Network Devices
Term | Definition | ||
|---|---|---|---|
| Router | A networking device that forwards data packets between computer networks. | ||
| Switch | A networking device that connects devices within a local area network. | ||
| Modem | A device that modulates digital data into analog signals for transmission over analog communication lines such as telephone lines, and demodulates incoming analog signals into digital data. | ||
| Access Point | A device that allows wireless devices to connect to a wired network using Wi-Fi. | ||
| Network Interface Card | A hardware component that enables a computer to connect to a network. It provides the physical connection between the computer and the network medium, such as Ethernet or Wi-Fi. | ||
| Gateway | A network node that serves as an entry point to another network. It often acts as an intermediary between different types of networks, such as connecting a local network to the internet. | ||
| Repeater | A networking device used to regenerate or replicate signals in order to extend the reach of a network. | ||
| Firewall | A network security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules. It acts as a barrier between a trusted internal network and an untrusted external network (such as the internet), preventing unauthorized access while allowing legitimate traffic to pass through. | ||
| Link | A physical or logical connection between two network devices that allows them to communicate with each other. | ||
Network Topologies
Term | Definition | ||
|---|---|---|---|
| Star Topology | Each network device is connected directly to a central hub or switch. The central hub acts as a central point of connection, facilitating communication between all devices in the network. | ||
| Bus Topology | All network devices are connected to a single communication line. Each device on the network can communicate directly with any other device by transmitting data onto the shared communication line. Can suffer from issues such as signal degradation and collisions, especially as the network grows larger or more devices are added. | ||
| Ring Topology | Each network device is connected to exactly two other devices, forming a closed loop. Data travels in one direction, passing through each device until it reaches its destination. offer high reliability and fault tolerance, as data can still be transmitted even if one device fails. Can suffer from issues such as network congestion and limited scalability. | ||
| Mesh Topology | Each network device is connected directly to every other device in the network. Data can travel from one device to another through multiple paths, providing redundancy and fault tolerance. Can be complex to set up and maintain, and requires a significant amount of cabling. | ||
UDP
Term | Definition | ||
|---|---|---|---|
| Universal Datagram Protocol | A connectionless and unreliable transport protocol. Unlike TCP, UDP does not establish a connection before transmitting data and does not perform error checking, retransmission, or flow control. As a result, UDP is faster and more efficient but less reliable than TCP. | ||
| UDP Header Format |
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| Datagram | A single unit of data transmitted over a network using the UDP protocol. Each datagram is independently routed from the source to the destination, and there is no guarantee of delivery or order preservation. | ||
TCP
Term | Definition | ||
|---|---|---|---|
| TCP | A connection-oriented protocol used for reliable and ordered delivery of data between networked devices in a packet-switched network, such as the Internet. | ||
| TCP Header | used to carry control information about the TCP connection. It is added to the front of each TCP segment transmitted over the network. Contains fields such as source port, destination port, sequence number, acknowledgment number, TCP flags (control bits), window size, checksum, and urgent pointer. | ||
| TCP Handshake | The process used by TCP to establish a connection between two devices. It involves three steps:
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| Flow Control | A mechanism used by TCP to regulate the rate of data transmission between the sender and receiver to prevent the receiver from being overwhelmed by incoming data. Implemented using a sliding window mechanism, where the receiver advertises its available buffer space to the sender, limiting the amount of data the sender can transmit at any given time. | ||
| Congestion Control | A mechanism used by TCP to manage network congestion and prevent packet loss in the event of network congestion. Algorithms dynamically adjust the rate at which data is transmitted based on network conditions, such as packet loss and round-trip time. | ||
| Slow Start | A congestion control mechanism used by TCP to gradually increase the transmission rate of data packets during the initial phase of a connection. In slow start, the sender starts by transmitting a small number of packets and exponentially increases the number of packets transmitted until it reaches a threshold known as the congestion window size. | ||
| Congestion Avoidance | A congestion control mechanism used by TCP to regulate the rate of data transmission once the congestion window size reaches a predefined threshold. The sender increases the congestion window size linearly or additively in response to acknowledgment of transmitted data packets, rather than exponentially as in slow start. | ||
| Fast Retransmit | A congestion control mechanism used by TCP to detect and recover from packet loss more quickly than the standard timeout mechanism. When a sender receives duplicate acknowledgments for the same sequence number, it assumes that a packet has been lost and retransmits the missing packet without waiting for a timeout. | ||
| Additive Increase/Multiplicative Decrease | A congestion control algorithm used by TCP to dynamically adjust the congestion window size based on network conditions. The congestion window size is increased additively when network conditions are favorable and decreased multiplicatively when congestion is detected. This allows TCP to converge to an optimal transmission rate while avoiding network congestion and packet loss. | ||
IP
Term | Definition | ||
|---|---|---|---|
| IP | A network layer protocol responsible for addressing and routing packets of data so that they can be transmitted across networks and reach their destination. | ||
| IP Header | A part of an IP packet that contains control information about the packet, including source and destination IP addresses, packet length, time-to-live (TTL), protocol version, header length, and checksum. Added to the beginning of each IP packet and is used by routers to forward the packet to its destination. | ||
| IP Addressing | A numerical label assigned to each device connected to a network, allowing devices to communicate with each other using the Internet Protocol. | ||
| Subnetting | The process of dividing a single IP network into multiple smaller subnetworks, or subnets, to improve network efficiency and manageability. | ||
| IP Multicasting | A communication technique that allows a single packet to be sent from one sender to multiple recipients simultaneously. | ||
| CIDR Notation | Consists of an IP address followed by a forward slash (/) and a number indicating the number of significant bits in the network prefix. For example, /(192.168.1.0/24/) represents a network with a 24-bit prefix. | ||
| IPv4 | Addresses are 32-bit numerical values represented in dotted-decimal notation and are divided into network and host portions. | ||
| IPv6 | Addresses are 128-bit numerical values represented in hexadecimal notation (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334) and provide a much larger address space than IPv4. | ||
| Unicast | A type of network communication in which data is sent from one sender to one receiver. | ||
| Broadcast | A type of network communication in which data is sent from one sender to all devices on a network. | ||
| Fragmentation | The process of dividing an IP packet into smaller fragments to fit within the maximum transmission unit (MTU) size of a network segment. Occurs when an IP packet is too large to be transmitted over a network without being fragmented, such as when passing through a network with a smaller MTU than the packet size. | ||
| Subnet Mask | A 32-bit numerical value used to divide an IP address into network and host portions in IPv4 addressing. Consists of a series of contiguous binary 1s followed by a series of contiguous binary 0s. The binary 1s represent the network portion of the IP address, while the binary 0s represent the host portion. | ||
Routing Protocols
Term | Definition | ||
|---|---|---|---|
| Routing Protocol | A set of rules and conventions used by routers to determine the best path for forwarding packets from a source to a destination across a network. | ||
| Distance Vector Routing | A type of routing algorithm in which routers exchange routing tables with their neighboring routers. Each router maintains a table that lists the distance (cost) to reach each destination network and the next-hop router to reach that network. | ||
| Link-State Routing | A type of routing algorithm in which routers exchange information about the state of their links with all other routers in the network. Each router constructs a map of the entire network topology based on this information and uses algorithms like Dijkstra's algorithm to compute the shortest path to each destination. | ||
| Hybrid Routing Protocols | Combine characteristics of both Distance Vector and Link-State Routing protocols. | ||
Routing Information Protocol RIP | One of the oldest and simplest Distance Vector Routing protocols. Uses hop count as a metric and advertises routing information to neighboring routers every 30 seconds. Has limitations in large networks due to its slow convergence and limited hop count | ||
| Border Gateway Protocol | An interdomain routing protocol used to exchange routing information between autonomous systems on the Internet. A Distance Vector Routing protocol that takes into account policies and attributes to make routing decisions. | ||
| Bellman-Ford Algorithm | A dynamic programming algorithm used to find the shortest path from a source node to all other nodes in a weighted graph. It is used in Distance Vector Routing protocols. | ||
| Djikstra's Algorihtm | A greedy algorithm used to find the shortest path from a source node to all other nodes in a graph with non-negative edge weights. It is used in Link-State Routing protocols. | ||
| Routing Table | A data structure stored in a router that contains information about known networks and the next-hop routers to reach those networks. | ||
| Route Poisoning | A technique used in routing protocols to prevent routing loops by marking a route as unreachable when a link or destination becomes unavailable. When a router detects that a route is no longer valid, it sends an update to its neighboring routers indicating that the route has a infinite metric. | ||
| Split Horizon | A technique used in routing algorithms to prevent routing loops in Distance Vector routing protocols. With Split Horizon, a router does not advertise routes back out the interface through which they were learned. This prevents a router from advertising a route back to the router from which it was received, which can cause loops in the network topology. | ||
DNS
Term | Definition | ||
|---|---|---|---|
| DNS | A hierarchical and distributed naming system for computers, services, or any resource connected to the Internet or a private network. DNS translates domain names (e.g., www.example.com) into IP addresses (e.g., 192.0.2.1) to facilitate the routing of data over the Internet. | ||
| Domain | A logical grouping of network resources, such as computers, servers, and devices, that share a common naming scheme. | ||
| Subdomain | A subdivision of a domain that is part of a larger domain namespace. Created by adding a prefix to the main domain name, separated by dots. For example, in the domain name "mail.example.com," "mail" is a subdomain of "example.com." | ||
| Authoritative Server | A DNS server that has the original and definitive DNS records for a particular domain. Authoritative servers are responsible for providing authoritative answers to DNS queries about domain names within their zone of authority. | ||
| Recursive Query | A type of DNS query in which a DNS resolver requests information from other DNS servers on behalf of a client and recursively follows the chain of DNS servers until it receives a complete answer. The resolver then returns the answer to the client. | ||
| Iterative Query | A type of DNS query in which a DNS resolver requests information from another DNS server and expects a partial or referral response. If the queried DNS server does not have the requested information, it provides a referral to another DNS server closer to the authoritative source. The resolver then continues to query DNS servers iteratively until it receives a complete answer. | ||
| DNS Caching | A mechanism used by DNS resolvers to store previously resolved DNS query results for a certain period of time. Helps improve DNS query performance by reducing the need to repeatedly query authoritative DNS servers for frequently accessed domain names. | ||
| A Records | DNS resource records used to map domain names to IPv4 addresses. | ||
| MX Records | DNS resource records used to specify the mail servers responsible for receiving email messages for a domain. | ||
| NS Records | DNS resource records used to specify the authoritative DNS servers for a domain. | ||
| Hostname | A label assigned to a device connected to a network, such as a computer or server, that identifies it within the network. | ||
HTTP/HTTPS
Term | Definition | ||
|---|---|---|---|
HTTP Hypertext Transfer Protocol | Protocol used for transferring hypertext documents, such as HTML files, over the World Wide Web. | ||
| HTTPS | An extension of HTTP used for secure communication over a computer network, typically the Internet. Encrypts the data transmitted between a client and a server using SSL/TLS protocols, providing confidentiality, integrity, and authentication. | ||
| GET Request | HTTP request method used by clients to retrieve data from a server. | ||
| POST Request | HTTP request method used by clients to submit data to a server to be processed or stored. | ||
| PUT Request | HTTP request method used by clients to upload data to a server, replacing the current representation of the target resource with the uploaded data. | ||
| DELETE Request | HTTP request method used by clients to request the removal of a resource from a server. | ||
| SSL/TLS | Provide a secure and encrypted connection between clients and servers, ensuring confidentiality, integrity, and authenticity of data transmitted over the network. Use a handshake protocol to establish a secure connection between a client and a server. During the handshake, the client and server negotiate encryption algorithms, exchange cryptographic keys, and authenticate each other's identities. | ||
| HTTP/2 | A major revision of the HTTP network protocol used by the World Wide Web. Introduces features such as multiplexing, header compression, and server push to reduce latency and improve throughput. | ||
| HTTP/3 | Based on the QUIC (Quick UDP Internet Connections) transport protocol and is designed to further improve performance, security, and reliability. | ||
URLs Uniform Resource Locators | Used to specify the location of resources on the web. | ||
| Status Codes | Three-digit numbers included in responses to indicate the outcome of a request. Common examples include 200 (OK, request successful), 404 (Not Found, requested resource not found), 500 (Internal Server Error, server encountered an error), and others. | ||
| Methods | Various verbs that indicate the desired action to be performed on a resource. | ||
| Digital Certificate | Issued by trusted certificate authorities (CAs) to verify the authenticity of servers and establish secure connections. Contain information such as the server's public key, domain name, and the CA's digital signature. | ||
Email Servers
Term | Definition | ||
|---|---|---|---|
| SMTP | A protocol used for sending email messages between servers over the Internet. It is a text-based protocol that operates on TCP port 25. Responsible for delivering outgoing email messages from a sender's email client or server to the recipient's email server. | ||
| SMTP Commands |
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| POP3 | A protocol used for retrieving email messages from a mail server to a client device, such as a computer or mobile device. It is a client-server protocol that operates on TCP port 110. | ||
| POP3 Commands |
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| IMAP | A protocol used for accessing and managing email messages stored on a remote mail server. Allows users to view, organize, and manage email messages directly on the server without downloading them. Operates on TCP port 143. | ||
| IMAP Commands |
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Reliable Data Transport
Term | Definition | ||
|---|---|---|---|
Reliable Data Transport RDT | The process of transmitting data between two networked devices in a manner that ensures data integrity, delivery, and sequencing. These protocols are designed to handle issues such as packet loss, duplication, and reordering, which can occur in unreliable network environments. | ||
| Sequence Number | A unique identifier assigned to each data unit transmitted over a network. | ||
| Acknowledgement | A message sent by the receiver to the sender to confirm the successful receipt of a data unit. Allows the sender to detect packet loss and retransmit any missing or corrupted data units. | ||
| Window | A range of sequence numbers that can be transmitted without waiting for acknowledgments. | ||
| Checksum | A value calculated from the contents of a data unit that is used to detect errors during transmission. Checksums are typically appended to data units before transmission and recalculated by the receiver upon receipt. If the recalculated checksum at the receiver does not match the checksum transmitted with the data unit, it indicates that the data unit may have been corrupted during transmission. | ||
| Stop-and-Wait | A simple protocol used for reliable data transmission in which the sender transmits a single data unit and then waits for an acknowledgment from the receiver before sending the next data unit. This process continues sequentially until all data units have been transmitted. | ||
| Go-Back-N | A sliding window protocol used for reliable data transmission in which the sender can transmit multiple data units without waiting for individual acknowledgments. However, if the sender detects a timeout or a missing acknowledgment, it retransmits all unacknowledged data units from the beginning of the window. | ||
| Selective Repeat | A sliding window protocol used for reliable data transmission in which the sender can transmit multiple data units without waiting for individual acknowledgments. However, if the sender detects a timeout or a missing acknowledgment, it retransmits only the specific unacknowledged data units. | ||
| Timeout | A predefined period during which the sender expects to receive an acknowledgment for a transmitted data unit. If the sender does not receive an acknowledgment within the period, it assumes that the data unit was lost or corrupted during transmission and initiates a retransmission. | ||
Data Transmission
Term | Definition | ||
|---|---|---|---|
| Packet | A unit of data that is transmitted over a network. It consists of a header and a payload. The header contains control information, such as source and destination addresses, while the payload contains the actual data being transmitted. | ||
| Latency | The time it takes for a packet to travel from its source to its destination. | ||
| Bandwidth | The maximum rate at which data can be transmitted over a network link. | ||
| Throughput | The actual rate of successful data transmission over a network link. It takes into account factors such as latency, packet loss, and network congestion, and it represents the effective data transfer rate achieved in real-world network conditions. | ||
| Packet Loss | Occurs when one or more packets fail to reach their destination during transmission over a network. It can be caused by factors such as network congestion, hardware failures, or errors in transmission. | ||
| Packet Switching | A method of transmitting data over a network in which data is divided into packets before transmission. Each packet is individually routed to its destination based on information contained in the packet header. | ||
| Circuit Switching | An alternative method of establishing connections in a network, where a dedicated communication path is established between the source and destination before data transmission begins. This dedicated circuit remains active for the duration of the communication session, providing a consistent and predictable level of bandwidth. | ||
| Transmission Delay | The time it takes to push all the packet's bits onto the link. | ||
| Propogation Delay | The time it takes for a signal to travel from the sender to the receiver over the transmission medium. | ||
| Queuing Delay | The time a packet spends waiting in a queue before it can be transmitted over a network link. It occurs when the network link is busy and cannot immediately transmit the packet. | ||
| Processing Delay | The time it takes for a networking device, such as a router or a switch, to process a packet once it has been received. | ||
MAC Addressing
Term | Definition | ||
|---|---|---|---|
Media Access Control MAC | Responsible for controlling access to the physical network medium and for uniquely identifying devices on a network. Defines rules for how devices on a network can access the shared communication medium without interference. | ||
| MAC Address | A unique identifier assigned to a network interface controller by its manufacturer. Typically represented as a series of six groups of hexadecimal digits (e.g., 00:1A:2B:3C:4D:5E). | ||
| VLAN | A logical network segment created within a physical network infrastructure. Allow network administrators to group devices into separate broadcast domains regardless of their physical location. | ||
| CAM Table | A data structure used by Ethernet switches to map MAC addresses to the corresponding switch ports. When a switch receives an Ethernet frame, it examines the source MAC address of the frame and updates this table with the MAC address and the port on which the frame was received. This information is used to forward subsequent frames to the correct destination ports efficiently. | ||
| Address Resolution Protocol | A protocol used to map IP addresses to MAC addresses in a local network. When a device wants to communicate with another device on the same subnet, it needs to know the MAC address corresponding to the destination IP address. | ||
Carrier Sense Multiple Access with Collision Detection CSMA/CD | In this protocol, a device listens to the communication medium to detect if it is currently in use (carrier sense). If the medium is idle, the device starts transmitting its data. However, if the medium is busy, the device defers its transmission and waits for a random backoff time before retrying. If multiple devices attempt to transmit data simultaneously, a collision may occur. The protocol detects collisions by monitoring the communication medium while transmitting data. Upon detecting a collision, the transmitting device stops sending data, sends a jam signal to notify other devices of the collision, and enters a collision recovery process where it waits for a random amount of time before attempting to retransmit. | ||
Carrier Sense Multiple Access with Collision Avoidance CSMA/CA | In this protocol, a device listens to the communication medium to detect if it is currently in use. To avoid collisions, devices use a process called the Distributed Coordination Function (DCF). DCF involves the use of random backoff timers before initiating transmissions to reduce the likelihood of collisions. Additionally, devices may employ techniques such as Request to Send (RTS) and Clear to Send (CTS) frames to reserve the medium and prevent collisions in environments with high contention. | ||
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