Glossary

Glossary
 
 
 
 
 
 
Authentication The process by which a user’s identity is checked within the network to ensure that the user has access to the requested resources.
 
Basic In/Out System Chips on the motherboard of a computer contain read only
(BIOS) memory instructions that are used to start up a computer. The operating system of a PC also makes use of BIOS instructions and settings to access hardware components such as a disk drive. Some BIOS/CMOS settings can be set to scan for viruses, causing problems for some installation programs.
 
Baud Rate The baud rate is a measure of the number of symbols (characters) transmitted per unit of time. Each symbol will normally consist of a number of bits, so the baud rate will only be the same as the bit rate when there is one bit per symbol. The term originated as a measure for the transmission of telegraph characters. It has little application today except in terms of modem operation. It is recommended that all data rates are referred to in bps, rather than baud (which is easy to misunderstand). Additionally, baud rate cannot be equated to bandwidth unless the number of bits per symbol is known.
 
BogoMips BogoMips (from "bogus" and MIPS). Unscientific measurement of CPU speed made by the Linux kernel when it boots to calibrate an internal busy-loop.
 
Bonding (Linux) Ability to detect communication failure transparently, and switch from one LAN connection to another. The Linux bonding driver has the ability to detect link failure and reroute network traffic around a failed link in a manner transparent to the application. It also has the ability (with certain network switches) to aggregate network traffic in all working links to achieve higher throughput. The bonding driver accomplishes this by enslaving all of the Ethernet ports in the bond to the same Ethernet MAC address, which ensures the proper routing of packets across the links.
Boot To start a computer so that it is ready to run programs for the user. A PC can be booted either by turning its power on, (Cold Boot) or by pressing Ctrl+Alt+Del (Warm Boot).
 
Break Signal A break signal is a logical zero on a TXD or RXD lines for a period of time, usually 250 to 500 milliseconds. Normally a receive or transmit data signal stays at the mark (on=1) voltage until the next character is transferred. A Break is sometimes used to reset the communications line or change the operating mode of communications hardware. Breaks at a serial console port are interpreted by Sun servers as a signal to suspend operation and switch to monitor mode.
 
Checksum A computed value which depends on the contents of a block of data and which is transmitted or stored along with the data in order to detect corruption of the data. The receiving system recomputes the checksum based upon the received data and compares this value with the one sent with the data. If the two values are the same, the receiver has some confidence that the data was received correctly.
CIDR Notation Classless Inter Domain Routing (CIDR) is a method for
assigning IP addresses without using the standard IP
address classes like Class A, Class B or Class C.
In CIDR notation, an IP address is represented as A.B.C.D /n, where "/n" is called the IP prefix or network prefix. The IP prefix identifies the number of significant bits used to identify a network. For example, 192.9.205.22 /18 means, the first 18 bits are used to represent the network and the remaining 14 bits are used to identify hosts. Common prefixes are 8, 16, 24, and 32.
 
CLI Command line interface. An interface that allows use of text commands. Through CLI, individual commands can be given to the computer one at a time using the keyboard. Cyclades products run the Linux operating system, and most Cyclades products provide CLI access. Administrators type "CLI" on the command line of the Linux shell. The Cyclades CLI tool provides many commands and nested parameters in a format called the CLI parameter tree.
Cluster A cluster is a group of one or more computers working as a group to execute a certain task. From the user standpoint, a cluster acts as a large computer system.
 
Console Access Server (CAS)
A CAS has an Ethernet LAN connection and many RS-232 serial ports. It connects to the console ports of servers and networking equipment and allows convenient and secure access from a single location.
 
Community The community name acts as a password and is used to authenticate messages sent between an SNMP client and a router containing an SNMP server. The community name is sent in every packet between the client and the server.
 
Console Terminal used to configure network devices at boot (start-up) time. Also used to refer to the keyboard, video and mouse user interface to a server.
 
Console Port Most of the equipment in a data center (servers, routers, switches, UPS, PBX, etc.) has a serial console port for out-of-band management purposes.
 
DHCP Dynamic Host Configuration Protocol. A protocol for automatic TCP/IP configuration that provides static and dynamic address allocation and management.
DHCP enables individual computers on an IP network to extract their configurations from a server (the 'DHCP server') or servers, in particular, servers that have no exact information about the individual computers until they request the information. The overall purpose of this is to reduce the work necessary to administer a large IP network. The most significant piece of information distributed in this manner is the IP address.
 
DNS Server Domain Name Server. The computer you use to access the DNS to allow you to contact other computers on the Internet. The server keeps a database of host computers and their IP addresses.
 
Domain Name The unique name that identifies an Internet site. Domain Names always have 2 or more parts, separated by dots. The part on the left is the most specific, and the part on the right is the most general. A given machine may have more than one Domain Name but a given Domain Name points to only one machine. For example, the domain names: matisse.net, mail.matisse.net, workshop.matisse.net can all refer to the same machine, but each domain name can refer to no more than one machine. Usually, all of the machines on a given Network will have the same thing as the right-hand portion of their Domain Names (matisse.net in the examples above). It is also possible for a Domain Name to exist but not be connected to an actual machine. This is often done so that a group or business can have an Internet e-mail address without having to establish a real Internet site. In these cases, some real Internet machine must handle the mail on behalf of the listed Domain Name.
 
Escape Sequence A sequence of special characters that sends a command to a device or program. Typically, an escape sequence begins with an escape character, but this is not universally true.
 
An escape sequence is commonly used when the computer and the peripheral have only a single channel in which to send information back and forth. If the device in question is "dumb" and can only do one thing with the information being sent to it (for instance, print it) then there is no need for an escape sequence. However most devices have more than one capability, and thus need some way to tell data from commands.
 
Ethernet A LAN cable-and-access protocol that uses twisted-pair or coaxial cables and CSMA/CD (Carrier Sense Multiple Access with Collision Detection), a method for sharing devices over a common medium. Ethernet runs at 10 Mbps; Fast Ethernet runs at 100 Mbps. Ethernet is the most common type of LAN.
 
Flash Flash refers to a type of memory that can be erased and reprogrammed in units of memory known as blocks rather than one byte at a time; thus, making updating to memory easier.
 
Flow Control A method of controlling the amount of data that two devices exchange. In data communications, flow control prevents one modem from "flooding" the other with data. If data comes in faster than it can be processed, the receiving side stores the data in a buffer. When the buffer is nearly full, the receiving side signals the sending side to stop until the buffer has space again. Between hardware (such as your modem and your computer), hardware flow control is used; between modems, software flow control is used.
 
FTP Short for File Transfer Protocol. The protocol for exchanging files over the Internet. FTP works in the same way as HTTP for transferring web pages from a server to a user's browser. FTP uses the Internet's TCP/IP protocols to enable data transfer.
Hot-Swap Ability to remove and add hardware to a computer system without powering off the system.
 
ICMP Internet Control Message Protocol is an Internet protocol sent in response to errors in TCP/IP messages. It is an error
reporting protocol between a host and a gateway. ICMP uses Internet Protocol (IP) datagrams (or packets), but the messages are processed by the IP software and are not directly apparent to the application user.
 
In-band Network In a computer network, when the management data is
Management accessed using the same network that carries the data, this is called “in-band management.”
 
IP Address A 32-bit address assigned to hosts using TCP/IP. It belongs to one of five classes (A-E) and is expressed as 4 octets separated by periods formatted as dotted decimals.
 
Each address has a network number, an optional sub network number and a host number. The first two numbers are used for routing, while the host number addresses an individual host within the network or sub network. A subnet mask is used to extract network and sub network information from the IP address.
 
IP packet filtering This is a set of facilities in network equipment that allows the filtering of data packets based on source/destination addresses, protocol, TCP port number and other parameters. Packet filtering is one of the main functions of a firewall.
 
IPsec Short for IP Security Protocol, IPsec is an extended IP protocol that provides encrypted security services. These services enable authentication, as well as for access and trustwothiness control. IPsec provides similar services as SSL, but it works on a network layer. Through IPsec you can create encrypted tunnels (VPN) or encrypt traffic between two hosts.
 
ISDN A set of communications standards allowing a single wire or optical fibre to carry voice, digital network services and video. ISDN is intended to eventually replace the plain old telephone system.
 
Kerberos Kerberos was created by MIT as a solution to network security problems. The Kerberos protocol uses strong cryptography so that a client can prove its identity to a server (and vice versa) across an insecure network connection. It works by assigning a unique key called a ticket to each user that logs on to the network. The ticket is then embedded in messages to identify the sender of the message.
After a client and server has used Kerberos to prove their identity, they can also encrypt all of their communications to assure privacy and data integrity as they go about their business.
 
LDAP Lightweight Directory Access Protocol. A software protocol for enabling anyone to locate organizations, individuals, and other resources such as files and devices in a network, whether on the Internet or on a corporate intranet.
LDAP is a "lightweight" (smaller amount of code) version of DAP (Directory Access Protocol), which is part of X.500, a standard for directory services in a network.
MAC Medium Access Control. Internationally unique hardware identification address that is assigned to the NIC (Network Interface Card) which interfaces the node to the LAN.
 
Masquerading Where a system acts on behalf of other systems, such as when an ISP server accesses network services on behalf of a dial-up user.
 
MTU Short for Maximum Transmission Unit, the largest physical packet size, measured in bytes, that a network can transmit. Any messages larger than the MTU are divided into smaller packets before being sent.
Every network has a different MTU, which is set by the network administrator. On Windows, you can set the MTU of your machine. This defines the maximum size of the packets sent from your computer onto the network. Ideally, you want the MTU to be the same as the smallest MTU of all the networks between your machine and a message's final destination. Otherwise, if your messages are larger than one of the intervening MTUs, they will get broken up (fragmented), which slows down transmission speeds.
Trial and error is the only sure way of finding the optimal MTU, but there are some guidelines that can help. For example, the MTU of many PPP connections is 576, so if you connect to the Internet via PPP, you might want to set your machine's MTU to 576 too. Most Ethernet networks, on the other hand, have an MTU of 1500.
 
NEBS NEBS (Network Equipment Building Systems) Compliance means that equipment has been tested and proven to meet the NEBS requirements commonly adhered to by several telecommunications carriers. The requirements are in place to ensure that telecommunications equipment poses no risk or safety hazard to people, nearby equipment, or to the physical location where the equipment operates, and that equipment is reliable and dependable during both normal and abnormal conditions. Tests address heat release, surface temperature, fire resistance, electomagnetic compatibility, electrical safety, and manufacturing component characteristics, among other attributes.
 
Network Mask A 32-bit number used to group IP addresses together or to indicate the range of IP addresses on a single IP network/subnet/supernet. There is a group of addresses assigned to each network segment. For example, the mask 255.255.255.0 groups together 254 IP addresses. If we have, as another example, a sub-network 192.168.16.64 with mask 255.255.255.224, the addresses we may assign to computers on the sub-network are 192.168.16.65 to 192.168.16.94, with a broadcast address of 192.168.16.95.
A number used by software to separate the local subnet address from the rest of a given Internet protocol address
Network masks divide IP addresses into two parts (network address and address of a particular host within the network). Mask have the same form as IP addresses (i.e. 255.255.255.0), however, its value is needed to be understood as a 32-bit number with certain number of ones on the left end and zeros as the rest. The mask cannot have an arbitrary value. The primary function of a subnet mask is to define the number of IP hosts that participate in an IP subnet. Computers in the same IP subnet should not require a router for network communication.
NFS Network File System is a protocol suite developed and licensed by Sun Microsystems that allows different makes of computers running different operating systems to share files and disk storage. NFS is implemented using a connectionless protocol (UDP) in order to make it stateless.
NTP Network Time Protocol. A standard for synchronizing your system clock with the ``true time'', defined as the average of many high-accuracy clocks around the world.
Object Identifiers (OID) The SNMP manager or the management application uses a well-defined naming syntax to specify the variables to the SNMP agent. Object names in this syntax are called Object Identifiers (Object IDs or OIDs). OIDs are series of numbers that uniquely identify an object to an SNMP agent. OIDs are arranged in a hierarchical, inverted tree structure.
The OID tree begins with the root and expands into branches. Each point in the OID tree is called a node and each node will have one or more branches, or will terminate with a leaf node. The format of OID is a sequence of numbers with dots in between.
There are two roots for Object Identifiers, namely iso and ccit. iso starts with.1 and ccit starts with.0. Most Object Identifiers start with.1.3.6.1, where 1=iso, 3=org, 6= dod,
1 = internet. The Internet sub-tree branches into mgmt and private.
To understand the concept of relative and absolute Object Identifiers, let us consider the AdventNet Object Identifier.1.3.6.1.4.1.2162. It specifies the path from the root of the tree. The root does not have a name or a number but the initial 1 in this OID is directly below root. This is called an absolute OID. However, a path to the variable may be specified relative to some node in the OID tree. For example, 2.1.1.7 specifies the sysContact object in the system group, relative to the Internet (.1.3.6.1) node in the OID tree. This is called a relative OID.
Off-Line Data Buffering This is a CAS feature that allows capture of console data even when there is no one connected to the port.
OID See Object Identifier.
OOBI Out-of-Band Infrastructure, an integrated systems approach to remote administration. Consists of components that provide secure, alternate path to connect to and manage an organization’s production network remotely.
Packet A packet is a basic communication data unit used when transmitting information from one computer to another. The maximum length of a packet depends on the communication medium. As an example, in Ethernet networks the maximum length is1500 bytes. A data packet can be divided into two parts: the header part and the data part. The header contains information needed for communication between nodes; the data is the body of the packet that is ultimately received by the application.
Parity In serial communications, the parity bit is used in a simple error detection algorithm. As a stream of data bits is formed, an extra bit, called the parity bit, is added. This bit is set on (1) or off (0), depending on the serial communications parameters set in the UART chip.
The following lists the available parity parameters and their meanings:
Odd - Parity bit set so that there is an odd number of 1 bits
Even - Parity bit set so that there is an even number of 1 bits
None - Parity bit is ignored, value is indeterminate
PCMCIA Personal Computer Memory Card International Association. An organization consisting of some 500 companies that has developed a standard for small, credit card-sized devices, called PC Cards. Originally designed for adding memory to portable computers, the PCMCIA standard has been expanded several times and is now suitable for many types of devices including network cards (NICs).
The PCMCIA 2.1 Standard was published in 1993. As a result, PC users can be assured of standard attachments for any peripheral device that follows the standard.
Port A port is a 16-bit number (the allowed range being 1 through 65535) used by the TCP and UDP protocols at the transport layer. Ports are used to address applications (services) that run on a computer. If there was only a single network application running on the computer, there would be no need for port numbers and the IP address only would suffice for addressing services. However, several applications may run at once on a particular computer and we need to differentiate among them. This is what port numbers are used for. Thus, a port number may be seen as an address of an application within the computer.
PPP Point-to-Point Protocol. This protocol is a way to connect your computer to the Internet over telephone lines. PPP is replacing an older protocol, SLIP, as it is more stable and has more error-checking features.
PPP has been a widely-used Internet standard for sending datagrams over a communications link. The PPP standard is described in RFC 1661 by the Point-to-Point Working Group of the Internet Engineering Task Force (IETF). PPP is commonly used when remote computers call an Internet service provider (ISP) or a corporate server that is configured to receive incoming calls.
Profile Usage setup of the ACS either as a Console Access Server (CAS), a Terminal Server, or a Remote Access Server.
RADIUS Remote Authentication Dial-In User Service is a client/server protocol and software that enables remote access servers to communicate with a central server to authenticate dial-in users and authorize their access to the requested system or service. RADIUS allows a company to maintain user profiles in a central database that all remote servers can share.
RISC Reduced Instruction Set Computer. This describes a computer processor architecture that uses a reduced set of instructions (and achieves performance by executing those instructions very fast.) Most UNIX servers (Sun Sparc, HP, IBM RS6000, Compaq Alpha) were designed with a processor using a RISC architecture. The Intel ® x86 architecture.
Root Access Root is the term for a very highly privileged administrative user (particularly in Unix environments). When an ISP grants you root access, it means you will have full control of the server. With full control, you will be able to install any software and access any file on that server.
Routing Table The Routing Table defines which interface should transmit an IP packet based on destination IP information.
RPC Short for Remote Procedure Call. A type of protocol that allows a program on one computer to execute a program on a server. Using RPC, a system developer do not need to develop specific procedures for the server. The client program sends a message to the server with appropriate arguments and the server returns a message containing the results of the program executed.
Secure Shell (SSH) SSH has the same functionality as Telnet (see definition for Telnet), but adds security by encrypting data before sending it through the network.
Server Farm A collection of servers running in the same location (see Cluster).
SMTP Simple Mail Transfer Protocol. Specifies the format of messages that an SMTP client on one computer can use to send electronic mail to an SMTP server on another computer.
SNMP Short for Simple Network Management Protocol, a set of protocols for managing complex networks. The first versions of SNMP were developed in the early 80s. SNMP works by sending messages, called protocol data units (PDUs), to different parts of a network.
SNMP-compliant devices, called agents, store data about themselves in Management Information Bases (MIBs) and return this data to the SNMP requesters.
(Source: Webopedia)
SNMP Traps Notifications or Event Reports are occurrences of Events in a Managed system, sent to a list of managers configured to receive Events for that managed system. These Event Reports are called Traps in SNMP. The Traps provide the value of one or more instances of management information.
Any SNMP enabled Device generates Fault Reports (Traps) that are defined in the MIB (which the SNMP Agent has implemented).
The Trap Definition vary with the SNMP Version (which defines the messaging format), but the information contained in these are essentially identical. The major difference between the two message formats is in identifying the events.
Stop Bit A bit which signals the end of a unit of transmission on a serial line.A stop bit may be transmitted after the end of each byte or character.
Subnet Mask A bit mask used to select bits from an Internet address for subnet addressing. Also known as Address Mask.
SSH (Secure Shell) A protocol which permits secure remote access over a network from one computer to another. SSH negotiates and establishes an encrypted connection between an SSH client and an SSH server.
STTY Set the options for a terminal device interface.
This command prints information about your terminal settings. The information printed is the same as if you had typed stty while interacting with a shell.
The stty utility sets or reports on terminal I/O characteristics for the device that is its standard input. Without options or operands specified, it reports the settings of certain
characteristics, usually those that differ from implementation-dependent defaults. Otherwise, it modifies the terminal state according to the specified operands.
TACACS Terminal Access Controller Access Control System.
Authentication protocol, developed by the DDN community, that provides remote access authentication and related services, such as event logging. User passwords are administered in a central database rather than in individual routers, providing an easily scalable network security solution.
TACACS+ Terminal Access Controller Access Control System Plus. A protocol that provides remote access authentication, authorization, and related accounting and logging services commonly used in UNIX networks.
TCP Keep-Alive Interval The time interval between the periodic polling of all inactive TCP/IP connections, checking that the client processes really are still there. After a certain period of inactivity on an established connection, the server's TCP/IP software will begin to send test packets to the client, which must be acknowledged. After a preset number of 'probe' packets has been ignored by the client, the server assumes the worst and the connection is closed.
The keep-alive timer provides the capability to know if the client's host has either crashed and is down or crashed and rebooted.
Telnet A terminal emulation program for TCP/IP networks such as the Internet. The Telnet program runs on your computer and connects your PC to a server on the network. You can then enter commands through the Telnet program and they will be executed as if you were entering them directly on the server console
Terminal Server A terminal server has one Ethernet LAN port and many
RS-232 serial ports. It is used to connect many terminals to the network. Because they have the same physical interfaces, terminal servers are sometimes used as console access servers.
TTY 1. In Unix, refers to any terminal; sometimes used to refer to the particular terminal controlling a given job (it is also the name of a Unix command which outputs the name of the current controlling terminal). 2. Also in Unix, any serial port, whether or not the device connected to it is a terminal; so called because under Unix such devices have names of the form tty.
UDP User Datagram Protocol uses a special type of packet called a datagram. Datagrams do not require a response; they are one way only (connectionless). Datagrams are usually used for streaming media because an occasional packet loss will not affect the final product of the transmission.
U Rack Height Unit A standard computer rack has an internal width of 17 inches. Rack space on a standard rack is measured in units of height (U). One U is 1.75 inches. A device that has a height of 3.5 inches takes 2U of rack space.
VPN Virtual Private Networking allows local area networks to communicate across wide area networks, typically over an encrypted channel. See also: IPsec.
Watchdog Timer A watchdog timer (WDT) is a device or electronic card that performs a specific operation after a certain period of time if something goes wrong with an electronic system and the system does not recover on its own.
A common problem is for a machine or operating system to lock up if two parts or programs conflict, or, in an operating system, if memory management trouble occurs. In some cases, the system will eventually recover on its own, but this may take an unknown and perhaps extended length of time.
A watchdog timer can be programmed to perform a warm boot (restarting the system) after a certain number of seconds during which a program or computer fails to respond
following the most recent mouse click or keyboard action.
The timer can also be used for other purposes, for example, to actuate the refresh (or reload) button in a Web browser if a Web site does not fully load after a certain length of time following the entry of a Uniform Resource Locator (URL).
 

Glossary