Field notes / 006

Networking Glossary

Every term the labs use, defined in plain language, with a link to the explorer where you can see it working. Search or filter by topic — nothing leaves your browser.

102 terms

A

AdjacencyOSPF: A fully synchronized relationship between two OSPF neighbors. Only adjacent routers exchange link-state databases.Single area
Administrative distanceOSPF: A router's preference ranking between routing sources when more than one offers the same prefix. Lower distance is trusted first.Cost & SPF
Antenna gainRF & Wireless: How much an antenna concentrates energy in a chosen direction rather than adding power. Gain trades coverage width for reach.RF Math Explorer
AreaOSPF: A grouping of OSPF routers that share one link-state database. Areas limit flooding and shrink the shortest-path calculation.Multi-area design
Area Border RouterABROSPF: A router with interfaces in two or more areas. It summarizes prefixes between them and keeps a database per area.Multi-area design
Autonomous systemASGeneral: A network under one routing administration, identified by an AS number. Interior protocols run inside; BGP runs between.OSPF ↔ BGP redistribution
Autonomous System Boundary RouterASBROSPF: A router that injects routes learned from another protocol — BGP, static, EIGRP — into OSPF as external routes.OSPF ↔ BGP redistribution

B

Backbone area (Area 0)OSPF: The transit area every other area must connect to. Inter-area traffic passes through Area 0 by design.Multi-area design
Binary (base 2)Number Bases: Numbers built from only 0 and 1. Every masking, matching and addressing decision in networking happens at this level.Convert and see the bits
BitNumber Bases: A single binary digit — one 0 or one 1. The smallest unit of information.Number Bases
Bitwise ANDNumber Bases: The operation that combines an address with its mask to produce the network address: a bit survives only if both inputs are 1.Subnetting Lab
Blocked portSpanning Tree: A port intentionally left non-forwarding so the redundant link it belongs to cannot create a loop. It still listens, ready to take over.Find the dark cable
Border Gateway ProtocolBGPOSPF: The path-vector protocol that routes between autonomous systems on the internet. It chooses on policy attributes rather than a single cost metric.OSPF ↔ BGP redistribution
Bridge IDBIDSpanning Tree: The value switches compare during the root election: bridge priority first, then MAC address as the tiebreaker. Lowest wins.Spanning Tree Explorer
Bridge prioritySpanning Tree: A configurable number (default 32768, adjustable in steps of 4096) that lets you decide which switch becomes root instead of leaving it to MAC addresses.Drag a priority and watch the tree change
Bridge Protocol Data UnitBPDUSpanning Tree: The small frame switches exchange to advertise bridge IDs and path costs. BPDUs drive the election and detect topology changes.Spanning Tree Explorer
Broadcast addressAddressing & Subnetting: The last address in a subnet, with all host bits set to one. Traffic sent to it reaches every host on that subnet.Subnetting Lab
Broadcast domainGeneral: The set of devices a broadcast frame reaches — one VLAN or subnet. Routers separate broadcast domains.
Broadcast stormSpanning Tree: Broadcast frames circling a Layer 2 loop endlessly, multiplying until the network saturates. The problem spanning tree exists to prevent.Spanning Tree Explorer
Byte / octetNumber Bases: Eight bits, holding a value from 0 to 255. 'Octet' is the networking term used for each part of an IPv4 address.See octet breakdowns

C

Cable and connector lossRF & Wireless: Power lost between radio and antenna. It scales with cable length, cable type and frequency, and every connector adds a little more.Build a gain/loss chain
Classless Inter-Domain RoutingAddressing & Subnetting: The addressing model that replaced fixed Class A/B/C boundaries with arbitrary prefix lengths.Subnetting Lab
ConvergenceSpanning Tree: The period after a change during which every device recalculates and settles on a consistent view of the topology. Traffic may be disrupted until it completes.Fail a link and watch it settle

D

dBiRF & Wireless: Antenna gain compared with a theoretical isotropic radiator. Higher dBi means a narrower, more focused pattern.RF Math Explorer
dBmRF & Wireless: Absolute power referenced to one milliwatt. 0 dBm is 1 mW, 20 dBm is 100 mW, and every 3 dB roughly doubles or halves power.Convert dBm to milliwatts
DecibeldBRF & Wireless: A logarithmic ratio between two power levels. Gains and losses in dB simply add and subtract, which is why RF math uses them.RF Math Explorer
Decimal (base 10)Number Bases: Everyday base-10 numbers. Used for the human-readable octets in dotted-decimal IPv4 addresses.Number Bases
Default gatewayAddressing & Subnetting: The router address a host sends traffic to when the destination is outside its own subnet.
Designated portSpanning Tree: The forwarding port on each network segment — the port closest to the root on that segment. Every segment has exactly one.See port roles on the topology
Designated RouterDROSPF: On a multi-access segment, the router elected to represent the segment and reduce the number of adjacencies needed. The BDR is its standby.Single area

E

Effective Isotropic Radiated PowerEIRPRF & Wireless: Transmit power plus antenna gain minus cable and connector losses — the number regulators cap.Build a gain/loss chain
Equal-cost multipathECMPOSPF: Installing several paths of identical cost for one destination and load-sharing traffic across them.Cost & SPF

F

Fade marginRF & Wireless: Received level minus receiver sensitivity — the headroom protecting the link against rain, multipath and interference. Aim for 15–20 dB.Check your fade margin
Free-space path lossFSPLRF & Wireless: The signal loss from spreading over distance in clear space. It grows with both distance and frequency: 32.44 + 20log(km) + 20log(MHz).Calculate path loss
Frequency bandRF & Wireless: The slice of spectrum a link uses. 2.4 GHz travels further but is crowded; 5 and 6 GHz offer more channels with more path loss.Compare bands in the planner
Fresnel zoneRF & Wireless: The ellipse around the line of sight where obstructions cause interference. Keeping about 60% of the first zone clear is the usual target.Check Fresnel clearance

H

Hello / dead intervalOSPF: How often OSPF hellos are sent and how long silence is tolerated before a neighbor is declared down. Both must match between neighbors.Single area
Hexadecimal (base 16)hexNumber Bases: Base-16 digits 0–9 and A–F, where one digit is exactly four bits. Used for MAC addresses, IPv6, and protocol header dumps.Convert hex to binary

I

Interior vs exterior gateway protocolIGP / EGPGeneral: IGPs like OSPF find best paths inside one autonomous system; EGPs like BGP exchange reachability between autonomous systems.OSPF Explorer
IPv4 addressAddressing & Subnetting: A 32-bit host identifier written as four decimal octets, such as 192.168.10.25. Part of it identifies the network and part the host.Subnetting Lab
IPv6 addressAddressing & Subnetting: A 128-bit address written as eight hex groups, with runs of zeros compressed to '::'. /64 is the usual subnet size.Expand an IPv6 address

J

JitterGeneral: Variation in packet-to-packet delay. Even with low average latency, high jitter breaks up voice and video and causes buffer underruns.Link quality estimator

L

LatencyGeneral: The time a packet takes to travel from sender to receiver. Lower is better for interactive use; bulk transfer tolerates more.Link quality estimator
Layer 2 vs Layer 3General: Layer 2 switches frames within a broadcast domain using MAC addresses; Layer 3 routers forward packets between networks using IP addresses.
Line of sightLoSRF & Wireless: A clear straight path between antennas. Radio needs Fresnel clearance too, not just a visually unobstructed view.Link planner
Link aggregationLAGSpanning Tree: Bundling several physical links into one logical link so all of them forward traffic. Spanning tree sees a single port, so no cable is blocked.Switch to loop-free mode
Link budgetRF & Wireless: The full accounting from transmitter to receiver: power, gains, losses and path loss, ending in the expected received level.RF Math Explorer
Link-state advertisementLSAOSPF: One record in the link-state database describing a router, a network, a summary, or an external route. LSA types determine how far the record travels.LSA types 1–7
Link-state databaseLSDBOSPF: The collection of link-state advertisements a router has received. Within one area every router's database should be identical.Single area
Link-state vs distance-vectorOSPF: Link-state protocols share a map and each router computes paths itself; distance-vector protocols share their conclusions and trust neighbors' totals.OSPF Explorer
Longest prefix matchAddressing & Subnetting: The forwarding rule: when several routes match a destination, the most specific (longest) prefix is used.Subnetting Lab
Loopback addressAddressing & Subnetting: An address that always refers to the device itself — 127.0.0.1 in IPv4, ::1 in IPv6. Also a stable virtual interface on routers.
LSA Type 1 (Router LSA)OSPF: Generated by every router to describe its own interfaces and costs. Flooded only within its own area.LSA types 1–7
LSA Type 2 (Network LSA)OSPF: Generated by the designated router on a multi-access segment to list which routers are attached to it. Area-local.LSA types 1–7
LSA Type 3 (Summary LSA)OSPF: Generated by an area border router to advertise prefixes from one area into another, without the internal topology detail.LSA types 1–7
LSA Type 4 (ASBR Summary)OSPF: Tells routers in other areas how to reach the autonomous system boundary router that injected external routes.LSA types 1–7
LSA Type 5 (External LSA)OSPF: Describes a route redistributed from outside OSPF. Flooded through the whole domain except stub-type areas.LSA types 1–7
LSA Type 7 (NSSA External)OSPF: An external route injected inside a not-so-stubby area. The area border router converts it to a Type 5 on the way out.LSA types 1–7

M

MAC addressNumber Bases: A 48-bit Layer 2 hardware address in hex, split into a vendor prefix (OUI) and a device-specific half.Break down a MAC address
Maximum Transmission UnitMTUGeneral: The largest packet size a link carries without fragmenting. Mismatched MTUs cause hard-to-spot failures.
MetricGeneral: The number a routing protocol uses to rank paths. Each protocol defines its own, so metrics are not comparable across protocols.Cost & SPF
Most / least significant bitMSB / LSBNumber Bases: The leftmost bit carries the largest place value (128 in an octet); the rightmost carries the smallest (1).Number Bases
MultipathRF & Wireless: Copies of the same signal arriving via reflections at slightly different times, which can reinforce or cancel the direct signal.RF Math Explorer

N

Network addressAddressing & Subnetting: The first address in a subnet, with all host bits zero. It names the subnet and is not assigned to a host.Subnetting Lab
Network Address TranslationNATAddressing & Subnetting: Rewriting addresses (and often ports) at a boundary so many private hosts can share public addresses.
Next hopGeneral: The neighboring router a packet is handed to on its way to the destination.
NibbleNumber Bases: Four bits — exactly one hexadecimal digit. Handy when reading hex as binary.Number Bases
Noise floorRF & Wireless: The background RF energy present regardless of your signal. A high noise floor eats into usable margin.RF Math Explorer
Not-so-stubby areaNSSAOSPF: A stub area that is still allowed to originate its own external routes, carried as Type 7 LSAs.LSA types 1–7

O

Octal (base 8)Number Bases: Base-8 numbers, where one digit is three bits. Mostly seen in file permissions rather than addressing.Number Bases
Open Shortest Path FirstOSPFOSPF: A link-state interior routing protocol. Every router floods a description of its own links, builds an identical map of the area, and runs Dijkstra to pick shortest paths.OSPF Explorer
Organizationally Unique IdentifierOUINumber Bases: The first 24 bits of a MAC address, assigned to a manufacturer. Useful for identifying who made a device.Break down a MAC address
OSI modelGeneral: A seven-layer reference model, from physical cabling up to applications. Handy for placing where a protocol or problem lives.
OSPF costOSPF: The metric OSPF adds up along a path — traditionally reference bandwidth divided by interface bandwidth. Lower total cost wins.Cost & SPF

P

Packet lossGeneral: The fraction of packets that never arrive. A small percentage compounds quickly through retransmissions and codec concealment.Link quality estimator
Parabolic dish gainRF & Wireless: Approximate gain from dish diameter, frequency and aperture efficiency — bigger dishes and higher frequencies give more gain.Estimate dish gain
Path costSpanning Tree: The accumulated cost of the links between a switch and the root bridge. Faster links cost less, so the cheapest total path is chosen.Spanning Tree Explorer
Place valueNumber Bases: The weight of each digit position: 128 64 32 16 8 4 2 1 across an octet. Converting is just adding the weights that are set.Number Bases
Port numberNumber Bases: A 16-bit value (0–65535) identifying a service or session endpoint, often quoted in hex when reading packet captures.Number Bases
Prefix length / CIDR notationCIDRAddressing & Subnetting: Shorthand for the mask, written as a slash and the count of network bits: 10.0.0.0/24 means 24 network bits and 8 host bits.Subnetting Lab
Private address spaceAddressing & Subnetting: Ranges reserved for internal use — 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 — that are not routed on the public internet.Subnetting Lab

R

Rapid Spanning Tree ProtocolRSTPSpanning Tree: The faster successor to classic STP (802.1w). It reconverges in a second or two by negotiating with neighbors instead of waiting out fixed timers.Watch a link fail and reconverge
Received signal levelRSSIRF & Wireless: The power arriving at the receiver, in dBm: EIRP plus receive antenna gain minus path loss and receive-side losses.Link planner
Receiver sensitivityRF & Wireless: The weakest signal a radio can still decode at a given data rate. Faster rates need stronger signals.Link planner
RedistributionOSPF: Importing routes from one routing protocol into another. Metrics do not translate directly, so the imported cost must be chosen deliberately.OSPF ↔ BGP redistribution
Root bridgeSpanning Tree: The single switch elected as the reference point of the tree. Every other switch calculates its best path toward the root, and all of the root's ports forward.Change priorities and re-elect the root
Root portSpanning Tree: The one port on a non-root switch with the lowest cost path toward the root bridge. It always forwards.See port roles on the topology
Router IDRIDOSPF: The 32-bit identifier a router uses in OSPF, written like an IP address. It names the router in every LSA it originates.OSPF Explorer
Routing tableGeneral: The list of destination prefixes a router knows, with the next hop, exit interface and metric for each.Cost & SPF

S

Shortest Path First (Dijkstra)SPFOSPF: The algorithm each router runs over its link-state database to compute the lowest-cost tree from itself to every destination.Cost & SPF
Signal-to-noise ratioSNRRF & Wireless: How far the wanted signal sits above the noise floor, in dB. It, more than raw signal strength, determines achievable data rate.RF Math Explorer
Spanning Tree ProtocolSTPSpanning Tree: A switch protocol that blocks redundant links so a Layer 2 network has exactly one active path between any two points, preventing broadcast loops.Spanning Tree Explorer
Stub areaOSPF: An area that refuses external LSAs and relies on a default route from its border router, keeping its database small.Multi-area design
Subnet maskAddressing & Subnetting: A 32-bit pattern of leading ones that marks which bits of an address are the network portion — for example 255.255.255.0.Subnetting Lab
Supernetting / route summarizationAddressing & Subnetting: Combining adjacent prefixes into one shorter prefix so routers advertise fewer, larger routes.Subnetting Lab

T

ThroughputGeneral: The useful data actually delivered per second — not the same as link speed. Loss, retransmissions, and overhead all reduce it.Link quality estimator

U

Usable host rangeAddressing & Subnetting: The addresses between the network and broadcast addresses — 2^(host bits) − 2 of them in ordinary IPv4 subnets.Subnetting Lab

V

Variable Length Subnet MaskingVLSMAddressing & Subnetting: Carving one block into subnets of different sizes so each segment gets only the addresses it needs, largest allocated first.Plan a VLSM allocation
VLANSpanning Tree: A virtual LAN — a logically separate Layer 2 broadcast domain carried over shared switch hardware and trunk links.

W

WavelengthλRF & Wireless: The physical length of one cycle, roughly 300 divided by the frequency in MHz (metres). Antenna sizes follow from it.Calculate wavelength
Wildcard maskAddressing & Subnetting: The bitwise inverse of a subnet mask, used in access lists and OSPF network statements. 0 means match, 1 means ignore.Subnetting Lab

Z

Zero compression (IPv6)Number Bases: Replacing one run of all-zero IPv6 groups with '::'. It may appear only once per address so it can be expanded unambiguously.Expand an IPv6 address