Cisco ENCOR: Enterprise Network Core Technologies: key terms

Flashcards for this exam Cisco ENCOR: Enterprise Network Core Technologies guide Class dates

• Adjacency TableThe CEF table holding Layer 2 rewrite information for each next hop, built from ARP and other resolution protocols.Advanced
• Administrative DistanceA Cisco value (0-255) ranking the trustworthiness of route sources; the lowest AD wins when protocols offer the same prefix.Foundational
• Allowed VLAN ListThe set of VLANs permitted to traverse a trunk, all VLANs (1-4094) by default on Cisco.Foundational
• Alternate PortAn RSTP port role for a discarding port that provides a backup path to the root bridge via another switch.Intermediate
• Application-Aware Routing (AAR)A Cisco SD-WAN data policy that steers applications over tunnels meeting SLA thresholds for loss, latency and jitter measured by BFD.Advanced
• Area Border Router (ABR)An OSPF router with interfaces in area 0 and at least one other area, which summarizes routes between them.Intermediate
• AS Path PrependingAdding extra copies of an ASN to the AS_PATH of advertised routes to make a path less attractive to other ASes.Intermediate
• AS_PATH AttributeA well-known mandatory BGP attribute listing the ASNs a route has traversed; used for loop prevention and path length comparison.Intermediate
• Assured Forwarding (AF)A DiffServ PHB group of four classes (AF1-AF4) each with three drop precedences (AFx1-AFx3).Intermediate
• Auto-RPCisco-proprietary method for distributing RP information using candidate RP announcements to 224.0.1.39 and mapping agent discovery to 224.0.1.40.Advanced
• Auto-SummaryAutomatic summarization of routes to classful network boundaries when advertised across a different major network.Intermediate
• Autonomous System (AS)A set of networks under one administrative control with a single routing policy, identified in BGP by an AS number.Foundational
• Autonomous System Boundary Router (ASBR)An OSPF router that redistributes external routes into OSPF, originating Type 5 or Type 7 LSAs.Intermediate
• Autonomous System Number (ASN)A number identifying a BGP autonomous system: 2-byte (1-65535) or 4-byte (up to 4,294,967,295).Intermediate
• AutoQoSCisco feature that automatically generates recommended QoS configuration for voice, video and data on switches and routers.Intermediate
• Backup Designated Router (BDR)The OSPF router that monitors the DR on a multi-access segment and takes over if the DR fails.Intermediate
• Best EffortThe default QoS model where all packets are treated equally with no guarantees, typically first in first out.Foundational
• BGP Aggregate AddressA BGP command that creates a summary route when at least one component exists in the BGP table.Intermediate
• BGP Best Path SelectionBGP's ordered decision process for choosing one best path per prefix.Intermediate
• BGP CommunityAn optional transitive 32-bit BGP attribute (often written AS:value) used to tag routes for policy decisions.Intermediate
• BGP Default-OriginateA BGP neighbor option that sends a default route to a specific peer, even if none exists in the BGP table.Intermediate
• BGP EVPNThe MP-BGP address family (L2VPN/EVPN, AFI 25/SAFI 70) that carries EVPN routes between VTEPs or PEs.Advanced
• BGP Full MeshThe requirement that every iBGP speaker peer with every other iBGP speaker unless route reflectors or confederations are used.Intermediate
• BGP Message TypesBGP's message types: OPEN, UPDATE, KEEPALIVE, NOTIFICATION and ROUTE-REFRESH.Intermediate
• BGP MultihomingConnecting an AS to two or more upstream links or providers using BGP for redundancy and traffic control.Intermediate
• BGP Neighbor StatesThe BGP finite state machine: Idle, Connect, Active, OpenSent, OpenConfirm and Established.Intermediate
• BGP Network StatementThe BGP command that advertises a prefix only if an exact match (prefix and mask) exists in the routing table.Intermediate
• BGP Path AttributesProperties attached to BGP routes, categorized as well-known mandatory, well-known discretionary, optional transitive and optional non-transitive.Intermediate
• BGP Regular ExpressionPattern matching used in AS-path access lists to filter or select routes by AS_PATH contents.Intermediate
• BGP Route Reflector (RR)An iBGP router allowed to re-advertise iBGP-learned routes to its clients, removing the full-mesh requirement.Intermediate
• Bidirectional Forwarding Detection (BFD)A lightweight hello protocol that detects forwarding path failures in milliseconds and notifies routing protocols.Intermediate
• Bootstrap Router (BSR)The standards-based PIMv2 mechanism for distributing RP-to-group mappings hop by hop.Advanced
• Border Gateway Protocol (BGP)The path-vector EGP (BGP-4) that exchanges reachability between autonomous systems and is the routing protocol of the Internet.Foundational
• BPDU FilterAn STP feature that stops sending and, depending on configuration, receiving BPDUs on a port.Advanced
• BPDU GuardAn STP feature that errdisables a port if it receives any BPDU, protecting PortFast edge ports.Intermediate
• Bridge ID (BID)An 8-byte STP identifier made of a 2-byte priority (with extended system ID) and the switch MAC address.Foundational
• Bridge PriorityThe configurable portion of the STP bridge ID, 0-61440 in steps of 4096, default 32768.Foundational
• Bridge Protocol Data Unit (BPDU)The STP message switches exchange to elect the root bridge and compute the loop-free topology.Intermediate
• Call Signaling MarkingMarking SIP, SCCP, H.323 and other call control traffic as CS3 so it gets protected bandwidth without priority queuing.Intermediate
• Cisco Catalyst 9800 Series Wireless Controller (C9800)Cisco's IOS XE-based wireless controller family, available as appliances, VM (9800-CL), and embedded options.Intermediate
• Cisco Catalyst CenterCisco's enterprise network controller and assurance platform, formerly Cisco DNA Center, with northbound Intent REST APIs.Intermediate
• Cisco Catalyst SD-WANCisco's software-defined WAN solution (formerly Viptela) with separate management, control, orchestration and data planes.Intermediate
• Cisco Discovery Protocol (CDP)Cisco-proprietary Layer 2 protocol that advertises device identity, platform, addresses, VLAN and capabilities to directly connected neighbors.Foundational
• Cisco Express Forwarding (CEF)Cisco's default topology-based switching mechanism using a precomputed FIB and adjacency table for fast forwarding.Intermediate
• Cisco IOS XECisco's Linux-based modular operating system for enterprise routers and switches such as Catalyst 8000 and 9000, running IOS as a daemon.Foundational
• Cisco SD-Access (SDA)Cisco's campus fabric using a LISP control plane, VXLAN data plane and TrustSec group policy, managed by Catalyst Center.Advanced
• Class of Service (CoS)The 3-bit Priority Code Point in the 802.1Q tag used for Layer 2 QoS marking (IEEE 802.1p).Foundational
• Class Selector (CS)DSCP values CS0-CS7 (multiples of 8) that preserve backward compatibility with 3-bit IP Precedence.Intermediate
• Class-Based Weighted Fair Queuing (CBWFQ)A queuing method that guarantees minimum bandwidth to user-defined traffic classes during congestion.Intermediate
• Classification and MarkingIdentifying traffic (by ACL, NBAR, DSCP, interface) and writing a QoS value into the packet so later devices can act on it.Foundational
• Committed Information Rate (CIR)The average rate a provider guarantees or a policer/shaper enforces, in bits per second.Foundational
• Conditional TrustA switch QoS setting that trusts endpoint markings only when a specific device, such as a Cisco IP phone, is detected via CDP.Intermediate
• ConvergenceThe state in which all routers have consistent, accurate routing information after a topology change.Foundational
• Count to InfinityA distance-vector routing loop problem where routers keep incrementing the metric of an unreachable route.Intermediate
• Default-Information OriginateA command that makes OSPF (or other protocols) advertise a default route into the routing domain.Intermediate
• Designated Intermediate System (DIS)The IS-IS router elected on a broadcast segment to create the pseudonode and send periodic CSNPs.Advanced
• Designated Port (DP)The port on each segment that offers the lowest cost path to the root and forwards toward that segment.Foundational
• Designated Router (DR)The OSPF router elected on a multi-access segment to form full adjacencies with all others and originate the Type 2 LSA.Intermediate
• Differentiated Services (DiffServ)A scalable QoS model that classifies and marks packets with DSCP values and applies per-hop behaviors at each router.Foundational
• Diffusing Update Algorithm (DUAL)The EIGRP algorithm that guarantees loop-free paths and selects successors and feasible successors.Intermediate
• Direct Internet Access (DIA)Sending branch Internet traffic directly out a local Internet link instead of backhauling it to a data center.Intermediate
• Distance-Vector Routing ProtocolA routing protocol class where routers share their routing tables with neighbors and know only distance and direction to destinations.Foundational
• Dynamic Multipoint VPN (DMVPN)A Cisco hub-and-spoke VPN design using mGRE, NHRP and usually IPsec that can build dynamic spoke-to-spoke tunnels.Advanced
• Dynamic Trunking Protocol (DTP)A Cisco protocol that negotiates whether a link becomes a trunk, using modes dynamic auto, dynamic desirable, trunk and access.Intermediate
• eBGP MultihopA BGP option that raises the TTL of eBGP packets so peers need not be directly connected, such as loopback peering.Intermediate
• Edge PortAn RSTP port connected to an end host that transitions directly to forwarding and generates no topology changes.Intermediate
• EIGRP AuthenticationMD5 or HMAC-SHA-256 authentication of EIGRP packets using key chains (MD5) or named-mode passwords.Intermediate
• EIGRP Composite MetricEIGRP's metric calculated from bandwidth and delay by default, with optional load and reliability via K values.Intermediate
• EIGRP Hello and Hold TimersEIGRP sends hellos every 5 seconds (60 on slow NBMA) and declares a neighbor down after the hold time (15 or 180 seconds).Intermediate
• EIGRP Named ModeHierarchical EIGRP configuration that groups all IPv4 and IPv6 settings under address families in one process.Intermediate
• EIGRP Packet TypesThe five EIGRP packet types: Hello, Update, Query, Reply and Acknowledgment (plus SIA-Query and SIA-Reply).Intermediate
• EIGRP StubAn EIGRP router configured to advertise only selected routes and to be excluded from query propagation.Intermediate
• EIGRP Summary RouteA manually configured EIGRP summary advertised out an interface, which installs a Null0 discard route with AD 5.Intermediate
• EIGRP Topology TableThe EIGRP table storing all learned routes with their FD and RD, including successors and feasible successors.Intermediate
• EIGRP VarianceAn EIGRP multiplier that allows feasible successors with an FD up to variance times the best FD to be used for load sharing.Intermediate
• Encapsulated Remote SPAN (ERSPAN)SPAN that encapsulates mirrored traffic in GRE so it can be routed across Layer 3 to a remote collector.Advanced
• Endpoint Identifier (EID)The LISP address that identifies an endpoint (host IP or MAC), independent of its network location.Advanced
• Enhanced Interior Gateway Routing Protocol (EIGRP)Cisco-developed advanced distance-vector IGP using DUAL for loop-free fast convergence; published as informational RFC 7868.Foundational
• Equal-Cost Multipath (ECMP)Installing and load sharing across multiple routes to the same prefix that have identical cost.Intermediate
• ErrdisableA Cisco port state where the switch shuts an interface due to a detected error such as BPDU guard, port security or UDLD.Intermediate
• EtherChannelCisco term for bundling multiple physical Ethernet links into one logical link for bandwidth and redundancy.Foundational
• Expedited Forwarding (EF)A DiffServ PHB (DSCP 46) for low-loss, low-latency, low-jitter traffic such as voice, usually served by a priority queue.Foundational
• Explicit Congestion Notification (ECN)A mechanism using the two low-order bits of the DS byte to signal congestion without dropping packets.Advanced
• Extended System IDThe 12-bit field in the STP bridge priority that carries the VLAN ID, allowing a unique bridge ID per VLAN with one MAC.Intermediate
• External BGP (eBGP)A BGP session between routers in different autonomous systems.Foundational
• Fabric Border NodeThe SD-Access role connecting the fabric to external networks, translating VNs and SGTs at the boundary.Advanced
• Fabric Control Plane NodeThe SD-Access role running the LISP map server and map resolver, tracking where every endpoint is attached.Advanced
• Fabric Edge NodeThe SD-Access access switch that connects endpoints, authenticates them, registers them with the control plane and provides the anycast gateway.Advanced
• Feasibility Condition (FC)EIGRP's loop-free test: a neighbor qualifies as a feasible successor only if its reported distance is less than the current feasible distance.Intermediate
• Feasible Distance (FD)The lowest total EIGRP metric from the local router to a destination, through the successor.Intermediate
• Feasible Successor (FS)An EIGRP backup neighbor whose reported distance is lower than the current feasible distance, guaranteeing a loop-free path.Intermediate
• First Hop Redundancy Protocol (FHRP)A class of protocols that provide a redundant default gateway through a shared virtual IP and MAC address.Foundational
• First In First Out (FIFO)The simplest queuing method where packets are transmitted in arrival order with no prioritization.Foundational
• Floating Static RouteA static route given a higher administrative distance than the primary route so it installs only when the primary fails.Foundational
• Forwarding Information Base (FIB)The data-plane table, derived from the RIB, used to forward packets at high speed.Intermediate
• Fully Specified Static RouteA static route that names both the exit interface and the next-hop IP address.Intermediate
• Fusion RouterA router or firewall outside an SD-Access fabric that leaks routes between virtual networks and shared services.Advanced
• Gateway Load Balancing Protocol (GLBP)Cisco-proprietary FHRP that provides gateway redundancy and load balancing using one virtual IP and multiple virtual MACs.Intermediate
• Graceful RestartA mechanism letting neighbors keep forwarding through a restarting router's control plane using preserved forwarding state.Advanced
• Hello PacketA periodic routing protocol message used to discover neighbors, verify parameters and maintain adjacencies.Foundational
• Hierarchical QoS (HQoS)A nested QoS policy where a parent policy shapes aggregate traffic and a child policy queues classes within the shaped rate.Advanced
• Hold-Down TimerA timer during which a router ignores updates with worse metrics for a route recently marked unreachable.Intermediate
• Hot Standby Router Protocol (HSRP)Cisco-proprietary FHRP with one active and one standby router sharing a virtual IP and MAC address.Foundational
• HSRP Interface TrackingReducing an HSRP router's priority when a tracked interface or object fails so the standby router can take over.Intermediate
• HSRP PreemptionAn HSRP option that lets a router with higher priority take over as active when it comes online.Foundational
• IEEE 802.1ad (Q-in-Q)A standard for stacking two VLAN tags (S-tag and C-tag) so providers can carry customer VLANs transparently.Advanced
• IEEE 802.1QThe IEEE standard for VLAN tagging that inserts a 4-byte tag with a 12-bit VLAN ID into Ethernet frames.Foundational
• IGMP SnoopingA switch feature that listens to IGMP messages to forward multicast frames only to ports with interested receivers.Intermediate
• Integrated Routing and Bridging (IRB)A logical Layer 3 interface bound to a bridge domain or VLAN, the Junos and EVPN equivalent of an SVI.Intermediate
• Integrated Services (IntServ)A QoS model that reserves resources per flow end to end using RSVP signaling.Intermediate
• Inter-VLAN RoutingRouting packets between VLANs using a router or Layer 3 switch.Foundational
• Interior Gateway Protocol (IGP)A routing protocol used to exchange routes within a single autonomous system, such as OSPF, IS-IS, EIGRP or RIP.Foundational
• Intermediate System to Intermediate System (IS-IS)A link-state IGP originally for OSI CLNS that runs directly over Layer 2 and is widely used in service provider cores.Intermediate
• Internal BGP (iBGP)A BGP session between routers in the same autonomous system.Intermediate
• Internal Spanning Tree (IST)MST instance 0, which carries BPDUs for the region and connects it to the Common and Internal Spanning Tree (CIST).Advanced
• IP MulticastOne-to-many or many-to-many delivery where a source sends a single stream to a group address and routers replicate it only where receivers exist.Foundational
• IP PrecedenceThe legacy 3-bit priority field in the IPv4 ToS byte, values 0-7, superseded by DSCP.Foundational
• IP SLACisco IOS feature that generates synthetic probes (ICMP, UDP jitter, HTTP) to measure reachability and performance.Intermediate
• IS-IS Level 1Intra-area IS-IS routing; L1 routers know only their own area and use the closest L1/L2 router for other destinations.Intermediate
• K ValuesThe EIGRP metric weights K1-K5 (plus K6 in wide metrics) that determine which components are used in the metric.Intermediate
• Key ChainA Cisco construct holding one or more numbered keys with optional lifetimes, used for routing protocol authentication.Intermediate
• Label Distribution Protocol (LDP)A protocol that distributes label bindings for IGP prefixes between MPLS neighbors.Intermediate
• Layer 3 RoamingA roam between APs in different IP subnets in which the client keeps its original IP address.Advanced
• Link Aggregation Control Protocol (LACP)IEEE 802.3ad/802.1AX protocol that negotiates link aggregation bundles; modes active and passive.Foundational
• Link Layer Discovery Protocol (LLDP)IEEE 802.1AB vendor-neutral Layer 2 neighbor discovery protocol using TLVs.Foundational
• Link-State Advertisement (LSA)An OSPF data unit describing a router's links, a network, or external and summary prefixes, flooded to build the LSDB.Intermediate
• Link-State Database (LSDB)The collection of LSAs a link-state router holds, identical among all routers in the same area.Intermediate
• Link-State Routing ProtocolA routing protocol class where every router floods topology information and independently computes shortest paths with SPF.Foundational
• Load Balancing HashThe algorithm that selects which member link of an EtherChannel or ECMP group carries a flow, based on header fields.Intermediate
• Local Preference (LOCAL_PREF)A well-known discretionary BGP attribute shared among iBGP peers; the highest value is preferred for outbound traffic from the AS.Intermediate
• Locator/ID Separation Protocol (LISP)A protocol that separates endpoint identity (EID) from location (RLOC) using a mapping system, used as the SD-Access control plane.Advanced
• Longest Prefix Match (LPM)The forwarding rule that the route with the most specific (longest) matching prefix is used, regardless of AD or metric.Foundational
• Loop GuardAn STP feature that stops a non-designated port from becoming designated when BPDUs stop arriving, preventing loops from unidirectional links.Advanced
• Loopback InterfaceA logical, always-up router interface used for management, router IDs and stable peering addresses.Foundational
• Low Latency Queuing (LLQ)CBWFQ with a strict priority queue for real-time traffic, policed during congestion to prevent starvation of other classes.Intermediate
• MetricA protocol-specific value expressing the cost of a path; within one routing protocol the lowest metric route is preferred.Foundational
• Mobility GroupA set of wireless controllers that share client context to support seamless roaming between them.Advanced
• Model-Driven Telemetry (MDT)Streaming YANG-modeled operational data from network devices to collectors, replacing periodic SNMP polling.Advanced
• Modular QoS CLI (MQC)Cisco's three-step QoS configuration framework: class-map, policy-map and service-policy.Intermediate
• MPLS LabelA 32-bit shim header containing a 20-bit label value, 3-bit Traffic Class (EXP), 1-bit bottom-of-stack flag and 8-bit TTL.Intermediate
• MST RegionA group of interconnected switches with identical MST name, revision number and VLAN-to-instance mapping.Advanced
• Multi-Exit Discriminator (MED)An optional non-transitive BGP attribute that suggests to a neighboring AS which entry point to use; lower is preferred.Intermediate
• Multicast Address RangesKey IPv4 multicast blocks: 224.0.0.0/24 link-local, 232.0.0.0/8 SSM, 233.0.0.0/8 GLOP and 239.0.0.0/8 administratively scoped.Foundational
• Multicast Listener Discovery (MLD)The IPv6 equivalent of IGMP, carried in ICMPv6, for hosts to signal multicast group membership.Intermediate
• Multimedia Conferencing MarkingMarking interactive video such as desktop and room conferencing as AF41 under RFC 4594-based designs.Intermediate
• Multiple Spanning Tree Protocol (MST)IEEE 802.1s, which maps many VLANs to a small number of RSTP-based spanning tree instances.Advanced
• Multiprotocol BGP (MP-BGP)Extensions to BGP (RFC 4760) that carry routing information for multiple address families such as IPv6, VPNv4, EVPN and multicast.Advanced
• Multiprotocol Label Switching (MPLS)A forwarding technology that switches packets using short labels instead of IP lookups, enabling VPNs, traffic engineering and fast reroute.Intermediate
• Native VLANThe VLAN whose frames are sent untagged across an 802.1Q trunk, VLAN 1 by default on Cisco.Foundational
• NETCONFThe Network Configuration Protocol (RFC 6241), an XML-based RPC protocol over SSH (port 830) for installing, manipulating, and deleting device configuration.Intermediate
• Network Entity TitleThe IS-IS router address in NSAP format, containing the area ID, system ID and NSEL of 00.Intermediate
• Network ProgrammabilityUsing software, APIs, and data models to configure, monitor, and operate networks programmatically instead of by CLI.Foundational
• Network-Based Application Recognition (NBAR2)Cisco deep packet inspection engine that identifies applications (over 1,500 protocols) for classification and visibility.Intermediate
• Next-Hop-SelfA BGP neighbor option that rewrites the NEXT_HOP to the router's own address when advertising to iBGP peers.Intermediate
• NEXT_HOP AttributeA well-known mandatory BGP attribute giving the IP address to forward toward for a prefix.Intermediate
• Nonstop Routing (NSR)A high-availability feature where the standby route processor maintains full routing protocol state so neighbors never notice a switchover.Advanced
• Northbound and Southbound APIsController interfaces: northbound APIs face applications and users, while southbound APIs face network devices.Foundational
• Not-So-Stubby Area (NSSA)An OSPF stub-like area that blocks Type 5 LSAs but allows a local ASBR to inject externals as Type 7 LSAs.Advanced
• Null0 InterfaceA virtual Cisco interface that discards traffic routed to it, used for summary and blackhole routes.Intermediate
• Object TrackingCisco feature that monitors the state of an interface, route or IP SLA and lets other features react to it.Intermediate
• Open Shortest Path First (OSPF)An open-standard link-state IGP that uses areas, LSAs and Dijkstra's SPF algorithm with a cost metric.Foundational
• Origin AttributeA well-known mandatory BGP attribute indicating how a route entered BGP: IGP (i), EGP (e) or incomplete (?).Intermediate
• OSPF AreaA logical grouping of OSPF routers and links that share an LSDB, limiting flooding and SPF scope.Foundational
• OSPF Area 0The OSPF backbone area to which all other areas must connect and through which all inter-area traffic passes.Foundational
• OSPF Area RangeInter-area summarization configured on an ABR to advertise one Type 3 LSA for a block of intra-area routes.Intermediate
• OSPF AuthenticationMethods for authenticating OSPF packets: null, plaintext, MD5 and HMAC-SHA with key chains.Intermediate
• OSPF CostThe OSPF interface metric, calculated as reference bandwidth divided by interface bandwidth, summed along a path.Foundational
• OSPF External Route TypeOSPF E1 and E2 routes: E2 (default) keeps only the redistributed metric, while E1 adds internal cost to reach the ASBR.Intermediate
• OSPF Hello and Dead IntervalsOSPF timers: how often hellos are sent and how long to wait without hellos before declaring a neighbor down.Foundational
• OSPF MTU MismatchA condition where OSPF neighbors have different interface MTUs, leaving the adjacency stuck in ExStart or Exchange.Intermediate
• OSPF Neighbor StatesThe progression an OSPF adjacency follows: Down, Attempt, Init, 2-Way, ExStart, Exchange, Loading, Full.Intermediate
• OSPF Network StatementAn OSPF configuration command that uses an address and wildcard mask to select interfaces and assign them to an area.Foundational
• OSPF Network TypesOSPF interface modes - broadcast, non-broadcast, point-to-point, point-to-multipoint and loopback - controlling DR election, timers and neighbor discovery.Intermediate
• OSPF Packet TypesThe five OSPF packet types: Hello, Database Description (DBD), Link-State Request (LSR), Link-State Update (LSU) and Link-State Acknowledgment.Intermediate
• OSPF Path Selection OrderOSPF prefers intra-area over inter-area over E1/N1 over E2/N2 routes for the same prefix, before comparing cost.Intermediate
• OSPF PriorityAn interface value from 0 to 255 (default 1) used in DR/BDR election; 0 makes the router ineligible.Foundational
• OSPF Stub AreaAn OSPF area that blocks Type 4 and Type 5 external LSAs and receives a default route from the ABR instead.Intermediate
• OSPF Summary AddressAn ASBR command that summarizes external (Type 5 or Type 7) routes redistributed into OSPF.Intermediate
• OSPF Totally Stubby AreaA Cisco OSPF area type that blocks Type 3, 4 and 5 LSAs, leaving only a default route from the ABR.Intermediate
• OSPF Type 1 Router LSAThe LSA every OSPF router originates in each area, describing its links, costs and neighbors; flooded within the area only.Intermediate
• OSPF Type 2 Network LSAThe LSA originated by the DR on a multi-access segment, listing all routers attached to that transit network.Intermediate
• OSPF Type 3 Summary LSAThe LSA an ABR originates to advertise prefixes from one area into another.Intermediate
• OSPF Type 4 ASBR Summary LSAAn LSA originated by an ABR to tell routers in another area how to reach an ASBR.Advanced
• OSPF Type 5 External LSAAn LSA originated by an ASBR to advertise routes redistributed from outside OSPF, flooded throughout all normal areas.Intermediate
• OSPF Type 7 NSSA LSAAn external LSA originated by an ASBR inside an NSSA, converted to Type 5 by the NSSA ABR.Advanced
• OSPF Virtual LinkA logical link through a transit area that connects a remote area or partitioned backbone to area 0.Advanced
• OSPFv3The version of OSPF for IPv6 (and, with address families, IPv4) defined in RFC 5340.Intermediate
• Overlay Management Protocol (OMP)The TCP-based Cisco SD-WAN control protocol, running inside DTLS/TLS tunnels, that distributes routes, TLOCs, keys and policy.Advanced
• Passive InterfaceAn interface on which a routing protocol advertises the connected network but does not send hellos or form adjacencies.Foundational
• Path-Vector Routing ProtocolA routing protocol class that advertises the full sequence of autonomous systems a route has traversed, used for loop prevention.Intermediate
• Per-Hop Behavior (PHB)The forwarding treatment a DiffServ router applies to packets based on their DSCP marking.Intermediate
• Per-VLAN Spanning Tree Plus (PVST+)Cisco's STP variant that runs a separate 802.1D instance per VLAN, allowing per-VLAN root placement and load sharing.Foundational
• PIM Dense Mode (PIM-DM)A push-model multicast protocol that floods traffic everywhere and prunes branches without receivers.Intermediate
• PIM Designated RouterThe PIM router elected on a multiaccess segment (highest DR priority, then highest IP) to send joins and registers for local hosts.Advanced
• PIM Sparse Mode (PIM-SM)A pull-model multicast protocol where routers explicitly join a shared tree rooted at a rendezvous point and may switch to a source tree.Intermediate
• Poison ReverseA rule where a router advertises a route back toward its source with an infinite metric, overriding split horizon.Intermediate
• PolicingA QoS action that enforces a rate limit by dropping or remarking traffic that exceeds it, without buffering.Foundational
• Policy-Based Routing (PBR)Forwarding packets based on criteria other than destination, such as source address or application, using a route map.Intermediate
• Port Aggregation Protocol (PAgP)Cisco-proprietary EtherChannel negotiation protocol with modes desirable and auto.Foundational
• Port-Channel InterfaceThe logical interface representing an EtherChannel bundle on Cisco devices, where Layer 2 or Layer 3 settings are applied.Foundational
• PortFastA Cisco feature that moves an access port directly to forwarding, skipping listening and learning.Foundational
• Prefix ListA Cisco filter that matches routes by prefix and prefix length range, preferred over ACLs for route filtering.Intermediate
• Priority Queue Provisioning RuleThe Cisco design guideline that strict-priority (LLQ) traffic should not exceed about 33 percent of link capacity.Advanced
• Private AS NumberASN ranges 64512-65534 (2-byte) and 4200000000-4294967294 (4-byte) reserved for private use and not routed on the Internet.Intermediate
• Private VLAN (PVLAN)A feature that subdivides a primary VLAN into isolated and community secondary VLANs that share one subnet.Advanced
• Process SwitchingThe slowest Cisco forwarding method, where the CPU performs a full routing lookup for every packet.Intermediate
• Proposal and AgreementThe RSTP handshake on point-to-point links that lets a designated port move to forwarding immediately.Advanced
• Protocol Independent Multicast (PIM)The family of multicast routing protocols that build distribution trees using the existing unicast routing table for RPF checks.Intermediate
• QoS Trust BoundaryThe point in the network where QoS markings from endpoints start being trusted rather than rewritten.Intermediate
• Quality of Service (QoS)Tools that classify, mark, queue, shape and drop traffic to give applications appropriate bandwidth, delay, jitter and loss.Foundational
• Random Early Detection (RED)A congestion avoidance mechanism that randomly drops packets as average queue depth rises between minimum and maximum thresholds.Intermediate
• Rapid PVST+Cisco's per-VLAN implementation of RSTP (802.1w), the default STP mode on current Catalyst switches.Intermediate
• Rapid Spanning Tree Protocol (RSTP)IEEE 802.1w, a faster STP that uses proposal/agreement handshakes, edge ports and alternate ports to converge in seconds or less.Intermediate
• Recursive Route LookupResolving a route's next-hop address by performing another routing table lookup to find the outgoing interface.Intermediate
• Reference BandwidthThe bandwidth value OSPF divides by interface bandwidth to calculate cost, 100 Mbps by default.Foundational
• Remote SPAN (RSPAN)SPAN that transports mirrored traffic across a Layer 2 network in a dedicated RSPAN VLAN to a remote switch.Advanced
• Rendezvous Point (RP)The PIM-SM router where sources and receivers meet; it roots the shared tree for a group.Intermediate
• Reported Distance (RD)The EIGRP metric a neighbor advertises for its own path to a destination; also called advertised distance.Intermediate
• Resource Reservation Protocol (RSVP)A signaling protocol (IP protocol 46) that reserves resources along a path, used by IntServ and MPLS TE.Advanced
• RESTCONFAn HTTP-based protocol (RFC 8040) that provides a REST-like interface to YANG-modeled data, using XML or JSON over HTTPS.Intermediate
• Reverse Path Forwarding Check (RPF)The multicast loop-prevention check that accepts a packet only if it arrives on the interface the router would use to reach the source (or RP).Intermediate
• RFC 4594 Service ClassesIETF configuration guidelines that map application classes such as VoIP, video, signaling and bulk data to recommended DSCP values.Advanced
• Root BridgeThe switch with the lowest bridge ID, which acts as the reference point of the STP topology; all its ports are designated.Foundational
• Root GuardAn STP feature that prevents a port from becoming a root port; superior BPDUs place it in root-inconsistent state.Intermediate
• Root Port (RP)The single port on each non-root switch with the lowest cost path to the root bridge.Foundational
• Route MapAn ordered Cisco IOS policy construct of permit/deny sequences with match and set clauses, used for filtering, redistribution, PBR and BGP policy.Intermediate
• Route PoisoningAdvertising a failed route with an infinite metric so neighbors immediately remove it instead of waiting for it to age out.Intermediate
• Route RedistributionInjecting routes learned from one routing source into another routing protocol.Intermediate
• Route RefreshA BGP capability that lets a router ask a peer to resend its routes so new inbound policy can be applied without resetting the session.Intermediate
• Route SummarizationAdvertising a single aggregate prefix that covers multiple more specific routes to reduce table size and contain instability.Intermediate
• Routed PortA physical switch port converted to Layer 3 with no switchport, behaving like a router interface.Intermediate
• Router ID (RID)A 32-bit identifier, written as an IPv4 address, that uniquely identifies a router within OSPF, EIGRP or BGP.Foundational
• Routing Information Base (RIB)The control-plane table holding the best routes chosen from all routing sources, used to build the forwarding table.Intermediate
• Routing Locator (RLOC)The LISP address of the tunnel router behind which an EID resides, typically a loopback in the underlay.Advanced
• Routing TableThe router's table of best known paths to destination prefixes, built from connected, static and dynamic routing sources.Foundational
• Scalable Group Tag (SGT)A 16-bit Cisco TrustSec tag that identifies a group of users or devices for role-based policy regardless of IP address.Advanced
• SD-WAN ControllerThe Cisco Catalyst SD-WAN control plane element (formerly vSmart) that distributes routes, TLOCs and policies to WAN Edges via OMP.Intermediate
• SD-WAN ManagerThe Cisco Catalyst SD-WAN management plane (formerly vManage): GUI and API for configuration, templates, monitoring and policy.Intermediate
• SD-WAN Service VPNA Cisco SD-WAN segment (VRF) on the LAN side carrying user traffic, numbered 1-511 except the reserved VPN 0 and VPN 512.Intermediate
• SD-WAN ValidatorThe Cisco Catalyst SD-WAN orchestration element (formerly vBond) that authenticates devices and helps them discover controllers and traverse NAT.Intermediate
• Seed MetricThe initial metric assigned to routes redistributed into a routing protocol.Intermediate
• Segment Routing (SR)A source-routing architecture where the ingress node encodes a path as an ordered list of segments, with no per-flow state in the core.Advanced
• ShapingA QoS action that buffers excess traffic to send it at a configured rate, smoothing bursts.Foundational
• Shared TreeA multicast distribution tree rooted at the RP and used by all sources for a group, written (*,G).Intermediate
• Shortest Path First Algorithm (SPF)Dijkstra's algorithm, used by OSPF and IS-IS to compute a loop-free shortest path tree from the LSDB.Intermediate
• Shortest Path Tree (SPT)A multicast source tree rooted at the source, written (S,G), giving the optimal path from source to receivers.Intermediate
• Simple Network Management Protocol (SNMP)A traditional UDP-based protocol for monitoring and managing network devices using MIBs, polling (ports 161) and traps (port 162).Foundational
• Software-Defined Networking (SDN)A network architecture that separates the control plane from the data plane and centralizes control in software controllers with programmable APIs.Foundational
• Source-Specific Multicast (SSM)A PIM mode in which receivers join a specific (S,G) channel directly, eliminating the RP and shared tree.Intermediate
• Spanning Tree Protocol (STP)IEEE 802.1D protocol that prevents Layer 2 loops by electing a root bridge and blocking redundant paths.Foundational
• Split HorizonA loop-prevention rule that stops a router from advertising a route out the interface on which it was learned.Intermediate
• StackWise VirtualCisco Catalyst 9000 technology that combines two switches into one logical switch with a single control plane.Advanced
• Stateful Switchover (SSO)A Cisco high-availability feature where the standby route processor is kept synchronized so it can take over without resetting interfaces.Advanced
• Storm ControlA switch feature that limits broadcast, multicast or unknown unicast traffic on a port to a threshold.Intermediate
• STP Path CostThe cost STP assigns to a port based on its speed, summed toward the root to choose root and designated ports.Intermediate
• STP Port States802.1D states: blocking, listening, learning, forwarding and disabled; RSTP collapses these to discarding, learning and forwarding.Foundational
• STP TimersThe 802.1D timers: hello time 2 s, forward delay 15 s and max age 20 s, all dictated by the root bridge.Intermediate
• Stuck in Active (SIA)An EIGRP condition where a router waits too long for replies to queries, eventually resetting neighbor adjacencies.Advanced
• SuccessorThe EIGRP neighbor offering the lowest-metric loop-free path to a destination; its route is installed in the routing table.Intermediate
• Switch StackingConnecting multiple switches with dedicated stack cables so they operate as one logical switch with one management plane.Intermediate
• Switched Virtual Interface (SVI)A virtual Layer 3 interface on a switch representing a VLAN, used for inter-VLAN routing or management.Foundational
• Tail DropThe default congestion behavior where packets arriving at a full queue are discarded.Foundational
• TCP Global SynchronizationA condition where many TCP flows experience drops simultaneously, all reduce their windows, then ramp up together, causing oscillating link utilization.Intermediate
• Telemetry Subscription ModesThe ways telemetry sessions are established and data is sent: dial-in vs dial-out, and periodic vs on-change.Advanced
• Ternary Content-Addressable Memory (TCAM)Hardware memory that matches on 0, 1 or don't-care bits, used for ACLs, QoS and longest-prefix route lookups.Advanced
• Token BucketThe algorithm policers and shapers use: tokens accumulate at the CIR and each transmitted byte consumes one token.Intermediate
• Topology Change Notification (TCN)An 802.1D BPDU sent toward the root when a port changes state, causing switches to shorten MAC aging to forward delay.Advanced
• Transit ASAn autonomous system that carries traffic between two other autonomous systems.Intermediate
• Transport Locator (TLOC)A Cisco SD-WAN identifier of a WAN Edge transport attachment point: system IP, color and encapsulation.Advanced
• Trunk PortA switch port that carries multiple VLANs over one link, identifying them with 802.1Q tags.Foundational
• Two-Rate Three-Color Marker (trTCM)A policer (RFC 2698) with CIR and PIR that colors traffic conform (green), exceed (yellow) or violate (red).Advanced
• Unequal-Cost Load BalancingDistributing traffic across paths with different metrics, natively supported by EIGRP through the variance command.Intermediate
• Unidirectional Link Detection (UDLD)A Cisco Layer 2 protocol that detects links where traffic flows in only one direction, common with fiber faults.Advanced
• Unknown Unicast FloodingForwarding a frame out all ports in its VLAN (except the source) when the destination MAC is not in the MAC table.Intermediate
• Update-SourceA BGP neighbor option that sets the source interface (usually a loopback) for the TCP session.Intermediate
• Virtual Extensible LAN (VXLAN)An overlay encapsulation (RFC 7348) that carries Layer 2 frames inside UDP/IP packets, identified by a 24-bit VNI.Intermediate
• Virtual Local Area Network (VLAN)A logical Layer 2 broadcast domain created on switches, independent of physical location.Foundational
• Virtual Network (VN)An SD-Access macro-segment implemented as a VRF across the fabric, isolating groups such as employees, guests and IoT.Advanced
• Virtual Router Redundancy Protocol (VRRP)IETF-standard FHRP (RFC 5798 for VRRPv3) with one master and backups sharing a virtual IP that may be a real interface address.Foundational
• Virtual Routing and Forwarding (VRF)A technology that creates multiple independent routing tables on one router so overlapping or separated networks coexist.Intermediate
• VLAN Trunking Protocol (VTP)A Cisco protocol that propagates VLAN definitions from a server to other switches in the same VTP domain.Intermediate
• VLAN Trunking Protocol PruningA VTP feature that stops flooding of broadcast and unknown traffic for a VLAN across trunks to switches with no ports in that VLAN.Intermediate
• Voice QoS RequirementsGuidelines for acceptable voice quality: one-way delay under 150 ms, jitter under 30 ms and packet loss under 1 percent.Foundational
• Voice VLANA separate VLAN on an access port for IP phone traffic, which the phone tags while passing PC traffic untagged.Foundational
• VRF-LiteUsing VRFs for Layer 3 segmentation without MPLS or MP-BGP, by carrying each VRF on separate interfaces or subinterfaces hop by hop.Intermediate
• VXLAN Network Identifier (VNI)The 24-bit segment ID in the VXLAN header that identifies a Layer 2 (L2VNI) or Layer 3 (L3VNI) virtual network.Intermediate
• WeightA Cisco-proprietary BGP value local to one router; the highest weight is preferred first in best-path selection.Intermediate
• Weighted Random Early Detection (WRED)RED with different drop profiles per IP Precedence or DSCP, so lower-priority packets are dropped earlier.Intermediate
• Well-Known BGP CommunitiesReserved communities with standard meaning: NO_EXPORT, NO_ADVERTISE, NO_EXPORT_SUBCONFED (local-AS) and others.Intermediate
• Wildcard MaskAn inverse mask where 0 bits must match and 1 bits are ignored, used in ACLs and OSPF/EIGRP network statements.Foundational
• YANGYet Another Next Generation (RFC 7950), a data modeling language that defines the structure of configuration and operational data for network devices.Intermediate
• Zero-Touch Provisioning (ZTP)Automated onboarding where a new device obtains configuration and software from a server without manual console work.Intermediate