CCIE

AAA
AAA See Authentication, authorization, and accounting.
AAAA In IPv6 DNS, the IPv6 equivalent of an IPv4 DNS A record.
ABR See Area Border Router.
Access Control Entry An individual line in an ACL.
Access Control Server A term referring generically to a server that performs many AAA functions. It also refers to the software product Cisco Secure Access Control Server.
access link In Frame Relay, a link between a router and a Frame Relay switch.
access rate The speed at which the access link is clocked. This choice affects the price of the connection and many aspects of traffic shaping and policing, compression, quality of service, and other configuration options.
ACE See Access Control Entry.
Ack (EIGRP) An EIGRP message that is used to acknowledge reliable EIGRP messages, namely Update, Query, and Reply messages. Acks do not require an Ack.
ACS See Access Control Server.
active (EIGRP) A state for a route in an EIGRP topology table that indicates that the router is actively sending Query messages for this route, attempting to validate and learn the current best route to that subnet.
active mode FTP Defines a particular behavior for FTP regarding the establishment of data TCP connections. In active mode, the FTP client uses the FTP PORT command, over the FTP control connection, to tell the FTP server the port on which the client should be listening for a new data connection. The server uses well-known port 20, and initiates a TCP connection to the FTP client’s earlier-declared port.
active scanning Each 802.11 station periodically sends a probe request frame on each RF channel and monitors probe response frames that all access points within range send back. Stations use the signal strength of the probe response frames to determine which access point or ad hoc network to associate with.
actual queue depth The actual number of packets in a queue at a particular time.
ad hoc mode A wireless LAN that only includes wireless users and no access points. 802.11 data frames in an ad hoc network travel directly between wireless users.
adaptive shaping 847
adaptive shaping A Frame Relay traffic shaping feature during which the shaping rate is reduced when the shaper notices congestion through the receipt of BECN or ForeSight messages.
Address Resolution Protocol Defined in RFC 826, a protocol used on LANs so that an IP host can discover the MAC address of another device that is using a particular IP address.
adjacency (EIGRP) Often used synonymously with neighbor, but with emphasis on the fact that all required parameters match, allowing routing updates to be exchanged between the routers.
adjacency table A table used by CEF that holds information about adjacent IP hosts to which packets can be forwarded.
adjacent (OSPF) Any OSPF neighbor for which the database flooding process has completed.
adjacent-layer interaction On a single computer, one layer provides a service to a higher layer. The software or hardware that implements the higher layer requests that the next lower layer perform the needed function.
administrative scoping Controls the distribution of multicast traffic for the private multicast address range 239.0.0.0 to 239.255.255.255 by configuring a filter and applying it on the interfaces.
administrative weight A Cisco-proprietary BGP feature. The administrative weight can be assigned to each NLRI and path locally on a router, impacting the local router’s choice of the best BGP routes. The value cannot be communicated to another router.
administratively scoped addresses The range 239.0.0.0 through 239.255.255.255 that IANA has assigned for use in private multicast domains.
Advanced Encryption Standard A superior encryption mechanism that is part of the 802.11i standard and has much stronger security than TKIP.
advertised window See receiver’s advertised window.
AES See Advanced Encryption Standard.
AF See Assured Forwarding.
aggregatable global unicast address An IPv6 address format used for publicly registered IPv6 addresses.
aggregate route Another term for summary route.
848 AGGREGATOR
AGGREGATOR An optional transitive BGP path attribute that, for a summary route, lists the BGP RID and ASN of the router that created the summary.
AIS Alarm Indication Signal. With T1s, the practice of sending all binary 1s on the line in reaction to problems, to provide signal transitions and allow recovery of synchronization and framing.
All OSPF DR Routers The multicast IP address 224.0.0.6, listened for by DR and BDR routers.
All OSPF Routers The multicast IP address 224.0.0.5, listened for by all OSPF routers.
Alternate Mark Inversion A serial-line encoding standard that sends alternating positive and negative 3-volt signals for binary 1, and no signal (0 V) for binary 0.
alternate mode One of the two modes of MDRR, in which the priority queue is serviced between each servicing of the non-priority queues.
Alternate state An 802.1w RSTP port state in which the port is not the Root Port but is available to become the root port if the current root port goes down.
AMI See Alternate Mark Inversion.
anycast An IPv6 address type that is used by a number of hosts in a network that are providing the same service. Hosts accessing the service are routed to the nearest host in an anycast environment based on routing protocol metrics.
AR See access rate.
area (OSPF) A contiguous group of data links that share the same OSPF area number.
Area Border Router An OSPF router that connects to the backbone area and to one or more non-backbone area.
ARP See Address Resolution Protocol.
AS number A number between 1 and 64,511 (public) and 64,512 and 65,535 (private) assigned to an AS for the purpose of identifying a specific BGP domain.
AS_PATH A BGP path attribute that lists ASNs through which the route has been advertised. The AS_PATH includes four types of segments: AS_SEQ, AS_SET, AS_CONFED_SEQ, and AS_CONFED_SET. Often, this term is used synonymously with AS_SEQ.
AS_PATH access list 849
AS_PATH access list A Cisco IOS configuration tool, using the ip as-path access-list command, that defines a list of statements that match the AS_PATH BGP path attribute using regular expressions.
AS_PATH length A calculation of the length of the AS_PATH PA, which includes 1 for each number in the AS_SEQ, 1 for an entire AS_SET segment, and possibly other considerations.
AS_PATH prepending This term has two BGP-related definitions. First, it is the normal process in which a router, before sending an Update to an eBGP peer, adds its local ASN to the beginning of the AS_PATH path attribute. Second, it is the routing policy of purposefully adding one or more ASNs to the beginning of a route’s AS_PATH path attribute, typically to lengthen the AS_PATH and make the route less desirable in the BGP decision process.
AS_SEQUENCE A type of AS_PATH segment consisting of an ordered list of ASNs through which the route has been advertised.
AS_SET A type of AS_PATH segment consisting of an unordered list of ASNs consolidated from component subnets of a summary BGP route.
ASBR Autonomous System Boundary Router. An OSPF router that redistributes routes from some other source into OSPF.
ASN See AS number.
Assert message Sent by a PIM-DM or PIM-SM router when it receives a multicast packet for a group on a LAN interface that is in the outgoing interface list for the group; includes the administrative distance of the unicast routing protocol used to learn the network of the source with its metric value.
association ID When a wireless station connects to an access point, the access point assigns an association ID (AID) to the station. Various protocols, such as power-save mode, make use of the association ID.
Assured Forwarding A set of DiffServ PHBs that defines 12 DSCP values, with four queuing classes and three drop probabilities within each queuing class.
ATOMIC_AGGREGATE A well-known discretionary BGP path attribute that flags a route as being a summary route.
AutoQos AutoQoS is a macro that creates and applies quality of service configurations based on Cisco best-practice recommendations.