Learn These 123 Diagrams — And You'll Understand All Common Network System Terms

> Source: ruodian360.com

> Original Publication: 2022-11-02

> Category: Network Communication

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With 177 networking terms and 123 illustrations, this article needed careful organization. To make it easy to navigate, the terms are arranged according to the network layering model and its extensions, divided into 15 categories for quick reference.

1. Network Basics

1. Circuit Switching: A communication method where a dedicated communication path (circuit) is established between two parties before data transmission begins. The channel remains reserved for the entire duration of the session and is released only when communication ends.

2. Packet Switching: A technique that divides data into smaller message blocks (packets), which are then routed independently across the network to the destination.

3. Network Protocol: A set of standards or rules that define how data is formatted, transmitted, and received over a network, ensuring interoperability between different devices and systems.

4. Protocol Stack: A layered implementation of network protocols, where each layer provides services to the layer above and relies on services from the layer below (e.g., the TCP/IP protocol stack).

5. World Wide Web (WWW): A global information space where resources are identified by URLs, accessed via HTTP/HTTPS, and available over the Internet.

6. Local Area Network (LAN): A network that interconnects devices within a limited area such as a home, office, or building.

7. Metropolitan Area Network (MAN): A network larger than a LAN, covering a geographic area ranging from a large campus to an entire metropolitan region.

8. Wide Area Network (WAN): A telecommunications network that extends over a large geographic area, connecting multiple LANs across cities, countries, or continents.

9. Internet: A global computer network that connects millions of devices worldwide using Internet protocols, enabling worldwide communication and data exchange.

10. Internet of Things (IoT): A network of physical devices embedded with electronics and connectivity that enables them to collect, exchange, and act on data.

11. Cloud Computing: A model for delivering on-demand computing resources—servers, storage, databases, software—over the Internet on a pay-as-you-go basis.

12. Big Data: The practice of analyzing extremely large and complex datasets using aggregated computing resources to discover patterns, correlations, and insights that guide decision-making.

13. Software-Defined Networking (SDN): An architecture that separates the control plane from the data plane, enabling centralized, programmable network management and greater flexibility.

14. Data Plane / Forwarding Plane: The part of a network device responsible for making forwarding decisions and actually forwarding data packets.

15. Control Plane: The part of a network device responsible for controlling how forwarding is done, including running routing protocols and maintaining routing tables.

2. Operating Systems

1. Operating System (OS): A software platform installed on smart devices that abstracts hardware differences and provides a portable environment for application programs.

2. Graphical User Interface (GUI): A visual interface that allows users to interact with a device by clicking icons, buttons, and other graphical elements.

3. Command-Line Interface (CLI): A text-based interface where users type commands to operate the device.

4. RAM (Random Access Memory): Volatile memory used in both computers and network devices to store temporary data during operation. Contents are lost when power is removed.

5. Flash Memory: Non-volatile storage in network devices, similar to a hard drive in computers, used to store the operating system and other large files.

6. NVRAM (Non-Volatile Random Access Memory): Memory that preserves its contents when power is off. Used in network devices to store the startup configuration file.

7. Console Port: A management port on network devices. By connecting a terminal to the console port via a console cable and using terminal emulation software, administrators can perform local management.

3. Network Protocols

1. OSI Model: A conceptual framework that divides network communication functions into seven distinct layers, from physical transmission to application services.

2. TCP/IP Model: Also called the Internet protocol suite. The communication model used by the Internet, derived from TCP and IP, consisting of four layers.

3. Application Layer: Layer 7 of the OSI model and Layer 4 of the TCP/IP model. The layer closest to end users, where network applications communicate. In the TCP/IP model it conceptually includes OSI Layers 5 (Session) and 6 (Presentation).

4. Transport Layer: Layer 4 of the OSI model and Layer 3 of the TCP/IP model. Responsible for end-to-end data transport, including segmentation, flow control, and error recovery.

5. Network Layer: Layer 3 of the OSI model. Handles routing packets from source to destination across multiple networks.

6. Packet: A unit of data encapsulated by network layer protocol headers.

7. Data Link Layer: Layer 2 of the OSI model. Manages data transfer between directly connected nodes. Also detects and corrects errors introduced by the physical layer.

8. Frame: A unit of data encapsulated by data link layer protocol headers and trailers.

9. Physical Layer: Layer 1 of the OSI model. Defines the electrical, mechanical, and physical standards for transmitting raw bit streams between devices.

10. Internet Layer: Layer 2 of the TCP/IP model, functionally equivalent to the OSI Network Layer. Handles packet addressing and routing across networks.

11. Network Access Layer: Layer 1 of the TCP/IP model. Defines how data is transmitted between directly connected nodes on the same network segment. Combines the OSI Physical and Data Link layers.

12. Encapsulation: The process where each layer of the protocol stack adds its own header (and sometimes trailer) to data as it travels down the stack before transmission.

13. Decapsulation: The reverse of encapsulation: the receiving device strips off each layer's header as data travels up the protocol stack to recover the original payload.

14. Header: Protocol-specific control information prepended to data according to the protocol specification during encapsulation.

4. Network Access Layer

1. Twisted Pair Cable: A transmission medium made of pairs of insulated copper wires twisted together to cancel electromagnetic interference.

2. Optical Fiber: A glass or plastic fiber that transmits data as light pulses using total internal reflection, enabling high-speed communication over long distances.

3. IEEE 802.3: The IEEE standard for Ethernet networks, defining the physical and MAC sub-layer specifications for wired LANs.

4. IEEE 802.11: The IEEE standard for Wireless Local Area Networks (WLANs), commonly known as Wi-Fi.

5. Parity Check: An error-detection method where the receiver counts the number of 1-bits in received data and compares it against an expected parity (even or odd) to detect changes.

6. Checksum: An error-detection technique where a checksum value calculated from the data is included in the transmission. The receiver recalculates and compares.

7. Cyclic Redundancy Check (CRC): A robust error-detection method that uses polynomial division to compute a checksum. More reliable than parity or simple checksums.

8. Shared Ethernet: An Ethernet environment where all devices share a single collision domain and must contend for transmission opportunities.

9. Binary: A base-2 number system using only digits 0 and 1. The fundamental numeric representation in all digital systems.

10. Hexadecimal: A base-16 number system using digits 0-9 and letters A-F. Commonly used in networking to represent MAC addresses and IPv6 addresses compactly.

11. Collision Domain: A network segment where devices share the same transmission medium, and only one device can transmit at a time without causing collisions.

12. Switched Ethernet: An Ethernet environment where each device connects to a central switch via a dedicated point-to-point link, eliminating the need for transmission contention.

13. MAC Address: A 48-bit hardware address, expressed in hexadecimal, burned into a network interface card (NIC) and used at the data link layer for device identification.

14. Broadcast Domain: A logical network segment where any device can receive broadcast frames sent by other devices. Routers separate broadcast domains.

5. Switching Networks

1. Collision: Interference that occurs when multiple devices on a shared medium transmit simultaneously, corrupting all transmitted frames.

2. Hub: A physical-layer device with multiple ports that connects devices in a shared Ethernet. It broadcasts incoming data out through all other ports.

3. Bridge: A two-port data-link-layer device that builds a MAC-to-port mapping table and forwards frames based on MAC addresses. Each port is a separate collision domain.

4. Switch: A multiport bridge operating at the data link layer. Each switch port is an independent collision domain. Networks built with switches use switched Ethernet.

5. Switching Capacity: The maximum data switching capability of a switch, measured in bits per second (bit/s). Also called backplane bandwidth.

6. Packet Forwarding Rate: The number of packets a switch can forward per second, measured in packets per second (pps).

7. Interface Speed: The number of bits a switch interface can transmit per second, measured in bit/s.

8. Duplex Mode: A mode describing whether an interface can transmit and receive data simultaneously.

9. Half-Duplex Mode: An interface mode where data can be transmitted and received, but not at the same time.

10. Full-Duplex Mode: An interface mode where data can be transmitted and received simultaneously.

11. MAC Address Table: A database on a switch that records mappings between MAC addresses and switch ports. The switch uses this table to make forwarding decisions.

6. VLAN (Virtual Local Area Network)

1. VLAN (Virtual Local Area Network): A logical partition of a physical LAN into multiple isolated broadcast domains. VLANs limit network size, reduce broadcast traffic, and improve security.

2. VLAN Tag: A 4-byte field inserted into an Ethernet frame header to identify the VLAN to which the frame belongs.

3. Tagged Frame: An Ethernet frame that carries a VLAN tag in its header. Typically exchanged between switches to preserve VLAN information.

4. Untagged Frame: An Ethernet frame without a VLAN tag. End devices typically send untagged frames.

5. PVID (Port VLAN ID): A parameter on a switch port that assigns a default VLAN ID to untagged frames received on that port.

6. Access Port: A switch port that connects to end devices, carrying traffic for a single VLAN and stripping tags before forwarding.

7. Trunk Port: A switch port that connects switches to each other, carrying traffic for multiple VLANs using 802.1Q tagging.

8. Hybrid Port: A switch port that can connect to either end devices or other switches, offering flexible VLAN membership behavior.

9. Static VLAN: A VLAN manually configured by a network administrator on a switch.

10. Dynamic VLAN: A VLAN assigned dynamically based on the MAC address or other properties of the connected device.

7. STP (Spanning Tree Protocol)

1. Root Bridge: Also called the root switch. The switch in a spanning-tree network that serves as the reference point for all path cost calculations.

2. Root Port: The port on a non-root bridge that provides the best (lowest-cost) path to the root bridge.

3. Designated Port: The port on each network segment responsible for forwarding data toward the root bridge. Each segment has exactly one designated port.

4. Alternate Port: A port placed in a blocking state that cannot forward data. It can assume the root port role if the current root port or its link fails.

5. BPDU (Bridge Protocol Data Unit): STP messages exchanged between switches containing bridge ID, root bridge ID, and path cost information. Used to elect the root bridge and determine port roles.

6. Configuration BPDU: BPDUs sent by the root bridge at regular Hello intervals. Non-root switches receive them on root ports and forward them via designated ports.

7. TCN BPDU (Topology Change Notification): BPDUs generated by a non-root switch that detects a topology change. They are forwarded to the root bridge, which updates its BPDUs to reflect the change.

8. Bridge ID: A value composed of an STP priority and the switch's MAC address, used in root bridge elections.

9. Root Path Cost (RPC): The cumulative cost of all outgoing port costs along the path from a switch to the root bridge.

10. Port ID: A value composed of a port priority and port number, used in STP elections to break ties between ports.

11. Edge Port: An RSTP feature that allows a port connected to an end device to transition directly to the forwarding state, skipping learning and listening states.

12. Proposal/Agreement (P/A) Mechanism: An RSTP mechanism that enables designated ports on point-to-point links to transition quickly to forwarding without waiting for the forward delay timer.

13. Point-to-Point Port: A port operating in full-duplex mode, connected to exactly one other switch.

14. Shared Port: A port operating in half-duplex mode, potentially connected to a shared medium like a hub.

15. MSTP (Multiple Spanning Tree Protocol): An IEEE 802.1s protocol that maps multiple VLANs to fewer spanning tree instances, reducing the number of STP computations while allowing load balancing.

8. Network Layer

1. IPv4 (Internet Protocol version 4): The fourth version of the Internet Protocol, using 32-bit addresses. Although its address space is exhausted, it remains the most widely deployed network layer protocol.

2. IPv6 (Internet Protocol version 6): The most recent version of the Internet Protocol, using 128-bit addresses. It provides a vastly larger address space, improved security, and better auto-configuration.

3. Packet Fragmentation: The process of splitting a packet into smaller fragments when its size exceeds the Maximum Transmission Unit (MTU) of the outgoing link.

4. Routing: The process of selecting paths in a network to forward packets. Also refers to an entry in the routing table that describes a path to a destination network.

5. Routing Table: A data table stored in a router or layer-3 switch containing route entries used to determine the best next hop for forwarding packets.

6. Routing Protocol: A protocol that defines how routers exchange path information, what information they share, and how they calculate the best paths to destination networks.

7. Distance Vector Routing Protocol: A routing protocol where routers exchange distance and direction information, and each router computes its best paths based on information from neighbors.

8. Link-State Routing Protocol: A routing protocol where routers exchange link-state information, giving each router a complete view of the network topology to independently compute best paths.

9. Longest Prefix Match: A forwarding rule where the router selects the route with the longest subnet mask when multiple routes match a destination IP address, ensuring the most specific route is used.

9. Subnetting

1. Subnet Mask: A 32-bit value in dotted-decimal notation that identifies which bits of an IP address represent the network portion and which represent the host portion.

2. Network Bits: The leading bits of an IP address (as indicated by the subnet mask) that identify the network the device belongs to.

3. Host Bits: The trailing bits of an IP address that identify a specific host within a network.

4. Classful Addressing: An addressing scheme that divides IP addresses into fixed classes (A, B, C, D, E) based on the first few bits, with predetermined network/host boundaries.

5. Classless Addressing (CIDR): An addressing scheme that removes class boundaries, allowing variable-length subnet masks (VLSM) for more efficient address allocation.

6. Unicast: One-to-one transmission where a packet is sent from a single source to a single destination.

7. Multicast: One-to-many transmission where a packet is sent to a multicast group address, and only devices that have joined the group receive it.

8. ARP (Address Resolution Protocol): A protocol that resolves a destination device's MAC address from its known IP address on a local network.

10. Static Routing

1. Route Entry: An entry in a routing table containing a destination network, next-hop address, and outgoing interface. The router matches packets against these entries to forward them.

2. Administrative Distance / Route Preference: A value used to select the best route when multiple routes to the same destination are learned from different routing sources. Lower values are preferred.

3. Metric: A value used to select the best route among multiple routes learned from the same routing protocol. Lower metrics indicate better paths.

4. Directly Connected Route: A route to a subnet directly attached to a router interface. It appears automatically when the interface is operational.

5. Static Route: A route manually configured by a network administrator on a router.

6. Default Route: A route with a 0-bit prefix length (mask 0.0.0.0) that matches any destination. Used as the route of last resort.

7. Dynamic Route: A route learned through a dynamic routing protocol such as OSPF, RIP, or BGP.

8. Floating Static Route: A static route configured with a higher administrative distance than the primary route, serving as a backup that activates only when the primary route fails.

9. Summary Route (Route Aggregation): A single route entry that represents multiple more-specific subnet routes, reducing the routing table size.

10. Layer 3 Topology: A logical topology showing network addresses and the routing paths that routers use to forward packets between networks.

11. Physical Topology: A diagram showing the physical connections and cabling between network devices.

12. Inter-VLAN Routing: Routing traffic between different VLANs based on IP addresses, enabling communication across VLAN boundaries.

13. Layer 3 Switch: A switch with integrated Layer 3 (routing) capabilities, able to route between VLANs at hardware speed.

14. VLANIF Interface: A virtual Layer 3 interface on a Layer 3 switch that serves as the default gateway for hosts in a specific VLAN.

11. Dynamic Routing

1. Classful Routing Protocol: A routing protocol that does not include subnet mask information in its route advertisements.

2. Classless Routing Protocol: A routing protocol that includes subnet mask information in its route advertisements, supporting VLSM and CIDR.

3. LSA (Link-State Advertisement): A data unit used by link-state routing protocols to advertise information about network links and their states.

4. RIP (Routing Information Protocol): A distance-vector routing protocol that uses hop count as its metric. One of the oldest interior gateway protocols.

5. Update Timer: In RIP, the interval at which a router periodically sends routing updates, defaulting to 30 seconds.

6. Aging Timer (Invalid Timer): In RIP, the time (default 180 seconds) after which a route is marked unreachable if no update is received for it.

7. Garbage Collection Timer (Flush Timer): In RIP, the time (default 120 seconds) between marking a route as unreachable and deleting it from the routing table.

8. Split Horizon: A loop-prevention technique where a router never advertises a route back out of the interface from which it was learned.

9. Poison Reverse: A loop-prevention technique where a router advertises an unreachable metric for a route back out of the interface on which it was learned.

10. Route Poisoning: A technique where a router advertises a failed route as having an infinite (unreachable) metric to alert other routers of the failure.

11. Triggered Update: A mechanism where a router sends routing updates immediately upon detecting a network change, without waiting for the update timer.

12. OSPF (Open Shortest Path First)

1. OSPF Neighbor Table: A table on an OSPF router that records neighboring routers and their adjacency states.

2. OSPF Topology Table (Link-State Database): A database containing all LSAs received from routers within the same OSPF area, forming a complete network topology view.

3. OSPF Network Type: The network type assigned to an OSPF interface, such as Broadcast, Point-to-Point (P2P), NBMA, or Point-to-MultiPoint (P2MP).

4. Router ID (RID): A 32-bit value that uniquely identifies a router within an OSPF domain.

5. DR (Designated Router) and BDR (Backup Designated Router): OSPF roles on multi-access networks that reduce management traffic by centralizing LSA exchanges. The BDR takes over if the DR fails.

6. LSA (Link-State Advertisement): Messages exchanged between OSPF routers to synchronize their link-state databases.

7. OSPF Backbone Area (Area 0): The central OSPF area to which all other areas must connect, either physically or via a virtual link.

8. Internal Router: An OSPF router whose all interfaces belong to the same area.

9. Backbone Router: An OSPF router that has at least one interface in Area 0 (the backbone).

10. ABR (Area Border Router): An OSPF router with interfaces in multiple areas. It summarizes routing information between areas.

11. ASBR (Autonomous System Boundary Router): An OSPF router that imports external routes from other routing protocols or ASs into the OSPF domain.

12. OSPF Virtual Link: A logical link that connects a non-backbone area to Area 0 when a direct physical connection is not available.

13. Router LSA (Type 1): Type-1 LSA generated by every OSPF router, advertising its directly connected links. Flooded only within the originating area.

14. Network LSA (Type 2): Type-2 LSA generated by the DR on multi-access networks, listing all attached routers. Flooded only within the originating area.

15. Network Summary LSA (Type 3): Type-3 LSA generated by ABRs to advertise routes between areas. Flooded within the originating area.

16. ASBR Summary LSA (Type 4): Type-4 LSA generated by ABRs to advertise the location of an ASBR to other areas. Flooded within the originating area.

17. External LSA (Type 5): Type-5 LSA generated by ASBRs to advertise external routes throughout the OSPF domain.

18. NSSA External LSA (Type 7): Type-7 LSA generated by ASBRs in a Not-So-Stubby Area (NSSA), flooded only within the NSSA.

13. Transport Layer

1. TCP (Transmission Control Protocol): A connection-oriented transport protocol providing reliable, ordered delivery of data between application processes.

2. UDP (User Datagram Protocol): A connectionless transport protocol providing best-effort delivery with minimal overhead and lower latency than TCP.

3. Port Number: A 16-bit number (0-65535) identifying application processes at the transport layer. IANA-managed ranges: Well-known (0-1023), Registered (1024-49151), Dynamic (49152-65535).

4. Well-Known Ports: Ports 0-1023 assigned to specific services, enabling clients to locate standard servers on a network.

5. Registered Ports: Ports 1024-49151 assigned to user-installed applications. Clients may dynamically select a source port from this range.

6. Dynamic/Private Ports: Ports 49152-65535 dynamically assigned as source ports by clients when initiating connections.

7. Socket: A combination of an IP address and a port number (IP:port) that uniquely identifies an application process on a device.

8. TCP Connection: A logical connection established between a client and server before data transfer begins, identified by the source and destination IPs and ports.

9. Three-Way Handshake: The three-message process (SYN, SYN-ACK, ACK) used by TCP to establish a reliable connection between two hosts.

10. Sliding Window: A TCP flow-control mechanism where the receiver advertises its available buffer space, allowing the sender to adjust its transmission rate.

14. Application Layer

1. Client-Server Model: An application architecture where dedicated servers provide services to clients that request them.

2. Peer-to-Peer (P2P) Model: An application architecture where hosts communicate as peers with equal status, both providing and consuming services.

3. Client: A host that initiates communication by requesting services. Also refers to the client software itself.

4. Server: A host that accepts requests and provides services to clients.

5. Telnet: An application-layer protocol for remote terminal access, allowing a client to manage a remote device over the network.

6. Shell: An operating system interface that accepts user commands and executes them.

7. SSH (Secure Shell): A secure application-layer protocol for encrypted remote management sessions.

8. DHCP (Dynamic Host Configuration Protocol): A protocol that automatically assigns IP addresses and other configuration parameters to devices on a network.

9. DNS (Domain Name System): An application-layer protocol that translates human-readable domain names into IP addresses.

10. Web (World Wide Web): An interconnected system of hypertext documents and resources accessible over the Internet.

11. HTTP (Hypertext Transfer Protocol): An application-layer protocol for transmitting hypertext (web content) between clients and servers.

12. SSL (Secure Sockets Layer): A security protocol developed by Netscape that encrypts and authenticates communication between a client and server.

13. TLS (Transport Layer Security): The IETF-standardized evolution of SSL, providing secure encrypted communication between applications.

14. HTTPS (HTTP over SSL/TLS): HTTP encrypted and authenticated via SSL/TLS, ensuring secure transmission of web content.

15. User Agent: In email architecture, the client application used by end users to compose, send, and receive email.

16. SMTP (Simple Mail Transfer Protocol): An application-layer protocol that defines how email messages are transferred between mail servers.

17. Mail Access Protocol: A protocol defining how a recipient's email client retrieves messages from a mail server.

18. POP3 (Post Office Protocol version 3): An application-layer protocol for retrieving email from a mail server, typically downloading and optionally deleting messages.

15. Network Management

1. Directory: A hierarchical structure in the file system for organizing files, equivalent to folders in Windows.

2. Startup Configuration File: The saved configuration that a network device loads and applies during boot-up.

3. VTY (Virtual Teletype) Line/Interface: A virtual interface providing remote management access to a network device via Telnet or SSH.