed. There are, however,
many factors that can create a bottleneck in a system.
Bottlenecks affect network performance by slowing down the flow of information transmitted across networks. TCP/IP connections were originally designed to transmit only text files, and the proliferation of bandwidth-intensive transmissions such as high-resolution graphics has caused bottlenecks in the process; therefore, the data moves more slowly across networks.
Broadcast Storm
An undesirable network event in which many broadcasts are sent simultaneously across all network segments. A broadcast storm uses substantial network bandwidth and, typically, causes network time-outs. Broadcast storms can usually be prevented by carefully configuring a network to block illegal broadcast messages.
Buffer
A storage area used for handling data in transit. Buffers are used in internetworking
to compensate for differences in processing speed between network devices.
Bursts of data can be stored in buffers until they can be handled by slower
processing devices. Sometimes referred to as a packet buffer.
Byte
A byte is a unit of data that is eight binary digits long. A byte is the unit most computers use to represent a character such as a letter, number, or typographic symbol (for example, "g", "5", or "?")
CDP
Short for Cisco Discovery Protocol. CDP is a media-
and protocol-independent device-discovery protocol that runs on all Cisco-manufactured
equipment including routers, access servers, bridges, and switches. Using
CDP, a device can advertise its existence to other devices and receive
information about other devices on the same LAN or on the remote side
of a WAN. The devices do not need to have any network layer protocols
configured in order to use CDP, although if these addresses are configured
CDP will discover them.. Each device configured for CDP sends out periodic
messages to a MAC layer multicast address. these advertisements include
information about the capabilities and software version of the advertising
platform. This gives you an easy way to see other Cisco devices on your
network without having to figure out which devices are Cisco by the vendor
code embedded in the Media Access Control address.
Configuration Register
All Cisco Router have a 16-bit configuration register, which is stored in a special memory location in NVRAM. This register controls a number of function, some of which are listed below:
Force the system into the bootstrap program
Select a bootsource and default boot file name
Enable or disable the console Break function
Set the console terminal baud rate
Load operating software from ROM
Enabling booting from a TFTP Server
The configuration register
boot field is the portion of the configuration register that determines
whether the router loads an IOS image, and if so where to get this image
from. The least significant four bits, bits 0 through 3, of the configuration
register make up the boot field.
If the boot field value is 0x0 ( all four bits set to zeros), the router
will enter ROM monitor mode.
If the boot field value is 0x1 (binary 0001), the router will boot from
the image in the ROM.
If the boot field value is 0x2 through 0xF ( binary 0010 through 1111)
the router will follow the normal boot sequence and will look for boot
system commands in the configuration file in NVRAM.
Community String
The Community String is a "password"
that allows either Read Only (RO) or Read/Write (RW) control.
DHCP
Short for Dynamic Host Control Protocol. An effective way to dynamically assign and reuse a fixed number of IP addresses when there are more devices on the network than addresses available. A DHCP server dynamically assigns IP addresses to devices requesting them. These address assignments expire after a time specified by the network manager. The DHCP server then reassigns these addresses to other devices as needed. DHCP is an extension to BOOTP in which the address assignments are static.
DNS
Short for Domain Name System (or Service). The Domain Name System (DNS)
is a distributed Internet directory service. DNS is used mostly to translate
between domain names and IP addresses. Most Internet services rely on
DNS to work, and if DNS fails, web sites cannot be located and email delivery
stalls.
DNS Server
The DNS system consists of three components: DNS data (called resource
records), servers (called name servers) and Internet protocols for fetching
data from the servers.
DNS Name server is a server that runs DNS
server programs containing name-to-IP address mappings, IP address-to-name
mappings, information about the domain tree structure, and other information.
DNS servers also attempt to resolve client queries.
The billions of resource records in the DNS are split into millions of
files called zones. Zones are kept on authoritative servers distributed
all over the Internet, which answer queries based on the resource records
stored in the zones they have copies of. Caching servers ask other servers
for information and cache any replies. Most name servers are authoritative
for some zones and perform a caching function for all other DNS information.
Large name servers are often authoritative for tens of thousands of zones,
but most name servers are authoritative for just a few zones.
Dword Address
A portion of memory, usually a variable,
which has a length of four bytes. The term dword is given to anything
which is four bytes in length. Literally, a dword is a "double word."
For example for the IP Address 206.191.158.55, enter the following keystrokes into the calculator exactly as shown:
206 * 256 + 191 = * 256 + 158 = * 256 +
55
The dword equivalent of the IP address will be the result. In this case, 3468664375.
Errors and Discards
In Performance monitoring Errors and Discards refers to the number of packets that could not be transmitted because of errors which results in discarded packets.
Forward Lookup
Forward DNS (domain name system) Lookup uses an Internet domain name to
find an IP address. When you enter the address for a Web site at your
browser, the address is transmitted to a nearby router which does a forward
DNS lookup in a routing table to locate the IP address. Forward DNS lookup
is the more common lookup since most users think in terms of domain names
rather than IP addresses.
Flash
Memory
A special type of EEPROM (electrically erasable programmable read-only
memory) that can be erased and reprogrammed in blocks instead of one byte
at a time. Many modern PCs have their BIOS stored on a Flash memory chip
so that it can be updated easily if necessary. Such a BIOS is sometimes
called a flash BIOS. Flash memory is also popular in modems because it
enables the modem manufacturer to support new protocols as they become
standardized.
Giants
Giants refers to the number of packets that are discarded by the router because they exceed the medium's maximum packet size.
HEX IP Address
A major numbering system used by computers is hexadecimal or Base 16. In this system, the numbers are counted from 0 to 9 then letters A to F before adding another digit. The letter A through F represent decimal numbers 10 through 15 respectively. The below chart indicates the values of the hexadecimal position compared to 16 raised to a power and decimal values It is much easier to work with large numbers using hexadecimal To convert a value from hexadecimal to binary, you merely translate each hexadecimal digit into its 4-bit binary equivalent. Hexadecimal numbers have either and 0x prefix or an h suffix. For example, the hexadecimal number:
0x3F7A
Translates into, Using the Binary chart and the below chart for Hex:
0011 1111 0111 1010. values than decimal.
DECIMAL |
HEXADECIMAL |
BINARY |
0 |
0 |
0000 |
1 |
1 |
0001 |
2 |
2 |
0010 |
3 |
3 |
0011 |
4 |
4 |
0100 |
5 |
5 |
0101 |
6 |
6 |
0110 |
7 |
7 |
0111 |
8 |
8 |
1000 |
9 |
9 |
1001 |
10 |
A |
1010 |
11 |
B |
1011 |
12 |
C |
1100 |
13 |
D |
1101 |
14 |
E |
1110 |
15 |
F |
1111 |
Hop
Gives the order in which the TCP/IP packets progress from machine to machine,
called the 'distance' (in hops) from the originating machine.
Host Address
A fully qualified domain name (usually alphabetic) identifying the address
of one specific host computer on the Internet. The host address is a subset
of the IP address.
ICMP
Short for Internet Control Message Protocol. ICMP is an extension to the
Internet Protocol (IP) defined by RFC 792. ICMP supports packets containing
error, control, and informational messages. The PING command, for example,
uses ICMP to test an Internet connection.
In Discards
The number of inbound packets which were chosen to be discarded even though no errors had been detected to prevent their being deliverable to a higher-layer protocol. One possible reason for discarding such a packet could be to free up buffer space.
IOS
Short for Internetworking Operating System. The Cisco IOS software is the software that runs on the Cisco products, This platform is integral to the interoperations of network devices in a Cisco internetwork. Cisco IOS includes security, access control, authentication, firewall, encryption, and management services. The main purpose of IOS is to boot the Cisco hardware and begin the optimal transport of data across the internetwork.
IP Address
The 32-bit IP address is often depicted as a dot address that is, four
groups (or quads) of decimal numbers separated by periods. Here's an example:
130.5.5.25
Each of the decimal numbers represents
a string of eight binary digits. Thus, the above IP address really is
this string of 0s and 1s:
10000010.00000101.00000101.00011001
Some portion of the IP address represents
the network number or address and some portion represents the local machine
address (also known as the host number or address). IP addresses can be
one of several classes, each determining how many bits represent the network
number and how many represent the host number. The most common class used
by large organizations (Class B) allows 16 bits for the network number
and 16 for the host number. Using the above example, here's how the IP
address is divided:
<--Network address--><--Host address-->
130.5
.
5.25
If you wanted to add subnetting to this
address, then some portion (in this example, eight bits) of the host address
could be used for a subnet address.
Thus:
<--Network address--><--Subnet address--><--Host address-->
130.5 . 5 . 25
kbps
Short for kilobit per second. One kilobit per second (Kbps) equals 1000 bits per second (bps). Network performance is best measured in bps, but sometimes numbers are given in bytes per second (Bps). Then, one KBps equals one kilobyte per second, one MBps equals one megabyte per second, and GBps equals one gigabyte per second.
Latency
The time delay of data traffic through a network or a switch.
MAC Address
Short for Media Access Control address. MAC Address is a standardized data
link layer address that uniquely identifies each device and is required
for every port or device that connects to a LAN. Other devices in the
network use these addresses to locate specific ports in the network and
to create and update routing tables and data structures. MAC addresses
are 6bytes long and area also known as a hardware address, MAC layer address,
and physical address.
MIB
Short for Management Information Base. MIB is a database of network management
information that is used and maintained by a network management protocol,
such as SNMP or CMIP. The value of a MIB object can be changed or retrieved
using SNMP or CMIP commands, usually through a GUI network management
system. MIB objects are organized in a tree structure that includes public
(standard) and private (proprietary) branches.
Macros
The MIB file can contain one or more MIB modules.
Following are the macros defined in the SMIv1 and SMIv2.
OBJECT IDENTIFIER
OBJECT-TYPE
The following macro definition is defined only in SMIv1.
TRAP-TYPE
The following macro definitions are defined only in SMIv2.
MODULE-IDENTITY
NOTIFICATION-TYPE
OBJECT-IDENTITY
OBJECT-GROUP
AGENT-CAPABILITIES
NOTIFICATION-GROUP
MODULE-COMPLIANCE
TEXTUAL-CONVENTION
Netmask
A netmask is a 32-bit mask used to divide
an IP address into subnets and specify the networks available hosts. In
a netmask two bits are always automatically assigned. For example in 255.255.225.0,
"0" is the assigned network address and in 255.255.255.255,
"255" is the assigned broadcast address. The 0 and 255 are always
assigned and cannot be used.
(http://www.computerhope.com/jargon/n/netmask.htm)
Network Classes
Class
A Network - binary address starts with 0, therefore the decimal
number can be anywhere from 1 to 126. The first 8 bits (the first octet)
identify the network and the remaining 24 bits indicate the host within
the network. An example of a Class A IP address is 102.168.212.226, where
"102" identifies the network and "168.212.226" identifies
the host on that network.
Class
B Network - binary addresses starts with 10, therefore the decimal
number can be anywhere from 128 to 191. (The number 127 is reserved for
loopback and is used for internal testing on the local machine.) The first
16 bits (the first two octets) identify the network and the remaining
16 bits indicate the host within the network. An example of a Class B
IP address is 168.212.226.204 where "168.212" identifies the
network and "226.204" identifies the host on that network.
Class
C Network - binary addresses starts with 110, therefore the decimal
number can be anywhere from 192 to 223. The first 24 bits (the first three
octets) identify the network and the remaining 8 bits indicate the host
within the network. An example of a Class C IP address is 200.168.212.226
where "200.168.212" identifies the network and "226"
identifies the host on that network.
Class
D Network - binary addresses starts with 1110, therefore the decimal
number can be anywhere from 224 to 239. Class D networks are used to support
multicasting.
Class
E Network -- binary addresses start with 1111, therefore the decimal
number can be anywhere from 240 to 255. Class E networks are used for
experimentation. They have never been documented or utilized in a standard
way.
NIC
Short for Network Interface Card. A network
interface card (NIC) is a computer circuit board or card that is installed
in a computer so that it can be connected to a network. Personal computers
and workstations on a local area network (LAN) typically contain a network
interface card specifically designed for the LAN transmission technology,
such as Ethernet or Token Ring. Network interface cards provide a dedicated,
full-time connection to a network.
NVRAM
Short for nonvolatile RAM. NVRAM is a special memory that does not lose its information when a router is powered off. It stores the system's startup configuration file and the virtual configuration register.
Octet Flow
In network monitoring the term Octet flow refers to the number of octets transmitted over the interface.
OID
Short for Object Identifier. The OID is a long numeric tag, used to distinguish each variable uniquely in the MIB and in SNMP messages.
Out Discards
The number of outbound packets which were chosen to be discarded even though no errors had been detected to prevent their being transmitted. One possible reason for discarding such a packet could be to free up buffer space.
Packet Flow
A flow is a set of packets passing an observation point in the network during a certain time interval. All packets belonging to a particular flow have a set of common properties derived from the data contained in the packet and from the packet treatment at the observation point.
QoS
Quality of Service standards seek to maximize the use of available network bandwidth by prioritizing time-sensitive traffic.
RAM
Short for random-access memory. RAM is a volatile memory that can be read and written by a computer.
Received Errors
The number of inbound packets that contained errors preventing them from being deliverable to a
higher-layer protocol.
Reverse
Lookup
Reverse DNS lookup uses an Internet IP address to find a domain name.
Round Trip Time
The Round Trip time refers to the timestamp placed by Ping in each packet, which is echoed back to calculate how long each packet exchange took.
Router
A router is an Intermediate System (IS) which operates at the network layer
of the OSI reference model. Routers may be used to connect two or more
IP networks, or an IP network to an internet connection.
A router consists of a computer with at least two network interface cards supporting the IP protocol. The router receives packets from each interface via a network interface and forwards the received packets to an appropriate output network interface.
A router introduces delay (latency) as it processes the packets it receives. The total delay observed is the sum of many components including:
Time taken to process the frame by the data link protocol
Time taken to select the correct output link (i.e. filtering and routing)
Queuing delay at the output link (when the link is busy)
Other activities which consume processor resources (computing routing tables, network management, generation of logging information)
The router queue of packets waiting to be sent also introduces a potential cause of packet loss. Since the router has a finite amount of buffer memory to hold the queue, a router which receives packets at too high a rate may experience a full queue. In this case, the router has no other option than to simply discard excess packets. If required, these may later be re-transmitted by a transport protocol.
ROM
Short for read-only memory. ROM is the non volatile memory that can be read , but not written , by the computer. The image in ROM is the image the router first uses when it is powered up. This image is usually an older and smaller version of IOS without the features of a full IOS version.
Runts
Runts refers to the number of packets that are discarded because they are smaller than the medium's minimum packet size.
SNMP Agent
A management entity consisting of hardware and embedded software which responds to SNMP requests over Ethernet from an SNMP manager
Subnet
A subnet (short for "subnetwork") is an identifiably separate part of an organization's network. Typically, a subnet may represent all the machines at one geographic location, in one building, or on the same local area network (LAN). Having an organization's network divided into subnets allows it to be connected to the Internet with a single shared network address. Without subnets, an organization could get multiple connections to the Internet, one for each of its physically separate subnet, but this would require an unnecessary use of the limited number of network numbers the Internet has to assign. It would also require that Internet routing tables on gateways outside the organization would need to know about and have to manage routing that could and should be handled within an organization.
The Internet is a collection of networks
whose users communicate with each other. Each communication carries the
address of the source and destination networks and the particular machine
within the network associated with the user or host computer at each end.
This address is called the IP address (Internet Protocol address). This
32-bit IP address has two parts: one part identifies the network (with
the network number) and the other part identifies the specific machine
or host within the network (with the host number). An organization can
use some of the bits in the machine or host part of the address to identify
a specific subnet. Effectively, the IP address then contains three parts:
the network number, the subnet number, and the machine number.
(adapted from searchNetworking.com)
Subnet Mask
A subnet mask is used to determine what subnet an IP address belongs to.
SMTP
Internet protocol providing e-mail services.
TCP/IP
TCP/IP - Stands for "Transmission Control Protocol / Internet Protocol" - TCP/IP is a suite of communications protocols that forms the basis for and defines the Internet.
Transmitted Errors
The number of outbound packets that could not be transmitted because of errors.
TTL
Short for Time to Live. TTL
is a field
in the Internet Protocol (IP) that specifies how many more hops a packet
can travel before being discarded or returned.
Timeout
Timeout is the value to be set in milliseconds to wait for each packet
reply before the connection is disconnected as no data is being sent.
UDP
A communications protocol that, like TCP, runs on top of IP networks. Unlike
TCP/IP, UDP/IP provides very few error recovery services, offering instead
a direct way to send and receive datagrams (a datagram is the term used
to describe data that is packetised for network transport) typically over
an IP network. It is used primarily for broadcasting messages over a network.
UDP uses the Internet Protocol to get data from one computer or device
to another but does not divide a message into sequenced packets nor reassemble
it at the other end.
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