Authentication, authorization, and accounting. A system in IP-based networking to control which computer resources specific users can access and to keep track of the activity of specific users over the network.


Area border router. In OSPF, an ABR has interfaces in multiple areas, and it is responsible for exchanging summary advertisements with other ABRs.


Access Control List. A mechanism for filtering packets at the hardware level. Packets can be classified by characteristics such as the source or destination MAC, IP addresses, IP type, or QoS queue. Once classified, the packets can be forwarded, counted, queued, or dropped.


Asynchronous Chassis Management Interface.

ad-hoc mode

An 802.11 networking framework in which devices or stations communicate directly with each other, without the use of an access point (AP).


Advanced Encryption Standard. AES is an algorithm for encryption that works at multiple network layers simultaneously. As a block cipher, AES encrypts data in fixed-size blocks of 128 bits; AES is also a privacy transform for IPSec and Internet Key Exchange (IKE). Created by the National Institute of Standards and Technology (NIST), the standard has a variable key length—it can specify a 128-bit key (the default), a 192-bit key, or a 256-bit key.

For the WPA2/802.11i implementation of AES, a 128-bit key length is used. AES encryption includes four stages that make up one round. Each round is then iterated 10, 12, or 14 times depending upon the bit-key size. For the WPA2/802.11i implementation of AES, each round is iterated 10 times.


Advanced Encryption Standard - Counter-Mode/CBC-MAC Protocol. CCM is a new mode of operation for a block cipher that enables a single key to be used for both encryption and authentication. The two underlying modes employed in CCM include Counter mode (CTR) that achieves data encryption and Cipher Block Chaining Message Authentication Code (CBC-MAC) to provide data integrity.

alternate port

In RSTP, the alternate port supplies an alternate path to the root bridge and the root port.

AP (access point)

In wireless technology, access points are LAN transceivers or "base stations" that can connect to the regular wired network and forward and receive the radio signals that transmit wireless data.


In OSPF, an area is a logical set of segments connected by routers. The topology within an area is hidden from the rest of the autonomous system (AS).


Address Resolution Protocol. ARP is part of the TCP/IP suite used to dynamically associate a device's physical address (MAC address) with its logical address (IP address). The system broadcasts an ARP request, containing the IP address, and the device with that IP address sends back its MAC address so that traffic can be transmitted.


Autonomous system. In OSPF, an AS is a connected segment of a network topology that consists of a collection of subnetworks (with hosts attached) interconnected by a set of routes. The subnetworks and the routers are expected to be under the control of a single administration. Within an AS, routers may use one or more interior routing protocols and sometimes several sets of metrics. An AS is expected to present to other autonomous systems an appearance of a coherent interior routing plan and a consistent picture of the destinations reachable through the AS. An AS is identified by a unique 16-bit number.


Autonomous system border router. In OSPF, an ASBR acts as a gateway between OSPF and other routing protocols or other autonomous systems.


A connection between a wireless device and an access point.


See ATM.


Asynchronous transmission mode. A start/stop transmission in which each character is preceded by a start signal and followed by one or more stop signals. A variable time interval can exist between characters. ATM is the preferred technology for the transfer of images.


In STP, autobind (when enabled) automatically adds or removes ports from the STPD. If ports are added to the carrier VLAN, the member ports of the VLAN are automatically added to the STPD. If ports are removed from the carrier VLAN, those ports are also removed from the STPD.


As set forth in IEEE 802.3u, autonegotation allows each port on the switch—in partnership with its link partner—to select the highest speed between 10 Mbps and 100 Mbps and the best duplex mode.