openssl 

Command-line interface for the OpenSSL cryptographic toolkit.

X.509 

Standard defining the structure and semantics of digital certificates.

PEM 

Text-based encoding wrapper for cryptographic objects.

DER 

Binary encoding format for ASN.1 data structures.

CSR 

A signed request containing a public key and subject identity.

CA 

Trusted entity that signs and issues certificates.

PFX / P12 

Encrypted container bundling private key, certificate, and chain.

DN 

Structured identity block describing the certificate subject.

CN 

Human-readable name within a Distinguished Name.

O 

Organization name within a Distinguished Name.

OU 

Department or team name within a Distinguished Name.

C 

ISO country code within a Distinguished Name.

ST 

Region or state within a Distinguished Name.

L 

City or locality within a Distinguished Name.

SAN 

X.509 extension listing all identities a certificate is valid for.

DNS 

Hierarchical naming system used to resolve hostnames to IP addresses.

IP 

Numerical addressing scheme used to identify hosts on IP networks.

URI 

Structured identifier for naming or locating resources.

DNS [SAN]

Hostname identity entry within a SAN extension.

IP [SAN]

IP address identity entry within a SAN extension.

URI [SAN]

Structured service identity entry within a SAN extension.

Unicode 

Universal character set assigning a unique code point to every character across all writing systems.

ASCII 

7-bit character encoding defining 128 characters.

Code Point 

Unique numerical identifier assigned to a Unicode character.

Glyph 

Visual representation of a Unicode character rendered by a font.

Unicode Block 

Contiguous range of code points allocated to related characters.

Script 

Collection of characters used to write one or more languages.

Symbol 

Character not belonging to a writing script.

General Category 

Unicode property classifying characters by semantic role.

Unicode Plane 

Subdivision of the Unicode code space into ranges of 65,536 code points.

BMP 

Plane 0 of Unicode covering the most commonly used characters.

SMP 

Unicode plane containing historic scripts and emojis.

UTF-8 

Variable-length encoding for Unicode using 1–4 bytes.

UTF-16 

Variable-length Unicode encoding using 2 or 4 bytes.

UTF-32 

Fixed-length Unicode encoding using 4 bytes per character.

Unicode Normalization 

Process of converting text to a canonical representation.

NFC 

Canonical composed normalization form.

NFD 

Canonical decomposed normalization form.

Homoglyph Attack 

Attack using visually similar Unicode characters to deceive users.

Trojan Source 

Attack exploiting bidirectional Unicode controls to alter code appearance.

Zero-Width Characters 

Unicode characters with no visible glyph.

Bidirectional Algorithm 

Unicode algorithm for displaying mixed RTL and LTR text.

Text Segmentation 

Rules for splitting text into graphemes, words, and sentences.

OSPF 

Link-state Interior Gateway Protocol that synchronizes a distributed topological database and derives routing decisions using Dijkstra’s SPF algorithm.

LSDB 

Synchronized database containing all LSAs within an OSPF area.

LSA 

Topology information unit flooded between OSPF routers.

SPF 

Algorithm used to compute shortest paths from the LSDB.

Hello 

OSPF packet used for neighbor discovery and liveness detection.

Adjacency 

Full synchronization relationship between OSPF neighbors.

Router ID 

32-bit identifier uniquely identifying an OSPF router.

Area 

Logical grouping of routers sharing the same LSDB.

DR 

Router elected on broadcast networks to reduce adjacency scaling.

BDR 

Standby router ready to assume DR responsibilities.

Cost 

Metric used by OSPF to calculate shortest paths.

Reference Bandwidth 

Global value used to calculate interface cost.

Type 1 LSA 

Router LSA describing links from a router within an area.

Type 2 LSA 

Network LSA generated by DR describing multi-access networks.

Type 3 LSA 

Summary LSA describing inter-area routes.

Type 5 LSA 

External LSA describing redistributed routes.

Convergence 

Process by which routers reach a consistent LSDB and routing state.

RIB 

Logical routing table maintained in the control plane.

FIB 

Hardware-optimized forwarding table derived from the RIB.

CEF 

Cisco’s high-performance Layer 3 forwarding architecture.

Control Plane 

Logical plane responsible for routing decisions and protocol computation.

Data Plane 

Plane responsible for forwarding user traffic based on FIB entries.

SPT 

Tree structure generated by SPF computation.

Flooding 

Reliable propagation mechanism used to distribute LSAs.

Authentication 

Mechanism used to validate OSPF packet integrity and peer legitimacy.

Neighbor 

Router discovered via Hello exchange.

Down 

Initial OSPF neighbor state where no Hello has been received.

Init 

State indicating a Hello has been received but bidirectional communication is not yet confirmed.

2-Way 

State where bidirectional Hello exchange is confirmed.

ExStart 

State where master/slave negotiation and DBD sequence exchange begins.

Exchange 

State where routers exchange DBD packets summarizing LSAs.

Loading 

State where routers request and receive missing LSAs.

Full 

State indicating LSDB synchronization between neighbors is complete.

DBD 

Packet used to summarize LSDB contents during adjacency formation.

LSR 

Packet requesting specific LSAs during database synchronization.

LSU 

Packet carrying full LSAs for synchronization or flooding.

LSAck 

Packet acknowledging receipt of LSAs to ensure reliable flooding.

ABR 

Router connecting multiple OSPF areas.

ASBR 

Router redistributing external routes into OSPF.

Backbone 

Area 0 of OSPF serving as the core transit area.

NSSA 

Area type allowing limited external route redistribution.

NBMA 

Network type supporting multiple routers without native multicast.

Type 4 LSA 

ASBR Summary LSA advertising reachability to an ASBR.

Type 6 LSA 

Multicast OSPF LSA (MOSPF extension).

Type 7 LSA 

NSSA External LSA translated to Type 5 by ABR.

Type 8 LSA 

Link LSA used in OSPFv3 for link-local information.

Type 9 LSA 

Opaque LSA with link-local scope.

Type 10 LSA 

Opaque LSA with area scope.

Type 11 LSA 

Opaque LSA with autonomous system scope.

LLDP 

Vendor-neutral Layer 2 protocol (IEEE 802.1AB) used to advertise device identity and capabilities to directly connected neighbors.

LLDPDU 

Complete LLDP payload consisting of a sequence of TLVs carried inside an Ethernet frame.

Neighbor 

The last device that sent an LLDP frame on a given interface.

advertisement 

Unidirectional LLDP frame containing structured metadata about a device.

TLV 

Encoding format used to represent all LLDP information.

Chassis ID 

TLV identifying the sending device.

Port ID 

TLV identifying the sending interface.

TTL 

Lifetime in seconds of an LLDP advertisement in the neighbor table.

System Name 

TLV containing the hostname of the device.

System Description 

TLV describing operating system, platform, or software version.

System Capabilities 

TLV describing device roles such as bridge, router, or access point.

Management Address 

TLV containing reachable management IP address(es).

TLV Type 127 

Organizationally specific TLV used for vendor extensions.

End of LLDPDU 

TLV marking the end of the LLDP frame.

Link-Local 

Traffic scope limited to a single Layer 2 segment.

LLDP Multicast MAC 

Destination MAC address 01:80:C2:00:00:0E used by LLDP.

EtherType 0x88CC 

EtherType value used to identify LLDP frames.

Control Plane 

Plane responsible for generating, processing, and storing LLDP data.

Data Plane 

Plane responsible for transmitting LLDP frames and forwarding traffic.

LLDP Neighbor Table 

Local cache of received LLDP advertisements.

CoPP 

Mechanism that rate-limits traffic to the control plane.

Native VLAN 

Default untagged VLAN on a trunk link.