JNCIP-SP flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

IS-IS ATT bit

Set by a Level 1/Level 2 router in its L1 LSP to tell L1-only routers that a default route toward the L2 backbone is available through it.

BGP local preference

A well-known discretionary attribute used inside an AS. Higher values are preferred, and it is evaluated before AS path length in the Junos path-selection algorithm.

BGP MED

Multi-Exit Discriminator, an optional non-transitive attribute that hints to a neighboring AS which entry point to prefer. Lower values are preferred, and it is compared after AS path.

Route reflector cluster ID

A 32-bit identifier configured on a route reflector. All reflectors in one cluster must share it so that reflected routes can be recognized and loops avoided.

Next-hop self

A BGP export policy action that rewrites the next hop of advertised routes to the local router address, ensuring iBGP peers can resolve the next hop via IGP.

LDP FEC

Forwarding Equivalence Class. LDP binds a label to each IGP prefix, and packets destined for that prefix are forwarded using the assigned label along the label-switched path.

RSVP-TE PATH message

Sent downstream by the ingress LSR to request a label-switched path with explicit route and bandwidth requirements; the receiver replies with a RESV message reserving resources.

Penultimate hop popping

The second-to-last router in an LSP removes the outer label before forwarding to the egress router, so the egress receives an unlabeled packet and avoids a double lookup.

Segment routing prefix-SID

An IGP-advertised identifier (index or absolute value) that maps to an MPLS label for a prefix. Packets are steered by stacking SIDs in the header.

TI-LFA

Topology-Independent Loop-Free Alternate. A segment-routing-based fast-reroute mechanism that precomputes a backup path using a repair list of SIDs, protecting against link and node failures.

Route target

A BGP extended community attached to VPN routes. A VRF imports a route only if the route's target matches one of the VRF's configured import targets.

Route distinguisher

An 8-byte value prepended to a VPN prefix to make it unique across VRFs. It does not control import or export; that is the role of route targets.

BGP no-export community

Well-known community 0xFFFFFF01. Routes carrying it are advertised to other peers within the local AS but are not sent to external eBGP peers.

BGP large community

A 12-byte attribute holding three 32-bit values, typically global-admin:local-data1:local-data2. It is useful for tagging routes in networks that use 4-byte AS numbers.

Junos commit confirmed

A commit option that activates the configuration temporarily and automatically rolls back after the specified number of minutes unless a confirming commit is issued.

Junos rollback 1

A configuration-mode command that loads the previous committed configuration into the candidate, allowing comparison or re-commit after an unintended change.

show route hidden

A Junos command that lists routes rejected by import policy or otherwise inactive, which is useful when a route is missing from the active table.

PIM-SM shared tree

A distribution tree rooted at the rendezvous point. Receivers join via (*,G) joins, and the last-hop router may switch to a source-specific shortest-path tree.

RPF check

Reverse Path Forwarding. A multicast packet is accepted only if it arrives on the interface that the unicast routing table uses to reach the source.

BFD

Bidirectional Forwarding Detection. A lightweight protocol that detects path failures in milliseconds and notifies routing protocols such as BGP, OSPF, and IS-IS.

OSPF network type p2p

A point-to-point interface type that skips DR/BDR election and forms a direct adjacency, commonly used on unnumbered core links between service provider routers.

BGP additional paths

A capability that allows advertisement of multiple paths for the same prefix, improving convergence and multipath utilization by avoiding a single best-path advertisement.

LDP session establishment

LDP peers discover each other via UDP port 646, then establish a TCP session on port 646 to exchange label mappings. A reachable loopback is normally required.

MPLS label stack

An ordered set of labels pushed onto a packet. The outermost label is swapped at each LSR, and the bottom label identifies the forwarding equivalence class.

BGP origin attribute

A well-known mandatory attribute indicating how the route was learned: IGP (i), EGP (e), or Incomplete (?). IGP is preferred over EGP, which is preferred over Incomplete.

BGP AS path prepending

An export policy action that repeats the local AS number in the AS path to make the path longer and less preferred for inbound traffic from remote ASes.

SRv6 SID

A 128-bit IPv6 address that encodes a segment instruction. A segment list in the SRH steers the packet through an ordered set of these SIDs.

VRF import policy

The set of route targets configured on a VRF. Routes whose extended community matches an import target are installed into that VRF's routing table.

Junos export policy

Policy applied to routes before they are advertised to a BGP peer. If no term accepts the route, the default action rejects it from advertisement.

show bgp summary

A Junos command that displays each peer's state, received and advertised prefix counts, and uptime, which is useful for confirming session establishment quickly.

PIM rendezvous point

The router that roots the shared distribution tree in PIM-SM. Sources register with it, and receivers join the (*,G) tree toward it before switching to the source tree.

MPLS explicit null label

Label value 0 (IPv4) or 2 (IPv6) that the egress router advertises to keep the EXP bits meaningful, preventing the penultimate hop from popping the label.