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What you will learn in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

Fundamentals and Protocols

by Jeremy McDowell

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Chapter by chapter

Concepts explained in this book

• spanning tree protocolThe spanning tree algorithm is the procedure for electing a root bridge and selecting root and designated ports to create a loop-free spanning-tree topology.
• IP addressAn IP address is a network-layer identifier assigned to a host or interface for packet delivery across interconnected networks.
• prefix lengthA prefix length is the number of leading bits in an IP address that constitute its network portion, written in slash notation such as /24.
• netmaskA netmask is a 32-bit value paired with an IPv4 address to identify which address bits belong to the network portion and which belong to the host portion.
• bridge protocol data unitA bridge protocol data unit is a control message exchanged by spanning-tree-enabled switches to communicate topology information and determine port roles.
• router idAn OSPF router ID is a unique 32-bit identifier used to identify an OSPF router and break ties in designated-router elections.
• port numberA port number is a transport-layer identifier ranging from 0 to 65535 that directs network data to a particular application process on a host.
• subnetworkA subnet is a logical subdivision of an IPv4 network address space with its own network address and prefix length.
• mac addressA MAC address is a 48-bit link-layer address assigned to a network-device port, normally by the device manufacturer, for local hop-to-hop delivery.
• TCP/IP protocol suiteThe TCP/IP model is a layered conceptual framework that describes how network communication functions across application, transport, network, data-link, and physical layers.
• access control entryAn access control entry is an ordered rule in an access control list that specifies packet-matching conditions and an action such as permitting or denying traffic.
• trunk linkA trunk port is a network interface that carries traffic for multiple VLANs, typically using VLAN tags to identify them.
• network portionThe network portion is the leading part of an IP address that identifies the network to which the addressed host belongs.
• root bridgeA root bridge is the spanning-tree switch selected as the reference point for calculating paths in a Layer 2 topology.
• IPv6IPv6 is the sixth version of the Internet Protocol, using 128-bit network addresses written in hexadecimal notation.
• equal-cost multipath routingEqual-cost multipath routing forwards or distributes traffic across multiple routes to the same destination when those routes have equal routing cost.
• etherchannelA Layer 3 EtherChannel is a logical link aggregation of routed ports that forwards packets at the network layer.
• blocking stateThe blocking state, called the discarding state in RSTP, is a spanning-tree port state in which normal data frames are not forwarded or learned while control messages may still be processed.
• bridge identifierA bridge identifier, or bridge ID, is a 64-bit value that identifies a switch within a spanning-tree instance and is advertised in bridge protocol data units.
• transport layerThe transport layer is the network-model layer that delivers data to a specific application process on a destination host.
• physical layerThe Physical Layer is a networking model layer that defines the transmission of raw signals and bits over a physical medium.
• link-state databaseA link-state database is an in-memory data structure containing the network topology information used by a link-state routing protocol to calculate routes.
• static routeIPv6 static routing is a routing method in which IPv6 routes are manually configured on routers.
• native vlanA native VLAN is the VLAN assigned to untagged traffic received on a trunk port and the VLAN whose forwarded traffic is sent untagged on that trunk.
• broadcast addressA broadcast address is the last IPv4 address in a network, with every host-portion bit set to one, for delivery to all hosts in that network.
• dynamic routingDynamic routing is a routing method in which routers exchange reachability information through routing protocols and automatically build routing tables.
• access control listA standard access control list is an IPv4 access control list that filters traffic primarily by source IP address.
• OSPF hello timerAn OSPF hello timer is the interval between successive OSPF hello messages sent by an interface.
• host routeA host route is a route to a single destination IP address, represented in IPv6 by a /128 prefix length.
• data link layerThe data link layer is the network-model layer that provides delivery between adjacent nodes over a shared physical medium.
• subnettingIPv6 subnetting is the division of an IPv6 address block into smaller subnetworks by allocating bits from the subnet identifier.
• fully specified static routeA fully specified route is a route that specifies both a next-hop IP address and an exit interface.
• link-local addressAn IPv6 link-local address is an IPv6 unicast address valid only for communication between devices on the same local network segment.
• network addressA network address is the first IPv4 address in a network, with all host bits set to zero, and cannot be assigned to a host.
• host portionA host bit is an IPv4 address bit belonging to the host portion rather than the network portion.
• TCPTransmission Control Protocol is a transport-layer protocol that provides reliable, connection-oriented delivery with mechanisms for detecting and recovering from lost data.
• inter-vlan routingInter-VLAN routing is the forwarding of traffic between subnets associated with different VLANs in a segmented local network.
• maximum host countThe maximum host count is the number of IPv4 addresses in a network that remain assignable after excluding the network and broadcast addresses.
• full stateAn OSPF full adjacency is a synchronized relationship in which neighboring routers have exchanged link-state information and synchronized their link-state databases.
• directly connected static routeA directly connected route is a route that specifies an exit interface without specifying a next-hop IP address.
• duplexDuplex is an interface transmission setting that specifies whether an Ethernet interface operates in full-duplex or half-duplex mode.
• root portRoot port selection is the spanning-tree procedure for choosing the port on a non-root bridge that provides its best path toward the root bridge.
• autonegotiationAutonegotiation is a link establishment technique in which connected interfaces automatically agree on compatible communication parameters such as speed and duplex.
• arp requestAn ARP request is a broadcast protocol message that asks the host using a specified IP address to provide its MAC address.
• port idA port ID is a unique STP identifier for a switch port, consisting of a port priority and a sequential port number.
• designated portA designated port is an STP port in the forwarding state that provides the preferred path away from the root bridge for a network segment.
• connected routeA connected route is a route to a network directly attached to an interface with an IP address that is operationally up.
• OSPF dead timerAn OSPF dead timer is the interval after which a neighbor is removed when no hello message has been received.
• IEEE 802.1QIEEE 802.1Q is the IEEE standard that defines VLAN tagging for Ethernet frames and carrying multiple VLANs over bridged links.
• network loopA Layer 2 loop is a cyclic forwarding path at the data-link layer that can cause frames to circulate repeatedly through switches.
• mac address tableA MAC address table is a switch data structure that maps learned MAC addresses to the ports through which their corresponding devices are reachable.
• arpARP is a protocol that resolves an IPv4 address to the MAC address of a host on the local network.
• three-way handshakeA three-way handshake is a three-message exchange used by TCP hosts to establish a connection before transmitting application data.
• link-state advertisementA link-state advertisement is a routing protocol data structure that describes a router's links and connected networks for distribution to other routers.
• port-channel interfaceA port-channel interface is a logical Cisco IOS interface representing an aggregated group of physical links.
• extended access control listAn extended access control list is an access control list that filters packets using multiple packet attributes, including Layer 4 protocols, source and destination IP addresses, and source and destination ports.
• routing tableA routing table is a data structure containing routes that describe reachable network destinations and how to forward packets toward them.
• headerAn IPv4 header is the network-layer protocol header that carries IPv4 addressing and control fields for delivering an IPv4 packet.
• local routeA local route is a route to the exact IP address configured on a router interface, represented with a /32 prefix.
• network switchA Layer 2 switch is a switch that forwards frames within a local network without performing network-layer routing.
• next hopA next hop is the adjacent router or forwarding address to which a packet is sent on its path toward a destination network.
• first hop redundancy protocolA first hop redundancy protocol is a protocol that provides a resilient default gateway by presenting end hosts with a virtual gateway backed by multiple routers.
• vlanA VLAN is a logically isolated local-area network created within a switched physical network.
• frameA frame is a data-link-layer protocol data unit consisting of a packet combined with a Layer 2 header and trailer.
• default gatewayA default gateway is the router or forwarding path used to send traffic toward destinations outside a device's known networks.
• root costRoot cost is the cumulative spanning-tree path cost from a switch through a port to the root bridge.
• OSPF neighbor relationshipAn OSPF adjacency is an established neighbor relationship between two OSPF routers that enables protocol database synchronization.
• privileged exec modePrivileged EXEC mode is the Cisco IOS CLI operational mode that provides access to configuration commands and advanced operational commands.
• OSPF hello messageAn OSPF hello message is an OSPF control message used to discover neighbors and maintain established neighbor relationships.
• network commandThe network command is a Cisco IOS routing-protocol configuration command that selects interfaces for protocol activation based on IP-address matching and a wildcard mask.
• router ospfrouter ospf is a Cisco IOS configuration command that creates or selects an OSPF process and enters OSPF router configuration mode.
• layer 3 switchA multilayer switch is a network switch that performs forwarding at multiple protocol layers, including the data link and network layers.
• eui-64 keywordAn EUI-64 interface identifier is a 64-bit IPv6 interface identifier derived using the Extended Unique Identifier format.
• floating static routeA floating static route is a static route configured with an administrative distance higher than the preferred route source so it can serve as a backup route.
• first usable addressThe first usable address is the first IPv4 address after the network address that can be assigned to a host.
• last usable addressThe last usable address is the IPv4 address immediately before the broadcast address that can be assigned to a host.
• administrative distanceAdministrative distance is a router metric that expresses the relative trustworthiness of a route source.
• recursive static routeA recursive static route is a static route that specifies a next-hop IP address and requires an additional lookup to determine the forwarding interface.
• no shutdown commandThe Cisco IOS no shutdown command removes the shutdown state from an interface and enables it.
• active routerAn active router is the router in a first hop redundancy group that currently forwards traffic for the shared default gateway.
• OSPF processAn OSPF process is a locally running instance of OSPF on a router that independently maintains routing information and calculates routes.
• OSPF backup designated routerAn OSPF backup designated router is the elected standby router that takes over the designated-router role if the DR is lost.
• OSPF broadcast network typeThe OSPF broadcast network type is an OSPF interface configuration for multi-access networks that supports dynamic neighbor discovery and designated-router and backup-designated-router election.
• OSPF designated routerAn OSPF designated router is the elected router that reduces adjacency and flooding overhead on a broadcast network segment.
• OSPF point-to-point network typeThe OSPF point-to-point network type describes a network segment connecting exactly two routers without designated-router election.
• VTPVTP synchronization is the process by which switches update their VLAN databases to match the latest database version advertised by another switch.
• arp replyAn ARP reply is a unicast protocol message that provides a host's MAC address to the host that sent an ARP request.
• most specific matching routeThe most specific matching route is the route whose network prefix has the greatest number of bits matching a packet's destination IP address.
• IPv4An IPv4 address is a 32-bit network-layer address used to identify a source or destination in IPv4 communication.
• virtual ip addressA virtual IP address is a shared logical IP address presented by a first-hop redundancy group as the default gateway for end hosts.
• UDPUser Datagram Protocol is a transport-layer protocol that sends datagrams without guaranteeing delivery of every message.
• virtual mac addressA virtual MAC address is a logical link-layer address associated with a virtual router or forwarding role rather than a single physical interface.
• network hopA hop is one journey of a message from one network node to the next node along its path to a destination.
• full duplexFull duplex is a communication mode in which an interface can transmit and receive simultaneously without collisions on the link.
• half duplexHalf duplex is a communication mode in which an interface cannot transmit and receive simultaneously and must wait for the medium to become available.
• csma/cdCSMA/CD is the Ethernet medium-access method in which devices detect carrier activity, transmit when the medium is available, and handle collisions.
• Open Shortest Path FirstOSPFv2 is the version of OSPF primarily used to route IPv4 networks.
• mac agingMAC address learning is the switch process of associating source MAC addresses with the ports or interfaces on which frames arrive.
• OSPF areaAn OSPF area is a logical subdivision of an OSPF autonomous system whose routers share a link-state database.
• binary representationBinary language is a computer representation system composed of sequences of 0s and 1s that encode data and computational information.
• bridge priorityBridge priority is the 16-bit priority component of a spanning-tree bridge identifier, combining a configurable value with the VLAN identifier.
• extended system idThe Extended System ID is the portion of a spanning-tree bridge priority that identifies the VLAN associated with the spanning-tree instance.
• dynamic etherchannelA dynamic EtherChannel is an EtherChannel configuration in which neighboring switches negotiate with each other using a protocol to form the logical link.
• ipv6 route commandThe Cisco IOS ipv6 route command creates a static IPv6 route in a router's routing table.
• CCNAThe CCNA exam is Cisco's associate-level certification examination for foundational networking knowledge and skills.
• vlan tagA VLAN tag is a four-byte 802.1Q field inserted into an Ethernet frame to identify its VLAN and carry related control information.
• local networkA local area network is a network that connects devices within a limited geographic area such as an office or building.
• acl sequence numberAn ACL sequence number is an ordering value assigned to an access control entry within an access control list.
• Dynamic Trunking ProtocolDTP negotiation is the exchange of Dynamic Trunking Protocol messages to agree on a switch-link operational mode.
• access portAn untagged port is a switch port that sends and receives Ethernet frames without VLAN tags.
• forwarding stateThe forwarding state is an STP port state in which a switch can learn MAC addresses and forward ordinary frames.
• wildcard maskA wildcard mask is a 32-bit bit mask in which zero bits require corresponding address bits to match and one bits ignore them during address matching.
• switch virtual interfaceA switch virtual interface is a virtual Layer 3 interface on a multilayer switch associated with a VLAN and configured with an IP address.
• interface configuration modeInterface configuration mode is a Cisco IOS command-line mode in which settings for a specific network interface can be configured.
• ip address commandThe ip address command is a Cisco IOS interface-configuration command that assigns an IPv4 address and netmask to an interface.
• lacpLACP is a link-aggregation control protocol that negotiates and maintains bundled network links between compatible devices.
• PAgPPAgP is Cisco's proprietary protocol for negotiating the formation of an EtherChannel between switch ports.
• Enhanced Interior Gateway Routing ProtocolEnhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco-developed interior gateway routing protocol with distance-vector characteristics and support for metric-based route selection.
• OSPF network typeAn OSPF network type is an interface setting that determines the OSPF communication behavior used on a connected network.
• vlan idA VLAN ID is the numeric identifier, represented in the 802.1Q VLAN Identifier field, that specifies the VLAN associated with an Ethernet frame.
• numbered access control listA numbered access control list is an access control list identified by a numeric identifier and traditionally configured from global configuration mode.
• spanning-tree instanceA spanning-tree instance is an independently running spanning-tree protocol instance associated with one VLAN or a group of VLANs.
• loopback interfaceA loopback interface is a virtual software-based router interface that remains operational while the device is operational unless administratively disabled.
• Neighbor Discovery ProtocolNDP is the IPv6 Neighbor Discovery Protocol, which provides mechanisms for discovering neighboring nodes and maintaining local-link reachability information.
• Hot Standby Router ProtocolHot Standby Router Protocol is a Cisco-developed first hop redundancy protocol that provides a virtual default gateway through coordinated routers.
• show interfaces trunkshow interfaces trunk is a Cisco IOS command that displays trunk-port status, encapsulation, and VLAN allowance information.
• command-line interfaceA command-line interface is a text-based interface through which a user controls and interacts with a device by entering commands.
• switchport access vlanswitchport access vlan is a Cisco IOS interface-configuration command that assigns an access port to a specified VLAN.
• ip routeip route is a Cisco IOS configuration command that creates a static route in a router's routing table.
• standby routerA standby router is an HSRP router that monitors the active router and is ready to assume packet forwarding if it fails.
• Dijkstra's algorithmDijkstra's algorithm is a shortest-path graph algorithm for calculating minimum-cost paths from a source node.
• non-designated portAn alternate port is an RSTP port that provides an alternate path toward the root bridge and can transition to forwarding if the root port fails.
• hubA hub is a network device that repeats incoming signals to multiple connected ports, causing attached devices to share a transmission medium.
• acknowledgment numberAn acknowledgment number is a TCP value identifying the next sequence number or byte the receiver expects.
• window size fieldThe window size field is a TCP-header field that advertises how much data the receiver can accept before requiring an acknowledgment.
• interface identifierAn interface identifier is the 64-bit host portion of an IPv6 address that identifies a network interface within an IPv6 prefix.
• arp tableAn ARP table is a host-maintained list that associates IP addresses with corresponding MAC addresses.
• switchingA forwarding decision is a router's selection of the next forwarding action for a packet based on its destination and routing information.
• OSPF DROtherAn OSPF DROther is a router on a broadcast segment that is neither the designated router nor the backup designated router.
• classful networkingClassful networking is an IPv4 addressing architecture based on the fixed network boundaries and default prefix lengths of address classes A, B, and C.
• HTTPSHTTPS is a protocol for transferring web resources over HTTP with protection provided by TLS.
• root bridge electionRoot bridge election is the spanning-tree procedure for selecting the bridge that serves as the reference point for the spanning-tree topology.
• switchport mode accessswitchport mode access is a Cisco IOS interface-configuration command that manually sets a switch port to access mode.
• maximum transmission unitMTU, or maximum transmission unit, is the largest packet size that an interface can forward without requiring fragmentation at that interface.
• channel-group commandThe channel-group command assigns a switch port to an EtherChannel and specifies its negotiation or static mode.
• show etherchannel summaryshow etherchannel summary is a Cisco IOS command that displays the status and member-port information of EtherChannels.
• collision domainA collision domain is a network segment in which simultaneous transmissions can interfere and cause collisions.
• user exec modeUser EXEC mode is the initial Cisco IOS command-line mode that provides limited operational access before privileged authorization.
• RSTP synchronization mechanismThe RSTP synchronization mechanism is a spanning-tree procedure that coordinates neighboring switch ports so eligible ports can transition rapidly to forwarding without waiting for spanning-tree timers.
• network packetA packet is a network-layer protocol data unit consisting of a segment combined with a Layer 3 header.
• PVST+PVST+ is Cisco's spanning-tree implementation that maintains a separate spanning-tree instance for each VLAN and supports ISL and 802.1Q trunk encapsulation.
• OSPF reference bandwidthOSPF reference bandwidth is the configured baseline bandwidth used to calculate interface costs.
• show ip interfaceshow ip interface is a Cisco IOS command that displays detailed IP configuration and operational information for interfaces.
• show ip interface briefshow ip interface brief is a Cisco IOS command that displays concise IPv4 addressing and operational status information for interfaces.
• OSPF neighbor stateAn OSPF neighbor state is a stage in the process by which two OSPF routers verify compatibility and establish a neighbor relationship.
• interface vlan commandinterface vlan is a Cisco IOS command that enters configuration mode for the switch virtual interface of a specified VLAN.
• no switchportno switchport is a Cisco IOS interface command that converts a multilayer-switch port from switching operation to routed operation.
• routed portA routed port is a physical multilayer-switch port configured to operate as a router interface rather than a Layer 2 switchport.
• interior gateway protocolAn interior gateway protocol is a routing protocol that exchanges reachability information within a single autonomous system.
• OSPF autonomous system border routerAn OSPF autonomous system border router connects an OSPF autonomous system to external networks or routing domains.
• fiber-optic cableA fiber-optic cable is a cable that transmits data as light through one or more glass or plastic optical fibers.
• duplex mismatchA duplex mismatch is a link condition in which two connected interfaces use different duplex settings or incompatible autonegotiation behavior.
• router on a stickRouter on a stick is an inter-VLAN routing method that uses one router interface with multiple VLAN-tagged virtual subinterfaces over a trunk link.
• proxy arpProxy ARP is a router feature that replies to an ARP request on behalf of another host and supplies the router's own MAC address.
• dotted decimal notationDotted decimal notation is the representation of a 32-bit IPv4 address as four decimal octets separated by periods.
• ip access-groupip access-group is a Cisco IOS interface-configuration command that applies an IP access control list in an inbound or outbound direction.
• allowed vlan listAn allowed VLAN is a VLAN permitted to traverse a trunk interface.
• solicited-node multicast addressA solicited-node multicast address is an IPv6 multicast address derived from the last six hexadecimal digits of a unicast address for targeting specific neighbors on a link.
• broadcast networkA broadcast domain is the set of network devices that receive a broadcast frame sent by a member of the set.
• ipv6 neighbor tableAn IPv6 neighbor table is a device-maintained database that maps IPv6 neighbor addresses to link-layer addresses and associated resolution state or interface information.
• neighbor solicitation messageA Neighbor Solicitation is an ICMPv6 Neighbor Discovery message used to request link-layer information or verify the reachability of a neighboring node.
• backup portA backup port is an RSTP port that provides a redundant path to the same network segment as a designated port on the same switch.
• ACK flagThe ACK flag is a TCP control bit indicating that the acknowledgment-number field is valid for acknowledging received data or control messages.
• FIN flagThe FIN flag is a TCP control bit used to signal that a host has finished sending data and is closing its direction of a connection.
• four-way handshakeA four-way handshake is the typical four-message TCP procedure for terminating a connection using FIN and ACK control flags.
• retransmission timeoutA retransmission timeout is the period a TCP sender waits for an acknowledgment before retransmitting an unacknowledged segment.
• SYN flagThe SYN flag is a TCP control flag used to initiate connection establishment and synchronize sequence numbers.
• default routeA default route is a route with destination prefix 0.0.0.0/0 that matches every IPv4 address when no more specific route matches.
• native vlan mismatchA native VLAN mismatch is a trunk-link misconfiguration in which the two connected ports assign different VLANs to untagged traffic.
• switchport trunk encapsulationswitchport trunk encapsulation is a Cisco IOS interface command that selects the encapsulation protocol for a trunk port.
• vlan hoppingVLAN hopping is unauthorized or unintended traffic crossing from one VLAN into another VLAN.
• ipv6 hextetAn IPv6 hextet is a group of 16 bits in an IPv6 address, conventionally represented by four hexadecimal digits.
• primary serverA VTP primary server is the single VTP version 3 server in a domain authorized to create, modify, and delete VLANs.
• ipv6 address commandThe ipv6 address command is a Cisco IOS interface-configuration command that assigns an IPv6 address, including a manually specified link-local address.
• octetAn octet is a group of exactly eight bits, especially one of the four 8-bit groups in an IPv4 address.
• OSI network modelThe OSI model is a seven-layer conceptual framework for describing the functions involved in network communication.
• router-id commandThe router-id command configures the router ID for a Cisco IOS OSPF process.
• backbone areaThe OSPF backbone area is area 0, the central area through which traffic between non-backbone areas passes.
• multi-area ospfMulti-area OSPF is an OSPF design that divides an autonomous system into multiple areas to limit database size and change propagation.
• OSPF area border routerAn OSPF area border router connects one or more nonbackbone areas to the backbone area.
• extended numbered aclAn extended numbered ACL is an extended access control list identified by a number from the extended ACL ranges.
• global configuration modeGlobal configuration mode is a Cisco IOS CLI mode in which device-wide settings and access to more specific configuration modes can be configured.
• distance-vector routing protocolDistance-vector routing calculates paths from route information received from neighboring routers rather than from a complete network topology map.
• link-state routing protocolLink-state routing builds a topology map of the network and calculates routes using that map.
• VTP off modeVTP off mode is a VTP operating mode in which a switch does not participate in VTP or forward VTP messages.
• EthernetEthernet is a family of wired networking standards defining physical connection characteristics and data formatting for network transmission.
• subinterfaceA subinterface is a logical router interface created from a physical interface and configured as an independent Layer 3 interface.
• administrative modeAn administrative mode is the configured switch-port mode that determines how the port negotiates or operates as an access or trunk port.
• operational modeAn operational mode is the mode in which a switch port is currently operating, such as access or trunk mode.
• borrowed bitA borrowed bit is a host bit reassigned to the network portion of an IPv4 address during subnetting.
• de-encapsulationDe-encapsulation is the process of inspecting and removing protocol headers and trailers as received data moves up a networking stack.
• ipv6 unicast-routing commandThe Cisco IOS ipv6 unicast-routing command enables IPv6 unicast packet forwarding between interfaces.
• learning stateThe learning state is an STP port state in which a port listens for BPDUs and learns MAC addresses but does not yet forward traffic.
• listening stateThe listening state is an STP transitional port state in which a switch port prepares for forwarding without learning MAC addresses or forwarding data frames.
• IEEE 802.1wRapid Spanning Tree Protocol is a faster-converging spanning-tree protocol that reduces the time required to transition ports after topology changes.
• data sequencingData sequencing is the process of assigning or using ordering information so received data can be restored to its transmission order.
• retransmissionTCP retransmission is the sending of a segment again after its acknowledgment is not received within the retransmission timeout or its integrity check fails.
• running-configThe running-config is the Cisco IOS configuration currently held in active device memory and used for operation.
• payloadA payload is the data carried inside a protocol data unit, excluding that unit's protocol control information.
• protocol data unitA protocol data unit is a unit of data consisting of a protocol payload together with the control information added at a networking layer.
• Cisco IOS command-line interfaceThe Cisco IOS command-line interface is the text-based interface through which users enter commands to configure and operate Cisco IOS devices.
• vlan commandvlan is a Cisco IOS configuration command that creates or selects a VLAN and enters VLAN configuration mode.
• unknown unicast frameAn unknown unicast frame is a unicast frame whose destination MAC address has no entry in the receiving switch's MAC address table.
• organizationally unique identifierAn organizationally unique identifier is the first three bytes of a MAC address, assigned by the IEEE to identify a manufacturer.
• 2-Way neighbor stateThe OSPF 2-Way neighbor state indicates that routers have established bidirectional communication without necessarily forming a full adjacency.
• classless networkingClassless networking is an IPv4 addressing system in which prefix lengths are not restricted by address class.
• VTP revision numberA VTP revision number is a version counter used to determine which VLAN database information should synchronize within a VTP domain.
• dynamic autoswitchport mode dynamic auto is a Cisco IOS command that configures a switch port to passively negotiate trunking with a neighboring port.
• networkA computer network is a set of interconnected devices that communicate and share resources.
• standard named aclA named access control list is an access control list identified by a name and configured through a dedicated ACL configuration mode.
• speed mismatchA speed mismatch is a condition in which two connected network interfaces are configured to communicate at different transmission speeds.
• DR/BDR electionA DR/BDR election is the OSPF selection process that chooses a designated router and backup designated router on a broadcast segment.
• dynamic neighbor discoveryDynamic neighbor discovery is the automatic identification of connected routing neighbors through protocol messages rather than manually configured neighbor addresses.
• OSPF interface priorityOSPF interface priority is a configurable value used to influence a router's eligibility and rank in designated-router elections.
• deny-by-defaultAn implicit deny is a hidden access-control rule that denies traffic matching none of an access control list's explicit conditions.
• frame floodingFrame flooding is the forwarding of a frame out multiple switch ports when its destination is unknown or requires broadcast delivery.
• router advertisementA Router Advertisement is an ICMPv6 message that a router sends to announce itself and provide local network configuration information.
• router solicitationA Router Solicitation is an ICMPv6 message that asks local routers to identify themselves and provide configuration information.
• 8P8C connectorRJ45 is the commonly used name for the modular connector used with Ethernet twisted-pair cabling.
• routing table populationRouting table population is the process of selecting which learned or configured routes a router enters into its routing table.
• ipv4 address exhaustionIPv4 address exhaustion is the depletion of globally usable IPv4 addresses caused by demand exceeding the available 32-bit address space.
• class bClass B is an IPv4 address class whose first octet ranges from 128 through 191 and whose default network prefix length is /16.
• unique local addressA unique local address is an IPv6 private unicast address intended for use within internal networks and not for communication over the public internet.
• enable secretThe enable secret command is a Cisco IOS global-configuration command that sets the password for privileged EXEC mode.
• BPDU GuardBPDU Guard is a switch-port protection feature that places a port into an error-disabled state when the port receives a Bridge Protocol Data Unit.
• router discoveryRouter discovery is the process by which an IPv6 host learns about available routers and related network configuration information.
• global unicast addressA global unicast address is an IPv6 unicast address that is globally unique and routable over the internet.
• interface commandThe Cisco IOS interface command enters interface configuration mode for the specified interface.
• passive OSPF interfaceA passive OSPF interface participates in OSPF but does not send hello messages to form neighbor relationships.
• ipv6 headerAn IPv6 header is the fixed 40-byte network-layer protocol header that carries IPv6 packet control and addressing information.
• exit interfaceAn exit interface is the router interface through which a packet is forwarded toward its destination.
• session multiplexingSession multiplexing is the process of tracking multiple communication sessions concurrently by distinguishing them with transport-layer identifiers such as port numbers.
• HSRP groupAn HSRP group is a set of HSRP-configured routers that share a virtual IP address and elect active and standby roles.
• anycastAn anycast address is an IP address configured on multiple hosts so that traffic sent to it reaches one host selected according to network routing.
• broadcast stormA broadcast storm is an excessive volume of broadcast or similar replicated traffic that consumes network resources and can make a network unusable.
• connection establishmentTCP connection establishment is the process of creating a TCP connection before application data is exchanged.
• sequence number fieldThe sequence number field is a TCP-header field that identifies the position of transmitted data in a byte stream.
• tcp checksum fieldThe TCP checksum field is a TCP-header field containing a calculated value used to detect corruption in a TCP segment.
• tcp connection terminationTCP connection termination is the process of closing a TCP connection after the necessary data has been exchanged.
• tcp flags fieldThe TCP flags field is an eight-bit TCP-header field whose individual bits indicate or control protocol behaviors.
• tcp headerA TCP header is the transport-layer header containing control, addressing, sequencing, acknowledgment, checksum, and flow-control fields for a TCP segment.
• HSRP hello messageA hello message is a periodically transmitted control message used by first hop redundancy routers to establish and maintain neighbor relationships.
• context-sensitive helpContext-sensitive help is an interactive CLI feature that presents commands, keywords, and completions valid at the current input position.
• ip routing commandip routing is a Cisco IOS global-configuration command that enables Layer 3 packet forwarding on a multilayer switch.
• up/up interface stateAn up/up interface state indicates that a network interface is administratively enabled and its underlying protocol is operational.
• destination address fieldAn IPv6 destination address field is a 128-bit IPv6 header field containing the destination IPv6 address of the packet.
• source address fieldAn IPv6 source address field is a 128-bit IPv6 header field containing the source IPv6 address of the packet.
• icmpv6ICMPv6 is the IPv6-specific version of the Internet Control Message Protocol for communicating control, error, and diagnostic information.
• neighbor advertisementA Neighbor Advertisement is an ICMPv6 message that communicates a neighbor's link-layer address or indicates that an IPv6 address is already in use.
• named acl config modeNamed ACL config mode is a Cisco IOS configuration mode in which individual access control entries are added or edited for an access control list.
• vlan databaseA VLAN database is a switch-maintained record of configured VLANs and the ports assigned to them.
• duplicate address detectionDuplicate address detection is the process of determining whether an IPv6 address is already in use on a link before assigning it to an interface.
• unicast frameUnicast is one-to-one network communication directed from one sender to one destination.
• show vlan briefshow vlan brief is a Cisco IOS command that displays configured VLANs, their status, and their assigned switch ports.
• extended named aclAn extended named ACL is an extended access control list identified by a name.
• dynamic desirableswitchport mode dynamic desirable is a Cisco IOS command that configures a switch port to actively negotiate trunking with a neighboring port.
• autonomous systemAn autonomous system is a collection of networks and routers under a common administrative control that participates in interdomain routing.
• exterior gateway protocolAn exterior gateway protocol is a routing protocol that exchanges routing information between different autonomous systems.
• variable-length subnet maskingVariable-length subnet masking is a subnetting method that divides an address block into subnets of different sizes based on address requirements.
• interface descriptiondescription is a Cisco IOS interface-configuration command that assigns descriptive text to an interface.
• point-to-point communicationAn RSTP point-to-point link is a full-duplex link whose connected ports can use the RSTP synchronization mechanism to transition rapidly to forwarding.
• enableThe Cisco IOS enable command changes the session from user EXEC mode to privileged EXEC mode, subject to authorization.
• hexadecimal numberThe hexadecimal number system is a base-16 positional numeral system using the digits 0 through 9 and the letters A through F.
• HSRP version 2HSRP version 2 is the second version of the Hot Standby Router Protocol for providing a redundant virtual default gateway.
• Cisco Packet TracerCisco Packet Tracer is Cisco network simulation software for modeling and practicing the configuration of network devices and networks.
• PortFastThe spanning-tree portfast command is a Cisco IOS interface-configuration command that enables PortFast on a switch port.
• BUM trafficBUM traffic is broadcast, unknown-unicast, and multicast frame traffic that switches may replicate across multiple ports.
• lsa floodingLSA flooding is the process of distributing link-state advertisements to all routers within an OSPF area.
• BPDU filterBPDU Filter is a spanning-tree feature that suppresses the sending or processing of Bridge Protocol Data Units on a switch port.
• extended-range vlanAn extended-range VLAN is a VLAN numbered from 1006 through 4094 in Cisco switch VLAN classification.
• loop guardLoop Guard is a spanning-tree protection feature that places a port into a loop-inconsistent state when expected BPDUs stop arriving, preventing erroneous transition to forwarding.
• type 1 lsaA Type 1 LSA is an OSPF router advertisement generated by every router to describe that router's links.
• type 2 lsaA Type 2 LSA is an OSPF network advertisement generated by the designated router for a broadcast network to list the routers on the segment.
• type 5 lsaA Type 5 LSA is an OSPF autonomous-system-external advertisement generated by an autonomous system boundary router to advertise routes to external networks.
• ipv4 fragmentation fieldsThe IPv4 fragment offset field is a 13-bit header field that indicates a fragment's position within its original packet.
• binary-to-decimal conversionBinary-to-decimal conversion is the process of calculating a decimal value by summing the positional values of the set bits in a binary number.
• decimal-to-binary conversionDecimal-to-binary conversion is the process of representing a decimal value as a sequence of binary digits using positional subtraction or addition.
• root guardRoot Guard is a spanning-tree protection feature that prevents a port from accepting a superior BPDU and thereby prevents an external switch from becoming the root bridge.
• broadcast frameBroadcast is one-to-all network communication directed to every host on the relevant network segment.
• router configuration modeRouter configuration mode is a Cisco IOS CLI state in which routing-protocol configuration commands can be entered for a router process.
• known unicast frameA known unicast frame is a unicast frame whose destination MAC address has an entry in the receiving switch's MAC address table.
• information flowA flow is a communication between two network nodes whose traffic can be assigned consistently to a physical link.
• adjacent-layer interactionAn adjacent-layer interaction is communication in which one layer of the TCP/IP model provides a service to the layer directly above it on the same computer.
• same-layer interactionA same-layer interaction is communication between corresponding layers of the TCP/IP model on different computers.
• edge linkAn RSTP edge link is a link connecting a switch port to an end host, allowing the port to transition immediately to forwarding without posing a Layer 2 loop risk.
• reloadThe Cisco IOS reload command restarts a network device.
• shared linkAn RSTP shared link is a half-duplex link whose ports cannot use the RSTP synchronization mechanism and transition like standard STP ports.
• configuration modeA configuration mode is a Cisco IOS CLI state that permits configuration commands for the device or a specific feature.
• enable passwordThe enable password command is a Cisco IOS global-configuration command that configures the password for privileged EXEC access.
• stateless address autoconfigurationStateless Address Autoconfiguration is an IPv6 mechanism by which a host generates its own address and obtains network configuration without a centralized address-assignment server.
• routerA network device that forwards packets between different networks based on network-layer addressing.
• console portA console port is a physical device port that provides a direct local connection for configuring a device through its command-line interface.
• exec modeAn EXEC mode is a Cisco IOS command-line operating mode that determines which commands are available and whether device operations can be performed.
• networking modelA networking model is a framework that organizes the functions required for data to travel from a source to a destination over a network.
• Auto MDI-XAuto MDI-X is an Ethernet interface feature that automatically adjusts transmit and receive pin assignments to match the connected device.
• trailerAn Ethernet trailer is supplemental data placed at the end of an Ethernet frame, including the FCS field for error detection.
• encapsulation dot1qencapsulation dot1q is a Cisco IOS interface command that associates a router subinterface with an IEEE 802.1Q VLAN and optionally marks it as native.
• show interfaces statusshow interfaces status is a Cisco IOS switch command that displays interface status, descriptions, speed, and duplex information.
• external routeAn external route is a route to a destination outside the OSPF autonomous system that is advertised by an ASBR.
• inter-area routeAn inter-area route reaches a destination in an OSPF area other than one to which the router is directly connected.
• intra-area routeAn intra-area route reaches a destination within an OSPF area to which the router is connected.
• BGPBGP is an exterior gateway routing protocol that calculates routes between autonomous systems using path-vector information.
• active modeActive mode is an LACP setting that actively attempts to negotiate an EtherChannel with a neighboring switch.
• auto modeAuto mode is a PAgP setting that passively responds to negotiation messages from a desirable-mode neighbor.
• desirable modeDesirable mode is a PAgP setting that actively attempts to negotiate an EtherChannel with a neighboring switch.
• ipv4 networkAn IPv4 address block is a contiguous range of IPv4 addresses represented by a common network prefix.
• passive modePassive mode is an LACP setting that responds to negotiation messages from an active-mode neighbor without initiating negotiation.
• twisted pairA twisted pair is a cable construction in which two conductors are helically twisted together to reduce electromagnetic interference.
• configure terminal commandThe configure terminal command is a Cisco IOS CLI command that enters global configuration mode from privileged EXEC mode.
• class cClass C is an IPv4 address class whose first octet ranges from 192 through 223 and whose default network prefix length is /24.
• ipv4 address classClass A is an IPv4 address class whose first octet ranges from 0 through 127 and whose default network prefix length is /8.
• network segmentationNetwork segmentation is the division of a network into separate logical or physical segments to limit the scope of communication.
• startup-configThe startup-config is the Cisco IOS configuration file stored in nonvolatile memory and loaded when a device boots.
• copy running-config startup-configThe Cisco IOS write memory command saves the active configuration to startup-config.
• fixed-length subnet maskingFixed-length subnet masking is a subnetting technique that divides an address space into subnets of the same size.
• address blockAn address block is a contiguous range of IP addresses that can represent a network or be divided into smaller subnetworks.
• VTP domainA VTP domain is a group of switches in a LAN that share the same VTP domain name and VLAN configuration information.
• Gateway Load Balancing ProtocolGateway Load Balancing Protocol is a Cisco first hop redundancy protocol that provides gateway redundancy while distributing traffic across multiple routers.
• OSPF message typeAn OSPF message type is one of the protocol messages used for neighbor discovery, link-state database synchronization, or acknowledgment.
• ephemeral portAn ephemeral port is a port numbered from 49152 through 65535 that is commonly used as a client source port and does not require registration.
• registered portA registered port is a port numbered from 1024 through 49151 that protocols may register with IANA to reduce conflicts.
• well-known portA well-known port is a port numbered from 0 through 1023 that is reserved for common protocols and assigned under strict control.
• switchport nonegotiateswitchport nonegotiate is a Cisco IOS interface command that prevents a switch port from sending Dynamic Trunking Protocol messages.
• VTP client modeVTP client mode is a VTP operating mode in which a switch cannot modify VLANs but receives and synchronizes VLAN database advertisements.
• VTP modeA VTP mode is a switch operating role that determines how the switch creates, synchronizes, forwards, or ignores VTP information.
• VTP server modeVTP server mode is a VTP operating mode in which a switch can create, modify, and delete VLANs and advertise those changes to other switches in the VTP domain.
• VTP transparent modeVTP transparent mode is a VTP operating mode in which a switch maintains an independent VLAN database, does not synchronize it, and forwards VTP messages.
• spanning-tree mode commandThe spanning-tree mode command is a Cisco IOS global-configuration command that selects the spanning-tree mode used by a switch.
• link-state update messageA link-state update message is an OSPF protocol message that carries one or more link-state advertisements.
• interface rangeinterface range is a Cisco IOS interface-configuration command that selects multiple interfaces for simultaneous configuration.
• quality of serviceQuality of Service is the classification and prioritization of network traffic to provide differentiated service levels.
• time to liveTime to live is an 8-bit IPv4 packet-header field whose value limits the number of router hops a packet may traverse before being discarded.
• ospfv3OSPFv3 is the version of OSPF primarily used to route IPv6 networks and capable of supporting IPv4 as well.
• ICMPICMP, or Internet Control Message Protocol, is a network-layer control protocol that communicates delivery status and diagnostic information for Internet Protocol.
• pingPing is a network utility that tests host reachability by sending Internet Control Message Protocol echo requests and receiving echo replies.
• Virtual Router Redundancy ProtocolVirtual Router Redundancy Protocol is a standards-based first hop redundancy protocol that provides a virtual default gateway through coordinated routers.
• 1000BASE-T1000BASE-T is an Ethernet physical-layer standard that transmits 1 Gbps over four twisted-pair wire pairs.
• 100BASE-T100BASE-T is an Ethernet physical-layer standard that transmits 100 Mbps over two twisted-pair wire pairs.
• 10BASE-T10BASE-T is an Ethernet physical-layer standard that transmits 10 Mbps over two twisted-pair wire pairs.
• 10GBASE-T10GBASE-T is an Ethernet physical-layer standard that transmits 10 Gbps over four twisted-pair wire pairs.
• forward delay timerA forward delay timer is an STP timing parameter that determines how long a port remains in the listening and learning states before forwarding frames.
• max age timerA max age timer is an STP timing parameter that specifies how long a switch waits without receiving BPDUs before recalculating the spanning-tree topology.
• decimal numeral systemThe decimal number system is a base-10 positional numeral system that uses the digits 0 through 9.
• static etherchannelA static EtherChannel is an EtherChannel configuration that forms a logical link from specified ports without negotiating with the neighboring device.
• EtherTypeEtherType is the Ethernet frame field designation for a Type/Length field value that identifies the encapsulated protocol or packet type.
• show ipv6 interface briefshow ipv6 interface brief is a Cisco IOS command that displays concise IPv6 addressing and operational status information for interfaces.
• frame check sequenceAn FCS, or Frame Check Sequence, is an Ethernet trailer field used to detect errors in an entire frame.
• console cableA console cable is a cable that connects a computer to a network device's console port for local management access.
• port-channel load-balanceport-channel load-balance is a Cisco IOS global configuration command that configures the traffic fields used to select EtherChannel member links.
• auto-cost reference-bandwidthauto-cost reference-bandwidth is a Cisco IOS OSPF router-configuration command that sets the reference bandwidth used for automatic cost calculation.
• bandwidth commandbandwidth kbps is a Cisco IOS interface-configuration command that sets the configured interface bandwidth in kilobits per second.
• ip ospf costip ospf cost is a Cisco IOS interface-configuration command that directly assigns an OSPF cost to an interface.
• show ip ospf interface briefshow ip ospf interface brief is a Cisco IOS command that displays concise OSPF information for router interfaces, including their costs.
• shutdownshutdown is a Cisco IOS interface configuration command that administratively disables an interface.
• show ip routeshow ip route is a Cisco IOS command that displays a router's IP routing table.
• bitA bit is the smallest unit of digital information and has one of two possible values, conventionally 0 or 1.
• bit per secondA bit per second is a unit of data transmission rate representing one transmitted bit per second.
• preambleA preamble is an Ethernet synchronization sequence transmitted before a frame to allow the receiver to prepare for incoming data.
• start frame delimiterA Start Frame Delimiter is an Ethernet byte pattern that marks the end of the preamble and the beginning of a frame.
• active virtual forwarderAn active virtual forwarder is a GLBP router role associated with a unique virtual MAC address that forwards traffic for the shared gateway.
• active virtual gatewayAn active virtual gateway is the GLBP router that assigns active virtual forwarders and answers address-resolution requests for the virtual gateway.
• show ip ospf neighborshow ip ospf neighbor is a Cisco IOS command that displays information about OSPF neighbor relationships.
• virtual switchA virtual switch is a logically defined switching instance that operates as an independent switch within shared physical switching hardware.
• failoverFailover is the transfer of an active network service or role to a standby device after the active device fails.
• gratuitous arpGratuitous ARP is an ARP reply sent without a preceding ARP request, typically to announce or refresh an address-to-MAC mapping.
• vtp primaryvtp primary is a Cisco IOS privileged EXEC command that designates a VTP server as the primary server for its domain.
• passive-interface default commandThe passive-interface command configures a specified OSPF-enabled interface to avoid sending OSPF messages for neighbor formation.
• show access-listsshow ip access-lists is a Cisco IOS command that displays configured IP access control lists.
• multimode fiberMultimode fiber is optical fiber that carries multiple propagation modes and is generally used for shorter-distance links.
• single-mode fiberSingle-mode fiber is optical fiber designed to carry a single propagation mode over relatively long distances with low dispersion.
• designated port selectionDesignated port selection is the spanning-tree procedure for choosing the forwarding port for each network segment.
• QUICQUIC is a transport-layer protocol built on UDP that provides TCP-like functionality with reduced latency and built-in encryption.
• real-time systemA real-time application is an application in which timely delivery of current data is more important than perfect delivery of all data.
• Trivial File Transfer ProtocolTrivial File Transfer Protocol is a simple file-transfer protocol that provides its own acknowledgment-based reliability while using UDP.
• stp port roleAn STP port role is a spanning-tree assignment that determines how a switch port participates in the loop-free topology.
• HSRP version 1HSRP version 1 is the first HSRP protocol version, using multicast address 224.0.0.2 and a two-hex-digit virtual MAC group identifier.
• dynamic mac addressA dynamic MAC address is a MAC address learned automatically by a switch from received frame source information.
• destination fieldA destination field is an Ethernet frame field that carries the MAC address of the intended next-hop recipient.
• source fieldA source field is an Ethernet frame field that carries the MAC address of the sending port.
• network interfaceA network interface is a connection point through which a device communicates with other devices in a network.
• usable address rangeA usable address range is the consecutive set of host-assignable IPv4 addresses between a network's first and last usable addresses.
• network bandwidthBandwidth is the total data-carrying capacity of a network connection, measured as the number of bits transferable per second.
• classless inter-domain routingCIDR notation is slash notation that expresses an IP address's network prefix length.
• link costA link cost is the OSPF cost associated with traversing a network link in route calculations.
• default-information originate commandThe default-information originate command is a Cisco IOS OSPF configuration command that causes an OSPF router to advertise a default route.
• spanning-tree link-type commandThe spanning-tree link-type point-to-point command is a Cisco IOS interface-configuration command that manually configures a port's RSTP link type as point-to-point.
• backbone routerA backbone router is an OSPF router with at least one interface in the backbone area.
• internal routerAn internal OSPF router is a router whose OSPF-enabled interfaces all belong to the same area.
• acl port operatorAn ACL port operator is a Cisco IOS access-control-list argument that specifies a relational test or interval for matching transport-layer port numbers.
• designated bridgeA designated bridge is the switch that has the designated port for a particular network segment.

These guides are generated from the text of Manning books by Manning's knowledge graph and link to the sections they draw on. The full books are available on liveBook and at manning.com.