Juniper JNCIA-Junos: key terms

Flashcards for this exam Juniper JNCIA-Junos guide Class dates

• Access LayerThe edge layer of a hierarchical network where end devices connect.Intermediate
• Access PortA switch port that carries traffic for a single data VLAN (plus optionally a voice VLAN) without tagging.Foundational
• Address Resolution Protocol (ARP)The protocol (RFC 826) that resolves a known IPv4 address to the corresponding MAC address on the local network.Foundational
• Aggregate RouteA Junos summary route defined under routing-options aggregate that is active when at least one contributing more-specific route exists.Intermediate
• Aggregated EthernetJuniper Junos link aggregation interface (aeX) that bundles physical links with or without LACP.Intermediate
• Application Layer (L7)OSI Layer 7 (and top layer of TCP/IP), which provides network services directly to user applications.Foundational
• Broadcast DomainThe set of devices that receive each other's Layer 2 broadcasts; bounded by routers or by VLANs.Foundational
• Candidate ConfigurationThe Junos working copy of the configuration edited in configuration mode, which becomes active only after commit.Foundational
• Classless Inter-Domain Routing (CIDR)The addressing scheme (RFC 4632) that replaced classful addressing by allowing any prefix length and route aggregation.Foundational
• Collapsed CoreA two-tier design in which the core and distribution layers are combined in the same devices.Intermediate
• Connected RouteA route automatically installed for the subnet of an interface that is up/up and has an IP address.Foundational
• Core LayerThe backbone layer of a hierarchical network that provides fast, redundant transport between distribution blocks.Intermediate
• Data Link Layer (L2)OSI Layer 2, which delivers frames between nodes on the same local network using physical (MAC) addresses.Foundational
• Default RouteThe route 0.0.0.0/0 (or ::/0 in IPv6) that matches any destination not covered by a more specific route.Intermediate
• DHCPv6The IPv6 version of DHCP, which can assign addresses (stateful) or just options such as DNS servers (stateless).Intermediate
• Differentiated Services Code Point (DSCP)A 6-bit value in the IP header used to mark packets for quality-of-service treatment.Intermediate
• Discard RouteA route that silently drops matching packets, used to anchor aggregates and prevent loops (Junos discard next hop).Intermediate
• Distribution LayerThe aggregation layer of a hierarchical network that connects access switches and enforces policy, routing and summarization.Intermediate
• Dual StackRunning IPv4 and IPv6 simultaneously on the same devices and network.Foundational
• Dynamic NATNAT that maps inside addresses to public addresses drawn from a pool on a first-come, first-served, one-to-one basis.Foundational
• Edge PortAn RSTP port connected to an end host that transitions directly to forwarding and generates no topology changes.Intermediate
• EncapsulationThe process of each layer wrapping data from the layer above with its own header (and sometimes trailer) as it moves down the stack.Foundational
• Ephemeral PortsShort-lived client-side source ports assigned by the operating system for outgoing connections, typically 49152-65535.Foundational
• EtherChannelCisco term for bundling multiple physical Ethernet links into one logical link for bandwidth and redundancy.Foundational
• Ethernet FrameThe Layer 2 unit Ethernet uses, containing destination MAC, source MAC, EtherType or length, payload and FCS.Foundational
• EtherTypeA 2-byte Ethernet II field identifying the protocol carried in the frame's payload.Intermediate
• Firewall FilterA Junos stateless packet filter, like an ACL, whose terms match packets (from) and apply actions such as accept, discard, count or policer.Intermediate
• Forwarding Information Base (FIB)The data-plane table, derived from the RIB, used to forward packets at high speed.Intermediate
• FragmentationSplitting an IP packet into smaller pieces so it can cross a link with a smaller MTU, then reassembling it at the destination.Intermediate
• Frame Check Sequence (FCS)The 4-byte Ethernet trailer containing a CRC-32 value used to detect frame corruption.Foundational
• Generic Routing Encapsulation (GRE)A Cisco-developed tunneling protocol (IP protocol 47) that encapsulates almost any network-layer protocol in IP.Intermediate
• Global Unicast Address (GUA)A globally routable IPv6 address, currently allocated from 2000::/3.Foundational
• ICMPv6The IPv6 version of ICMP (next header 58), which handles errors, diagnostics, Neighbor Discovery and multicast listener discovery.Intermediate
• IEEE 802.1QThe IEEE standard for VLAN tagging that inserts a 4-byte tag with a 12-bit VLAN ID into Ethernet frames.Foundational
• 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
• 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
• Internet Control Message Protocol (ICMP)The Layer 3 protocol (IP protocol 1) used for error reporting and diagnostics, such as ping and traceroute.Foundational
• Internet Protocol version 6 (IPv6)The successor to IPv4, using 128-bit addresses written in hexadecimal, defined in RFC 8200.Foundational
• IP Protocol NumberThe value in the IPv4 Protocol field (or IPv6 Next Header) that identifies the encapsulated upper-layer protocol.Intermediate
• IPv4 HeaderThe 20- to 60-byte header at the front of every IPv4 packet carrying addressing and control fields.Intermediate
• IPv6 Address CompressionRules for shortening IPv6 addresses: omit leading zeros in each hextet and replace one longest run of all-zero hextets with ::.Foundational
• IPv6 Address NotationIPv6 addresses are written as eight groups of four hexadecimal digits separated by colons, with a /prefix length.Foundational
• IPv6 HeaderThe fixed 40-byte header of an IPv6 packet, with eight fields and optional extension headers chained after it.Intermediate
• IPv6 Link-Local Address (LLA)An IPv6 address in fe80::/10, automatically configured on every IPv6 interface and valid only on the local link.Foundational
• IPv6 SubnettingDividing an IPv6 prefix into smaller prefixes, normally on nibble boundaries and almost always ending with /64 LANs.Intermediate
• Junos Active Route SelectionThe Junos process of choosing one active route per prefix: lowest preference, then protocol-specific tie-breakers.Intermediate
• Junos Commit ModelThe Junos process of validating and activating the candidate configuration with commit, with options such as commit check, commit confirmed and commit at.Foundational
• Junos Default Routing PoliciesBuilt-in Junos policies applied at the end of each protocol's policy chain when no explicit policy accepts or rejects a route.Intermediate
• Junos OSJuniper Networks' network operating system, built on a FreeBSD-derived kernel (or Linux in Junos OS Evolved) with a single code train across platforms.Foundational
• Junos Policy ChainThe ordered list of policies applied to a protocol, evaluated until a terminating action (accept or reject) is reached, ending with the default policy.Intermediate
• Junos RollbackThe Junos command that loads a previously committed configuration (rollback 0-49) into the candidate.Foundational
• Junos Routing PolicyJunos import/export policy-statements whose terms use from (match) and then (action) clauses to control routes in and out of routing tables.Intermediate
• Junos Routing TablesDefault Junos tables such as inet.0 (IPv4 unicast), inet.3 (MPLS next hops), inet6.0 (IPv6), mpls.0 (labels) and bgp.l3vpn.0 (VPN routes).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
• 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
• Loopback InterfaceA logical, always-up router interface used for management, router IDs and stable peering addresses.Foundational
• MAC Address TableThe switch table mapping learned source MAC addresses to ports and VLANs, used for frame forwarding (CAM table).Foundational
• Maximum Transmission Unit (MTU)The largest Layer 3 packet, in bytes, that a link can carry without fragmentation; 1500 bytes on standard Ethernet.Foundational
• Modified EUI-64A method that builds a 64-bit IPv6 interface ID from a 48-bit MAC address by inserting fffe in the middle and flipping the seventh bit.Intermediate
• Multilayer SwitchA switch that can also perform Layer 3 routing (and sometimes higher-layer functions) in hardware.Foundational
• 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
• NAT64A translation mechanism that lets IPv6-only clients reach IPv4-only servers by mapping IPv4 addresses into an IPv6 prefix.Advanced
• Native VLANThe VLAN whose frames are sent untagged across an 802.1Q trunk, VLAN 1 by default on Cisco.Foundational
• Neighbor Advertisement (NA)An ICMPv6 type 136 message replying to a Neighbor Solicitation with the sender's link-layer address, or announcing a change.Intermediate
• Neighbor Discovery Protocol (NDP)The ICMPv6-based protocol (RFC 4861) that performs address resolution, router discovery, prefix discovery and duplicate address detection in IPv6.Intermediate
• Neighbor Solicitation (NS)An ICMPv6 type 135 message used to find a neighbor's MAC address, verify reachability, or detect duplicate addresses.Intermediate
• Network Address Translation (NAT)A function that rewrites IP addresses (and often ports) in packet headers as traffic passes through a router or firewall.Foundational
• Network Layer (L3)OSI Layer 3, which provides logical addressing and routing of packets between different networks.Foundational
• 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
• Open Systems Interconnection Model (OSI model)A seven-layer ISO reference model that describes how data moves from an application on one host to an application on another.Foundational
• 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 CostThe OSPF interface metric, calculated as reference bandwidth divided by interface bandwidth, summed along a path.Foundational
• Packet Forwarding Engine (PFE)The Junos data plane component, usually ASIC based, that forwards transit traffic using the forwarding table and applies filters, policers and CoS.Foundational
• Passive InterfaceAn interface on which a routing protocol advertises the connected network but does not send hellos or form adjacencies.Foundational
• Path MTU Discovery (PMTUD)A technique a host uses to find the smallest MTU along a path by sending packets with fragmentation disallowed and reacting to ICMP errors.Intermediate
• Point-to-Point Protocol (PPP)A Layer 2 protocol for direct links that provides framing, authentication (PAP or CHAP) and network-layer negotiation.Intermediate
• Point-to-Point SubnetA subnet sized for exactly two devices, traditionally a /30 and now often a /31 in IPv4 or /127 in IPv6.Intermediate
• Port Address Translation (PAT)NAT that maps many inside addresses to one (or a few) public addresses by tracking unique source port numbers; also called NAT overload.Foundational
• Port NumberA 16-bit number (0-65535) that identifies a specific application or service on a host at Layer 4.Foundational
• Prefix LengthThe number of leading network bits in an address, written after a slash, as in /24 or /64.Foundational
• Protocol Data Unit (PDU)The name for the unit of data at a given layer, such as bits, frame, packet, segment or data.Foundational
• Proxy ARPA router feature that answers ARP requests on behalf of hosts on other networks, letting hosts without a proper gateway still communicate.Advanced
• 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
• Request for Comments (RFC)The IETF document series that publishes Internet standards, best practices and informational specifications.Foundational
• Rescue ConfigurationA known-good Junos configuration saved by the administrator for recovery, loadable with rollback rescue.Foundational
• Root BridgeThe switch with the lowest bridge ID, which acts as the reference point of the STP topology; all its ports are designated.Foundational
• Route FilterA Junos policy match condition that selects routes by prefix and match type: exact, orlonger, longer, upto, through and prefix-length-range.Intermediate
• Route PreferenceJunos term for administrative distance: a 0-4294967295 value where the lower preference wins between route sources.Intermediate
• Router Advertisement (RA)An ICMPv6 type 134 message routers send periodically and in response to RS, advertising prefixes, the default gateway and configuration flags.Intermediate
• Router ID (RID)A 32-bit identifier, written as an IPv4 address, that uniquely identifies a router within OSPF, EIGRP or BGP.Foundational
• Router Solicitation (RS)An ICMPv6 type 133 message a host sends to ff02::2 asking routers to send a Router Advertisement immediately.Intermediate
• Routing Engine (RE)The Junos control plane component that runs routing protocols, the CLI and management, and builds the forwarding table.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 Information Protocol (RIP)A distance-vector IGP that uses hop count as its metric, with a 15-hop maximum and 30-second periodic updates.Foundational
• Routing InstanceA Junos construct that creates a separate routing table and set of interfaces, with types including virtual-router, vrf, forwarding and evpn/mac-vrf.Intermediate
• Routing TableThe router's table of best known paths to destination prefixes, built from connected, static and dynamic routing sources.Foundational
• Sequence NumberA 32-bit TCP header field that numbers the bytes in a stream so the receiver can reorder data and detect loss.Intermediate
• Show Interfaces CommandThe Cisco IOS command that displays an interface's status, speed, duplex, counters and errors.Foundational
• Solicited-Node Multicast AddressA multicast address (ff02::1:ffXX:XXXX) formed from the last 24 bits of a unicast address, used for efficient address resolution.Advanced
• Spanning Tree Protocol (STP)IEEE 802.1D protocol that prevents Layer 2 loops by electing a root bridge and blocking redundant paths.Foundational
• Spine-and-Leaf ArchitectureA two-tier data center design in which every leaf switch connects to every spine switch, giving predictable, low-latency paths.Intermediate
• Stateful DHCPv6A DHCPv6 mode in which the server assigns IPv6 addresses and tracks leases, signaled by the RA M flag.Intermediate
• Stateless Address Autoconfiguration (SLAAC)An IPv6 method in which hosts build their own addresses from a router-advertised /64 prefix plus a self-generated interface ID.Foundational
• Stateless DHCPv6A mode in which hosts use SLAAC for addresses but obtain other settings, such as DNS servers and domain name, from a DHCPv6 server.Intermediate
• Static NATA one-to-one, permanent mapping between a private (inside local) address and a public (inside global) address.Foundational
• Static RouteA manually configured route to a destination prefix through a next-hop address or exit interface.Foundational
• SubnettingDividing a larger IP network into smaller subnets by borrowing host bits for the network portion.Foundational
• SupernettingCombining multiple contiguous networks into one larger prefix with a shorter mask.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
• TCP FlagsSingle-bit control fields in the TCP header (SYN, ACK, FIN, RST, PSH, URG, ECE, CWR) that signal connection state and handling.Intermediate
• TCP/IP ModelThe four-layer model of the Internet protocol suite: Link (Network Access), Internet, Transport and Application.Foundational
• Three-Tier ArchitectureA hierarchical campus design with core, distribution and access layers, each with distinct roles.Intermediate
• Three-Way HandshakeThe SYN, SYN-ACK, ACK exchange TCP uses to establish a connection and synchronize sequence numbers.Foundational
• Time to Live (TTL)An 8-bit IPv4 header field decremented by each router; when it reaches zero the packet is discarded to prevent endless looping.Foundational
• Transmission Control Protocol (TCP)A connection-oriented Layer 4 protocol that provides reliable, ordered, error-checked delivery of a byte stream.Foundational
• Transport Layer (L4)OSI Layer 4, which provides host-to-host delivery, segmentation, port addressing and optionally reliability.Foundational
• Trunk PortA switch port that carries multiple VLANs over one link, identifying them with 802.1Q tags.Foundational
• TunnelingEncapsulating one protocol's packets inside another protocol so they can cross a network that does not support them natively.Intermediate
• User Datagram Protocol (UDP)A connectionless Layer 4 protocol that sends datagrams with minimal overhead and no delivery, ordering or retransmission guarantees.Foundational
• Variable Length Subnet Mask (VLSM)Using different subnet mask lengths within the same address space to match each subnet's size to its host requirement.Intermediate
• Virtual ChassisJuniper technology that interconnects multiple EX or QFX switches to be managed as a single logical device.Intermediate
• Virtual Local Area Network (VLAN)A logical Layer 2 broadcast domain created on switches, independent of physical location.Foundational