ICND 1

access control 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). 

Rating of the trustworthiness of a routing information source. Administrative distance often is expressed as a numerical value between 0 and 255. The higher the value, the lower the trustworthiness rating. 

African Network Information Center. AfriNIC is the Regional Internet Registry (RIR) for Africa. They are responsible for the distribution and management of Internet number resources (such as IP addresses and ASN Numbers) for the African region. 

Authentication Header. A security protocol that provides data authentication and optional antireplay services. AH is embedded in the data to be protected (a full IP datagram). 

In anycast routing, the IP packet is sent to the topologically nearest host. 

access point. A node on a wireless network that allows other wireless devices to connect to a wired network. 

application programming interface. The means by which an application program talks to communications software. Standardized APIs allow application programs to be developed independently of the underlying method of communication. A set of standard software interrupts, calls, and data formats that computer application programs use to initiate contact with other devices (for example, network services, mainframe communications programs, or other programtoprogram communications). Typically, APIs make it easier for software developers to create the links that an application needs to communicate with the operating system or with the network. 

Asia Pacific Network Information Center. Nonprofit Internet registry organization for the Asia Pacific region. The other Internet registries are currently IANA, RIPE NCC, and InterNIC. 

American Registry for Internet Numbers. A nonprofit organization that administers and registers IP numbers for the geographical areas that are currently managed by Network Solutions (InterNIC). Those areas include, but are not limited to, North America, South America, South Africa, and the Caribbean. 

Address Resolution Protocol. Internet protocol that is used to map an IP address to a MAC address. Defined in RFC 826. 

autonomous system. A collection of networks under a common administration sharing a common routing strategy. Autonomous systems are subdivided by areas. An autonomous system must be assigned a unique 16bit number by the IANA. 

American Standard Code for Information Interchange. An 8bit code for character representation (7 bits plus parity). 

Asynchronous Transfer Mode. The international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixedlength (53byte) cells. Fixedlength cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of highspeed transmission media, such as E3, SONET, and T3. 

auxiliary. 

Border Gateway Protocol. Interdomain routing protocol that replaces EGP. BGP exchanges reachability information with other BGP systems. It is defined by RFC 1163. 

burnedin address. Refers to the burnedin MAC address. 

A special address that is reserved for sending a message to all stations. Generally, a broadcast address is a MAC destination address of all 1s. 

contentaddressable memory. 

cable television. A communication system where multiple channels of programming material are transmitted to homes using broadband coaxial cable. Formerly called Community Antenna Television. 

classless interdomain routing. Technique supported by BGP4 and based on route aggregation. CIDR allows routers to group routes to reduce the quantity of routing information carried by the core routers. With CIDR, several IP networks appear to networks outside the group as a single, larger entity. With CIDR, IP addresses and their subnet masks are written as four octets, separated by periods, followed by a forward slash and a twodigit number that represents the subnet mask. 

Common Internet File System. 

class of service. An indication of how an upperlayer protocol requires a lowerlayer protocol to treat its messages. In SNA subarea routing, CoS definitions are used by subarea nodes to determine the optimal route to establish a given session. A CoS definition comprises a virtual route number and a transmission priority field. Also called ToS. 

customer premises equipment. Terminating equipment such as terminals, telephones, and modems supplied by the telephone company, installed at customer sites, and connected to the telephone company network. Can also refer to any telephone equipment residing on the customer site. 

Carrier Sense Multiple Access with Collision Detection. Mediaaccess mechanism wherein 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. Ethernet and IEEE 802.3 use CSMA/CD access. 

destination address. 

Data Center Bridging Exchange. 

Dynamic Domain Name System. 

Dynamic Host Configuration Protocol (common term). Provides a mechanism for allocating IP addresses dynamically so that addresses can be reused when hosts no longer need them. 

Domain Name System. System used on the Internet for translating names of network nodes into addresses. 

DataoverCable Service Interface Specifications. Defines technical specifications for equipment at both subscriber locations and cable operator headends. 

The DORA process in DHCP works as follows: D > Discover O > Offer R > Request A > Acknowledgment 

denial of service. An intentional or unintentional attack on a device that makes the resource unavailable to perform its normal function. 

Disk Operating System. MSDOS is the original operating system for the PC from Microsoft Corporation. 

Dynamic Trunking Protocol.