JNCIP-ENT key terms

A two-tier hierarchy in IS-IS where Level 1 routers stay inside one area and Level 2 routers form the backbone that connects areas. Level 1-2 routers sit on both, leaking a default or selected prefixes between them.

A neighbor relationship formed after routers exchange and acknowledge hello PDUs with matching level, area, and authentication settings. Junos shows it as Up in the IS-IS neighbor table and requires matching MTU and broadcast or point-to-point media type.

A logical grouping of OSPF interfaces that confines topology and link-state flooding. Area 0 is the backbone, and every other area must attach to it through an Area Border Router, which summarizes routes between areas.

The category of link-state advertisement flooded by OSPF. Router (Type 1) and network (Type 2) LSAs stay inside an area, while summary (Type 3), ASBR summary (Type 4), and external (Type 5) LSAs cross area or domain boundaries.

An OSPF area configured to block Type 5 external LSAs, replacing them with a default route from the ABR. Totally stubby areas additionally suppress Type 3 summaries, leaving only intra-area routes and one default.

An interface whose connected subnet is advertised into a routing protocol without sending or processing hellos on it. Used on user-facing or loopback links so the prefix is reachable while adjacencies stay off that segment.

A BGP speaker allowed to reflect routes learned from one iBGP peer to other iBGP peers, removing the need for a full mesh. It adds an originator ID and cluster list to prevent loops.

A group of route reflectors and their clients identified by a cluster ID. The cluster list attribute records clusters a route has traversed, and a router discards a route whose list already contains its own cluster ID.

The ordered tie-breaking process for choosing one best route among candidates, starting with highest local preference, then shortest AS path, then lowest origin, MED, and so on. Junos lets you influence order with path-selection configuration.

A well-known discretionary attribute spread through iBGP that signals preferred exit points. Higher values win, and it is typically set on inbound eBGP routes so all routers in an AS agree on the exit path.

The Multi-Exit Discriminator attribute that hints to a neighboring AS which of several entry links is preferred. Lower is better, and it is compared only between paths from the same neighboring AS by default.

The address a router uses to reach the destination advertised in a BGP update. On iBGP the next hop is usually unchanged, so the interior routing table must resolve it or the route is hidden as inaccessible.

Optional transitive tags attached to routes so policy can match groups of prefixes instead of individual ones. Standard communities are 32-bit values written as AS:number, and well-known values like no-export control propagation.

A multicast routing mode where traffic flows only after receivers join a group. A shared rendezvous point tree is built first, then routers may switch to a shortest-path tree toward the source.

The router that serves as the meeting place for sources and receivers in PIM sparse mode. Sources register with it and receivers join the shared tree rooted there, identified by a static or dynamic method such as anycast RP.

The periodic message a downstream router sends upstream toward a source or rendezvous point to request or stop a multicast flow. Joins refresh before timeout, and prunes remove unneeded branches from the distribution tree.

A unicast encapsulation a first-hop router uses to send multicast packets to the rendezvous point before a native tree exists. The RP decapsulates them and may reply with a register-stop once the tree is built.

A multicast forwarding rule that accepts a packet only if it arrived on the interface the unicast route back to the source points to. A failure usually signals a routing or topology mismatch.

A switch feature that listens to host IGMP reports and leaves to track which ports want which groups. It forwards multicast only to interested ports instead of flooding every port in the VLAN.

The function a port takes in Rapid Spanning Tree: root, designated, alternate, or backup. Roles are negotiated quickly through proposal and agreement, replacing the slower timer-based convergence of classic STP.

A port configured to connect to an end host, so it moves straight to forwarding and does not expect BPDUs. Receiving a BPDU on it causes the port to lose edge status and rejoin the spanning tree.

The frame switches exchange to elect a root bridge and agree on topology. Configuration BPDUs carry bridge and port identifiers and timers, while topology change notifications speed up MAC table aging.

The process of choosing the switch with the lowest bridge ID, a combination of priority and MAC address, as the tree's center. All other switches then select a least-cost root path and one root port each.

A protection feature that error-disables or blocks a port if it receives a BPDU, typically applied to host-facing edge ports. It prevents an unauthorized switch from joining and reshaping the spanning tree.

A feature that keeps a port in a blocking state if it receives superior BPDUs that would make a neighboring switch the root. It protects the intended root bridge location on designated ports facing other switches.

The client software or device that requests network access through an authenticator port. It responds to Extensible Authentication Protocol requests and supplies credentials until the authentication server accepts or rejects it.

The switch or access point port that controls access, relaying Extensible Authentication Protocol messages between supplicant and authentication server. Until authentication succeeds it typically permits only EAPOL traffic.

The Extensible Authentication Protocol over LAN frame format used between supplicant and authenticator. It carries EAP request, response, success, and failure messages, plus the start and logoff frames that begin and end a session.

A typed field in a RADIUS message that carries authentication or authorization data, such as the user name, tunnel parameters, or filter ID. Vendors extend the set to deliver dynamic VLAN or policy results to the switch.

A process where the authentication server returns a VLAN identifier in its accept message and the switch places the port in that VLAN. Access can change per session without reconfiguring the port.

An extension of Link Layer Discovery Protocol for voice endpoints that advertises network policy, VLAN, and QoS settings. Phones use it to learn the voice VLAN and priority automatically from the switch.

A separate VLAN carrying IP phone traffic so voice can be isolated, prioritized, and secured apart from data. Phones often tag voice frames while passing untagged data from an attached PC.

A mechanism that limits the number of concurrent calls or bandwidth on a link so existing calls keep acceptable quality. It can reject or reroute new calls when the configured threshold is reached.

The point in the network where a packet's class-of-service markings are accepted as valid. Markings from untrusted hosts are usually rewritten at the access edge, while trusted links preserve them.

A six-bit field in the IP header that labels a packet's per-hop behavior. Values map to classes such as expedited forwarding or assured forwarding, and routers use them to select queues and drop profiles.

A per-hop behavior, usually DSCP 46, giving low loss, low latency, and low jitter treatment for real-time traffic such as voice. It is served from a priority queue with a strict or shaped limit.

A per-hop behavior group with four classes and three drop precedences, so packets get a guaranteed share of bandwidth and are dropped selectively under congestion. Markings like AF41 designate class and drop priority.

The CoS component that maps incoming packets to forwarding classes and loss priorities, using fields such as DSCP, IP precedence, or interface. It runs before policing, queuing, and scheduling decisions.

The category of Ethernet VPN border gateway protocol advertisement. Type 2 carries MAC and IP reachability, Type 3 carries inclusive multicast, Type 4 carries Ethernet segment, and Type 5 carries IP prefixes.

A logical Ethernet VPN construct on a provider edge device that binds a VLAN or bridge domain to a route target and RD. It defines which MAC and IP routes are advertised and imported for that service.

The set of links on a customer site that connect to multiple provider edge devices and are treated as one logical attachment. A unique identifier and designated forwarder election prevent duplicate flooded frames.

The provider edge device elected per Ethernet segment to forward broadcast, unknown unicast, and multicast traffic toward the multihomed site. Other members stay standby to avoid duplicate delivery.