JNCIP-SP key terms

An interior gateway protocol area that holds a flat link-state database and routes only within its own area; it forwards traffic destined outside the area toward a Level 1/Level 2 router.

The IS-IS backbone level that carries inter-area reachability; its database spans all Level 2 routers in the domain and forms the path between areas.

A router attached to both IS-IS levels, maintaining separate Level 1 and Level 2 databases and advertising itself into Level 1 with the attached bit set.

A flag in the IS-IS Level 1 link-state PDU that tells Level 1 routers the originator has Level 2 connectivity, so they install a default route toward it.

The practice of redistributing selected Level 2 or external prefixes into IS-IS Level 1 so intra-area routers can reach them without a default route, typically controlled with policy.

Type-Length-Value encoding used by IS-IS and other protocols to carry optional or extended information inside a PDU, allowing new capabilities without changing the base packet format.

The 32-bit IS-IS metric encoding carried in extended reachability TLVs, replacing the 6-bit narrow metric and enabling traffic engineering and segment routing metric values.

A logical grouping of OSPF interfaces that shares one link-state database; all routers in an area have identical topology information, and inter-area traffic passes through the backbone area 0.

The record formats OSPF uses to describe routers, networks, summaries, and externals; types 1 through 5 cover intra-area, summary, and external information, while types 7 and 9-11 extend them.

An OSPF area that blocks external LSAs and reaches external destinations through a default route injected by its area border router, reducing database and CPU load.

A Cisco-defined OSPF area that blocks both external LSAs and inter-area summary LSAs, relying solely on a default route from the ABR for all destinations outside the area.

An OSPF area that blocks type 5 externals but permits type 7 LSAs originated inside it; the area border router translates type 7 into type 5 at the backbone.

Fields attached to BGP updates that describe reachability and influence best-path selection, such as AS path, next hop, local preference, MED, and communities.

The ordered comparison BGP runs over candidate routes, weighing attributes such as weight, local preference, AS path length, origin, MED, and router ID before choosing one path.

A well-known discretionary BGP attribute shared among iBGP peers that ranks preferred exit points; the higher value wins and it is not advertised to external peers by default.

An optional non-transitive BGP attribute sent to external peers to signal preferred entry points into an AS; lower values are preferred and comparison is typically limited to the same neighboring AS.

A technique of repeating the local AS number in the AS path to make a route appear longer and therefore less attractive to inbound BGP selection.

An iBGP router allowed to reflect routes learned from one client to other clients and non-clients, removing the need for a full iBGP mesh within an AS.

A group of route reflectors sharing a cluster ID so that reflected routes are recognized and loops are prevented when multiple reflectors serve the same clients.

A BGP attribute added by a route reflector to record the original router ID of a reflected route, preventing the originating router from accepting its own route back.

A method of dividing one autonomous system into sub-ASes that run iBGP internally while presenting a single AS number to external peers, reducing full-mesh requirements.

The mechanisms that stop routing loops, chiefly rejecting updates whose AS path already contains the local AS, plus originator ID and cluster list checks inside an AS.

The non-Turing-complete configuration language used to write policies that match routes on attributes and take actions such as accept, reject, or attribute modification.

A named policy block containing ordered terms, each with match conditions and actions, evaluated top-down until a route matches and a terminating action applies.

A named list of IP prefixes with optional length ranges used inside routing policy to match or filter routes by destination and mask length.

A pattern syntax using AS numbers and operators such as anchors, wildcards, and repetition to match AS paths in policy for filtering or attribute setting.

An ordered set of short labels pushed onto a packet; each label identifies a forwarding entry, and routers swap or pop labels as the packet crosses the MPLS domain.

The unidirectional tunnel formed by a sequence of label bindings along a path through an MPLS network, along which packets are forwarded by label rather than by IP lookup.

A protocol that distributes label bindings between neighboring routers based on the IGP best path, building label switched paths without explicit traffic engineering constraints.

A signaling protocol that establishes explicitly routed label switched paths with bandwidth reservations and constraints, supporting fast reroute and traffic engineering tunnels.

The behavior where the second-to-last router in a label switched path pops the top label so the egress router receives a plain IP packet and avoids a double lookup.

A source-routing architecture where the ingress node encodes a list of segments, such as node SIDs or adjacency SIDs, in the packet header to steer traffic without per-path state in the core.

The Segment Routing Global Block, a reserved range of MPLS labels from which globally significant prefix SIDs are allocated; all nodes must agree on the range for consistent forwarding.

A prefix segment that identifies a router by its loopback address, allowing traffic to be steered to that node along the shortest path computed by the IGP.

A local segment that identifies a specific link or adjacency on a router, used to steer traffic over a chosen next hop independent of the shortest-path tree.

An index advertised in the IGP for a prefix that maps to a label within the SRGB, letting other routers forward to that prefix using the globally significant segment.

A service that transports customer Layer 2 frames, such as Ethernet or Frame Relay, across a provider network by encapsulating them and forwarding based on attachment circuits.

A multipoint Layer 2 VPN service that emulates a bridged LAN across the provider network, learning MAC addresses and flooding unknown, broadcast, and multicast frames to all sites.

An emulated point-to-point circuit that carries customer Layer 2 frames across a packet-switched network between two provider edge devices using a standardized encapsulation.

A BGP-based control plane for Layer 2 and Layer 3 VPN services that distributes MAC and IP reachability, enabling multipoint Ethernet with control-plane learning and multihoming.

The customer-facing interface or VLAN on a provider edge router that connects a customer site to a Layer 2 VPN service instance.