Route chosen from all routes in the routing table to reach a destination. Active routes are installed into the forwarding table.
add/drop multiplexer
See [ADM]
Address Resolution Protocol
See [ARP]
adjacency
Portion of the local routing information that pertains to the reachability of a single neighbor over a single circuit or interface.
ADM
Add/drop multiplexer. SONET functionality that allows lower-level signals to be dropped from a high-speed optical connection.
aggregation
Combination of groups of routes that have common addresses into a single entry in the routing table.
ANSI
American National Standards Institute. The United States' representative to the ISO.
APS
Automatic Protection Switching. Technology used by SONET ADMs to protect against circuit faults between the ADM and a router and to protect against failing routers.
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, 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.
ARP
Address Resolution Protocol. Protocol for mapping IP addresses to MAC addresses.
AS
Autonomous system. 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.
AS boundary router
In OSPF, routers that exchange routing information with routers in other ASs.
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 route to a destination. The path consists of the AS numbers of all routers a packet must go through to reach a destination.
ASIC
Application-specific integrated circuit. Specialized processors that perform specific functions on the router.
ATM
Asynchronous Transfer Mode. A high-speed multiplexing and switching method utilizing fixed-length cells of 53 octets to support multiple types of traffic.
Automatic Protection Switching
See [APS]
autonomous system
See [AS]
autonomous system boundary router
In OSPF, routers that exchange routing information with routers in other ASs.
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 route to a destination. The path consists of the autonomous system numbers of all the routers a packet must pass through to reach a destination.