JNCIA-DC key terms

A two-tier data center topology where every leaf switch connects to every spine switch, giving consistent low latency and predictable east-west traffic paths between servers.

The access-tier switch in a spine-leaf fabric that connects servers and storage to the spine layer and typically acts as the Layer 3 gateway for attached hosts.

The aggregation-tier switch in a spine-leaf fabric that provides high-speed transit between leaf switches and does not normally connect to servers directly.

The physical IP-routed fabric that carries encapsulated overlay traffic, responsible only for delivering packets between tunnel endpoints using standard routing protocols.

A logical network built on top of the underlay that provides Layer 2 or Layer 3 connectivity between virtual endpoints regardless of their physical location.

A tunneling protocol that encapsulates Layer 2 frames inside UDP packets, extending Layer 2 segments across a Layer 3 fabric using 24-bit segment identifiers.

A 24-bit VXLAN Network Identifier that labels an overlay segment, allowing up to roughly 16 million isolated Layer 2 domains across a shared fabric.

A VXLAN Tunnel Endpoint that encapsulates and decapsulates VXLAN traffic, mapping local VLANs to VNIs and sourcing the outer IP header.

A BGP address family used to distribute MAC and IP reachability information for overlay endpoints, enabling control-plane learning instead of data-plane flooding.

An EVPN route that advertises a MAC address, optionally with an associated IP address, so remote VTEPs learn endpoint location without flooding.

A Layer 2 broadcast domain in Junos EVPN-VXLAN configurations that maps a VLAN to a VNI and defines the flooding and learning behavior for that segment.

Multichassis Link Aggregation, where two switches present a single LAG to a server or downstream device, providing link redundancy without spanning tree blocking.

Inter-Chassis Link, the dedicated link between two MC-LAG peers used to synchronize control-plane state and forward traffic between chassis when needed.

A bundle of physical links treated as one logical interface, increasing bandwidth and providing resilience if a member link fails.

Link Aggregation Control Protocol, an IEEE standard that negotiates and monitors member links of an aggregated bundle between two directly connected devices.

Juniper's network operating system, which separates configuration from operational state and applies committed changes atomically across the device.

A working copy of the device configuration that administrators edit without affecting running behavior until they issue a commit command.

The command that validates the candidate configuration and, if it passes checks, activates it as the running configuration on the device.

A validation-only command that parses and verifies the candidate configuration for syntax and semantic errors without making it active.

A command that restores a previously committed configuration, referenced by number, allowing rapid recovery from a bad change.

The Junos CLI mode entered with the configure command, where set, delete, and show commands modify the candidate configuration rather than display operational state.

The default Junos CLI mode for monitoring and troubleshooting, where commands such as show interfaces display live state and cannot change configuration.

A configuration-mode command that creates or modifies a single hierarchy element in the candidate configuration, commonly used in scripts and automation.

A configuration-mode command that removes a specified statement or hierarchy level from the candidate configuration when the change is committed.

A saved known-good configuration that can be activated with one command to restore service quickly after an unintended change.

Junos interface names in the form type-fpc/pic/port, such as ge-0/0/0 or xe-1/0/3, identifying physical and logical attachment points.

A logical sub-interface configured under a physical interface, carrying its own VLAN ID, addresses, and protocol family settings.

A Layer 2 broadcast domain isolated by a tag on trunk links, allowing multiple logical networks to share the same physical switching infrastructure.

A switch interface that carries traffic for multiple VLANs using 802.1Q tags, typically connecting switches or hypervisors rather than end-user devices.

A switch interface assigned to a single VLAN that sends and receives untagged frames, usually connecting to a server or endpoint device.

An operational-mode command that displays link state, speed, counters, errors, and configured addresses for one or all interfaces.

A manually configured route in the routing table that directs traffic to a next hop or discard action without running a routing protocol.

A route matching 0.0.0.0/0 that provides a next hop for any destination not covered by a more specific prefix in the routing table.

A next-hop address that resolves to a usable route in the routing table, allowing the associated static route to be installed and used.

The database of known destinations, next hops, preferences, and metrics that the router uses to select forwarding paths for packets.

A Junos value that ranks routes from different sources, where a lower number is preferred when multiple protocols offer the same prefix.

An operational-mode command that displays routing table entries, including active and inactive routes, next hops, and preference values.

A stateless Junos access control list applied to an interface or forwarding path that matches packet fields and takes terminating or non-terminating actions.

A rule inside a firewall filter that contains match conditions and an action; terms are evaluated in order until one matches and terminates.

A traffic-control mechanism that measures packet or byte rates against configured limits and applies actions such as discard or marking to excess traffic.

A firewall filter applied to the loopback interface that protects the routing engine by restricting which traffic can reach device control-plane services.

A Junos policy statement that matches routes on criteria such as prefix or community and applies actions like accept, reject, or metric modification.

A named block within routing policy containing match conditions and actions, evaluated top to bottom until a terminating action is reached.

A routing policy applied to routes received from a protocol before they are installed in the routing table, commonly used to filter or modify learned routes.

A routing policy applied to routes advertised from the routing table into a protocol, controlling which prefixes are sent to neighbors.

A BGP attribute carrying a tag value that routing policy can match on to influence route filtering, preference, or advertisement decisions.

A forwarding behavior that installs multiple next hops of equal preference for the same prefix, spreading traffic across parallel paths in a fabric.

A BGP router that receives routes from clients and reflects them to other clients, removing the need for a full mesh of iBGP sessions.