A

accept

JUNOS software syntax command used in a routing policy or a firewall filter. It halts the logical processing of the policy or filter when a set of match conditions is met. The specific route is placed into the routing table or announced to a neighbor. An IP packet is forwarded to the next hop along the network path.

action

Within a routing policy or firewall filter, an action denotes a specific function to perform on a route or IP packet.

active route

Route chosen by a router from all routes in the routing table to reach a specific destination. Active routes are installed into the forwarding table.

add/drop multiplexer (ADM)

SONET functionality that allows lower-level signals to be dropped from a high-speed optical connection.

address match conditions

The use of an IP address as a match criterion in a routing policy or a firewall filter.

Address Resolution Protocol (ARP)

Protocol for mapping IP addresses to MAC addresses.

adjacency

Link-state network neighbor status that represents two neighbors who have exchanged their link-state database information with each other.

Adjacency-RIB-In

Logical software table that contains BGP routes received from a specific neighbor.

Adjacency-RIB-Out

Logical software table that contains BGP routes to be sent to a specific neighbor.

aggregation

Combination of groups of routes that share the same most significant bits into a single entry in the routing table.

Alternate Priority Queuing (APQ)

Dequeuing method that has a special queue, similar to SPQ, which is visited each time the scheduler moves from one low priority queue to another low priority queue. The packets in the special queue still have a predictable latency, although the upper limit of the delay is higher than that with SPQ. Since the other configured queues share the remaining service time, queue starvation is usually avoided. See also Strict Priority Queuing (SPQ).

American National Standards Institute (ANSI)

The United States’ representative to the ISO. See also International Organization for Standardization (ISO).

application-specific integrated circuit (ASIC)

Specialized processors that perform specific functions on the router.

area

Routing subdomain that maintains detailed routing information about its own internal composition and that maintains routing information that allows it to reach other routing subdomains. In IS-IS, an area corresponds to a Level 1 subdomain. In IS-IS and OSPF, an area is a set of contiguous networks and hosts within an Autonomous System that have been administratively grouped together.

area border router

Router that belongs to more than one area. Used in OSPF. See also Open Shortest Path First (OSPF).

ASBR Summary LSA

OSPF link-state advertisement sent by an ABR to advertise the router ID of an ASBR across an area boundary. See also Autonomous System boundary router.

AS external-link advertisements

OSPF link-state advertisement sent by AS boundary routers to describe external routes that they know. These link-state advertisements are flooded throughout the AS (except for stub areas).

AS path

In BGP, the path to a destination. The path consists of the AS numbers of all domains a packet must go through to reach a destination.

Asynchronous Transfer Mode (ATM)

A high-speed multiplexing and switching method utilizing fixed-length cells of 53 octets to support multiple types of traffic.

ATM adaptation layer (AAL)

A series of protocols enabling various types of traffic, including voice, data, image, and video, to run over an ATM network.

ATM Line Interface (ALI)

Interface between ATM and 3G systems. See also Asynchronous Transfer Mode (ATM).

atomic

Smallest possible operation. An atomic operation is performed either entirely or not at all. For example, if machine failure prevents a transaction from completing, the system is rolled back to the start of the transaction, with no changes taking place.

attempt

OSPF adjacency state seen in a Non-Broadcast Multi-Access (NBMA) network that means the local router is to send a unicast hello packet to a neighbor for which it has not yet received any protocol packets.

authentication center (AUC)

Part of the Home Location Register (HLR) in 3G systems, the AUC performs computations to verify and authenticate the user of mobile phones.

Authentication Header (AH)

component of the IPSec protocol used to verify that the contents of a packet have not been changed, and to validate the identity of the sender. The actual packet data is not protected. See also encapsulating security payload (ESP).

Automatic Protection Switching (APS)

echnology used by SONET ADMs to protect against circuit faults between the ADM and a router and to protect against failing routers. See also add/drop multiplexer (ADM).

Autonomous System (AS)

set of routers under a single technical administration. Each AS normally uses a single Interior Gateway Protocol (IGP) and metrics to propagate routing information within the set of routers. Also called routing domain.

Autonomous System boundary router

In OSPF, routers that import routing information external to the protocol into the link-state database.

Autonomous System external-link advertisements

OSPF link-state advertisement sent by Autonomous System boundary routers to describe external routes that they know. These link- state advertisements are flooded throughout the Autonomous System (except for stub areas).

Autonomous System path

In BGP, the path to a destination. The path consists of the Autonomous System numbers of all the domains a packet must pass through to reach a destination.

auto-RP

One of three methods of electing and announcing the rendezvous point to group address mapping in a multicast network. A vendor-proprietary specification supported by the JUNOS software.