JNCIE-SP key terms

A Junos commit option that activates configuration changes temporarily and automatically rolls them back unless a second commit is issued within a set time, protecting against losing management access during risky changes.

A saved known-good configuration on a Junos device that can be restored with a single command, used to recover quickly after a failed change or device misconfiguration.

A Junos operational command that reverts the candidate configuration to a previously committed version, identified by a numbered history index, allowing rapid recovery from configuration errors.

Junos feature that applies shared configuration statements to multiple sections through inheritance, reducing duplication and enabling per-interface or per-protocol overrides of common settings.

A Junos statement that inserts a named configuration group's contents at a specific point in the hierarchy, with the local configuration taking precedence over inherited values.

Junos in-service software upgrade capability that keeps forwarding and routing active during a software upgrade, typically requiring redundant Routing Engines and supported protocols with graceful restart.

Graceful Routing Engine Switchover, a Junos high availability feature that preserves forwarding state and kernel state during a Routing Engine failover so traffic continues while the new engine takes over.

Nonstop active routing, a Junos feature that synchronizes routing protocol state between Routing Engines so that a switchover does not reset protocol adjacencies or require neighbor reconvergence.

A protocol mechanism where a restarting router signals neighbors to retain forwarding state and adjacencies for a defined period, avoiding traffic loss during control-plane restart.

Bidirectional Forwarding Detection, a lightweight hello protocol that rapidly detects path failures between two endpoints and can trigger faster convergence for routing protocols and static routes.

A logical grouping of OSPF interfaces that confines topology information and link-state flooding, with all areas connected to the backbone area 0 through area border routers.

Area Border Router, an OSPF or IS-IS router attached to multiple areas that summarizes or filters prefix information between them and originates summary advertisements into the backbone.

A hierarchy in IS-IS where Level 1 routers share a single area and Level 2 routers form the backbone; Level 1-2 routers leak or advertise prefixes between the two levels.

Aggregating multiple more-specific prefixes into a single less-specific advertisement, reducing routing table size and hiding topology changes but potentially causing suboptimal forwarding.

An ordered set of Junos policy terms that match routes on prefixes, communities, or attributes and apply actions such as accept, reject, or attribute modification.

A Junos policy construct that matches on prefix lists or route attributes to permit or deny routes, commonly applied to control redistribution or BGP advertisements.

Injecting routes learned from one routing protocol into another, requiring policy to control which prefixes are imported and to set metrics or attributes for proper preference.

A numeric preference assigned to each route source that determines which route is installed when multiple protocols offer the same prefix; lower values are preferred.

A well-known discretionary attribute distributed within an autonomous system that ranks preferred exit points; higher values are preferred and it is set on inbound eBGP policy.

Multi-Exit Discriminator, an optional non-transitive BGP attribute that suggests a preferred entry point into an autonomous system; lower values are preferred and it is typically compared only between paths from the same neighbor AS.

A BGP attribute listing the autonomous systems a route has traversed; it is used for loop prevention and path selection, with shorter paths generally preferred.

An iBGP router allowed to reflect routes to other iBGP clients, removing the need for a full mesh; it uses cluster IDs and originator IDs to prevent loops.

The requirement that every iBGP router peer with every other within an AS, since iBGP-learned routes are not re-advertised to other iBGP peers by default.

A method of dividing a large autonomous system into sub-ASes that peer internally with confederation-specific rules, reducing iBGP mesh size while appearing as one AS externally.

A mechanism that penalizes repeatedly flapping prefixes, suppressing advertisement of unstable routes for a period to protect network stability, configurable with penalties and thresholds.

Label Distribution Protocol, which establishes label-switched paths by mapping FEC prefixes to labels and distributing those bindings between adjacent MPLS routers.

A traffic engineering signaling protocol that reserves bandwidth along an explicit or constrained path and distributes labels, enabling MPLS LSPs with bandwidth guarantees and fast reroute.

An ordered set of MPLS labels pushed onto a packet, where the outermost label directs the next hop and inner labels identify VPNs or other services.

Penultimate Hop Popping, where the router before the egress removes the outer label so the egress receives an unlabeled or single-labeled packet, reducing lookup work.

Virtual Routing and Forwarding, a per-customer routing table instance on a provider edge router that isolates customer routes and is bound to interfaces and a route distinguisher.

An identifier prepended to customer prefixes to make them unique in MP-BGP, allowing overlapping address space between VPNs on the same provider network.

A BGP extended community attached to VPN routes that controls which VRFs import or export those routes, forming the basis of VPN membership and route leaking.

Multiprotocol BGP, an extension carrying address families beyond IPv4 unicast, such as VPN-IPv4, IPv6, and EVPN, using additional path attributes for each family.

An inter-AS VPN approach where autonomous system border routers exchange labeled VPN-IPv4 routes over eBGP, keeping customer VRFs only on provider edge routers.

A VPN model where a service provider transports another provider's labeled routes without participating in the customer VPN, using labeled eBGP or IGP plus LDP between them.

Virtual Private LAN Service, an MPLS layer 2 service that emulates a multipoint Ethernet LAN across the provider network, learning MAC addresses per VPLS instance.

Ethernet VPN, a BGP-based control plane for layer 2 and layer 3 services that distributes MAC and IP reachability using route types, supporting MPLS and VXLAN encapsulation.

The EVPN procedure for moving a MAC address between provider edge nodes, using sequence numbers in MAC advertisement routes to resolve duplicate ownership during host relocation.

Connecting a customer site to multiple provider edge routers for redundancy; in EVPN, Ethernet segment identifiers and designated forwarders prevent duplicate flooding and loops.

Protocol Independent Multicast Sparse Mode, which builds shared and shortest-path trees using rendezvous points and explicit joins, suitable for sparsely distributed receivers.

Rendezvous Point, the shared root of the PIM-SM shared tree where sources register and receivers join before switching to a shortest-path tree.

Source-Specific Multicast, where receivers join a channel identified by source and group address, eliminating the rendezvous point and shared tree for simpler, more secure delivery.

Multicast Source Discovery Protocol, which shares active source information between rendezvous points in different PIM-SM domains so receivers can join sources across domains.

Multicast Label Distribution Protocol, which builds point-to-multipoint and multipoint-to-multipoint label-switched paths for multicast transport over MPLS without requiring PIM in the core.

Internet Group Management Protocol, used by hosts and routers on a local segment to signal group membership so that multicast traffic is forwarded only where receivers exist.

A Junos stateless filter applied to interfaces or forwarding paths that matches packet fields and applies actions such as accept, discard, count, or police.

Junos traffic treatment that classifies packets, assigns forwarding classes and loss priorities, and schedules transmission with shaping, queuing, and drop profiles.

A rate-limiting mechanism that measures traffic against configured bandwidth and burst sizes and applies actions such as discard or marking to excess packets.