Cisco ENARSI 300-410 key terms

A ranking from 0 to 255 that a router uses to choose between routes to the same prefix learned from different sources; lower values are preferred, and 255 means the route is never installed.

A static route configured with a higher administrative distance than the primary route so it stays out of the routing table until the preferred path fails, providing simple backup connectivity.

A mechanism that pairs a static route with an object tracking probe such as ICMP echo; if the probe fails, the tracked object goes down and the router withdraws the associated route.

A method of forwarding packets based on route maps that match criteria such as source address, protocol, or packet length instead of the destination-based routing table lookup.

Virtual Routing and Forwarding without MPLS; a router keeps multiple independent routing and forwarding tables on one device, separating customer or tenant traffic on shared physical links.

An ordered list of match and set clauses used to filter or modify routing information and to steer policy; clauses are evaluated top-down and the first match wins unless continue is configured.

A filter applied to routing updates entering or leaving an interface or a routing process, permitting or denying prefixes by access list or prefix list before they enter the routing table.

A stateless, efficient filter that matches network prefixes and prefix lengths using sequence numbers, commonly used to control route advertisements and redistribution instead of access lists.

The process of injecting routes learned by one routing protocol into another, requiring seed metrics, metric translation, and filtering to prevent loops and suboptimal path selection.

The initial metric assigned to redistributed routes because the receiving protocol cannot interpret the source protocol's metric; without it, routes are often rejected or set to infinity.

A logical grouping of OSPF interfaces that limits link-state flooding and requires all areas to connect to the backbone area 0 through an ABR or a virtual link.

Link-state advertisement categories that carry topology and prefix data; key types include router (1), network (2), summary (3), ASBR summary (4), external (5), and NSSA external (7).

An area that blocks type 5 external LSAs and relies on a default route from the ABR; totally stubby areas additionally block type 3 summaries, and NSSA areas allow limited external injection.

A logical point-to-point adjacency carried through a transit area that connects a discontiguous area to the backbone or joins two parts of area 0 across another area.

The relationship OSPF routers form after matching hello parameters and completing database exchange; mismatched area, timers, authentication, MTU, or network type prevents the FULL state.

The lowest end-to-end metric recorded for a destination since the route last became active; a neighbor's reported distance must be lower to qualify as a feasible successor.

The rule that a neighbor's reported distance must be less than the local feasible distance for that neighbor to become a feasible successor, guaranteeing a loop-free backup path.

How far a query travels when a route is lost and no feasible successor exists; stub routing and summarization limit the scope so unaffected routers are not forced into active state.

A configuration that advertises a router as a stub so it receives only a subset of queries, reducing query propagation toward edge devices that should not transit traffic.

The ordered tie-breaking process for identical prefixes, considering weight, local preference, locally originated routes, AS path length, origin, MED, eBGP over iBGP, and IGP metric.

A well-known discretionary attribute shared within an autonomous system that ranks preferred exit points; higher values win, and it is typically set inbound on eBGP sessions.

Multi-Exit Discriminator, an optional non-transitive attribute that hints to a neighboring AS which entry point is preferred; lower values are better and comparison is limited by default.

The sequence of autonomous system numbers a prefix traversed, used for loop prevention and path selection; shorter paths are preferred, and prepending artificially lengthens a path.

An iBGP router allowed to reflect routes learned from one iBGP peer to others, removing the full-mesh requirement; cluster lists and originator IDs prevent reflection loops.

A technique that splits a large autonomous system into sub-AS internal groups with special confederation peering, reducing iBGP session counts while presenting one AS externally.

A service where provider edge routers exchange customer routes as VPNv4 prefixes over MP-BGP and forward traffic using label stacks, keeping customer routing separate across the provider core.

An eight-byte value prepended to a customer IPv4 prefix to make it unique in VPNv4 BGP, allowing overlapping address space from different customers to coexist.

A BGP extended community attached to VPN routes that controls import and export between VRFs, determining which customer sites can learn which prefixes.

Dynamic Multipoint VPN builds hub-and-spoke and spoke-to-spoke IPsec tunnels on demand using mGRE, NHRP, and a routing protocol, without static tunnel configuration per spoke.

Next Hop Resolution Protocol lets spokes register their public addresses with the hub and query for other spokes' addresses, enabling direct dynamic tunnels in DMVPN phase 2 and 3.

Generic Routing Encapsulation wraps passenger protocols inside IP for transport across an IP network; it supports multicast and routing protocols but offers no encryption on its own.

A configuration that binds an IPsec profile to a tunnel interface so traffic entering the tunnel is encrypted automatically, commonly used with GRE or mGRE for scalable VPNs.

An IKEv2-based VPN framework on Cisco IOS that unifies site-to-site, remote-access, and hub-spoke designs using tunnel interfaces, profiles, and authorization attributes.

A policy that rate-limits or drops traffic destined to the router's own control plane, protecting CPU and routing protocols from floods and reconnaissance without affecting transit traffic.

Control Plane Policing, implemented with a service policy applied globally that classifies punted traffic and enforces rate limits per class, often tuned to protect routing and management protocols.

Unicast Reverse Path Forwarding checks that a packet's source address is reachable through the interface it arrived on; strict mode drops spoofed sources, while loose mode only checks reachability.

The framework that verifies user identity using local or remote methods such as TACACS+ and RADIUS, with fallback ordering defined by method lists on lines and services.

TACACS+ is Cisco-proprietary, encrypts the full payload, uses TCP 49, and separates authentication, authorization, and accounting; RADIUS is standards-based, encrypts only passwords, and uses UDP.

A Layer 2 security feature that classifies switch ports as trusted or untrusted and drops DHCP offers from untrusted ports, preventing rogue servers and building a binding table for inspection.

A feature that validates ARP packets against the DHCP snooping binding table, discarding replies with mismatched MAC or IP pairs to stop ARP spoofing and man-in-the-middle attacks.

A filter that permits only source IP addresses found in the DHCP snooping binding table, optionally with matching MAC, on untrusted ports to block address spoofing.

Hot Standby Router Protocol is a Cisco first-hop redundancy protocol where an active and standby router share a virtual IP and MAC, with preemption and tracking controlling failover.

Virtual Router Redundancy Protocol is a standards-based first-hop redundancy protocol similar to HSRP, using a master and backups with a virtual router that owns a shared address.

The practice of tying HSRP or VRRP priority to an object such as an uplink interface or IP SLA probe so the gateway role moves when the preferred path fails.

A network management protocol that uses SSH transport, XML-encoded data, and YANG models to read and edit configuration datastores, supporting candidate configs and confirmed commits.

A lightweight HTTP-based protocol that exposes YANG-modeled data using REST methods such as GET, POST, PATCH, and DELETE, typically over HTTPS with JSON or XML encoding.

A hierarchical data modeling language that defines configuration and state for network devices, providing the schema that NETCONF, RESTCONF, and gNMI carry and validate.

gRPC Network Management Interface streams telemetry and supports get, set, and subscribe operations against YANG-modeled data, commonly used for high-frequency streaming telemetry.

Embedded Event Manager applet is a scripted policy triggered by events such as syslog patterns, timers, or interface changes, running actions like CLI commands or email alerts.

An Embedded Event Manager policy written in Python that reacts to events and calls Cisco object-oriented APIs to inspect or change device state programmatically.