Network Engineer Course - Chapter 3: IP Addressing, Subnetting, DNS, and the OSI Model

Vocabulary flashcards covering core concepts of IP addressing, IPv4 and IPv6 structures, subnetting, DHCP, DNS, the 7-layer OSI model, and physical cabling topology (MDF/IDF).

IP address (Internet Protocol address)

A numerical label assigned to each device connected to a network using the Internet Protocol; it identifies the device's network interface and provides its location on the network so data can be routed to it.

IPv4

An Internet Protocol version that defines an address as a $32$-bit number, written as four decimal numbers separated by dots (octets), yielding approximately $4.3\text{ billion}$ ($2^{32}$) possible addresses.

IPv6

An Internet Protocol version that defines an address as a $128$-bit number written in hexadecimal across eight groups of four digits separated by colons, yielding approximately $340\text{ undecillion}$ ($2^{128}$) addresses.

IP packet

The Layer $3$ unit of data carried by the Internet Protocol; it contains the data payload along with header fields (such as source and destination IP addresses) needed by routers to route it.

Time to Live (TTL)

An IPv4 header counter that is decremented by $1$ at every router hop; when it reaches $0$, the packet is discarded to prevent endless circulation in routing loops.

Octet

A block of $8\text{ bits}$ (one byte); one of the four numbers making up an IPv4 address, each ranging from $0$ to $255$.

Network part

The portion of an IP address that identifies the specific network to which an address belongs, shared by all devices residing on that same network.

Host part

The portion of an IP address that uniquely identifies a specific device or interface within a given network.

Subnet mask

A $32$-bit value consisting of consecutive binary $1\text{s}$ followed by consecutive binary $0\text{s}$, written like an IP address, that indicates which bits represent the network part and which represent the host part.

CIDR (Classless Inter-Domain Routing)

A slash notation shorthand (such as $/24$) indicating the number of network bits in an address, replacing legacy fixed address classes with variable mask lengths.

Bitwise AND

The logical operation a host performs between an IP address and its subnet mask to isolate the network portion, determining whether a destination IP is on the local network or a remote network.

Default gateway

The local router IP address that a device sends packets to whenever the destination address is determined to be outside its own local subnet.

ARP (Address Resolution Protocol)

A protocol that discovers the Layer $2$ MAC address of a destination on the local network by broadcasting a query containing the target's IP address.

Public IP address

A globally unique IP address assigned by an ISP that can communicate directly across the global internet and is required for hosting publicly reachable servers.

Private IP address

An IP address reserved for use inside private local networks (Class A: $10.0.0.0/8$, Class B: $172.16.0.0/12$, Class C: $192.168.0.0/16$) that is not routable on the public internet.

NAT (Network Address Translation)

A router service that replaces a client device's private source IP address with a public IP address on outbound packets and translates incoming response traffic back to the originating private IP.

PAT (Port Address Translation / Overload)

The most common form of NAT, enabling multiple internal private IP hosts to share a single public IP address by tracking sessions using distinct transport port numbers.

Port forwarding

A configured router rule that forwards unsolicited incoming public internet traffic arriving on a specific port to a preselected internal private IP host.

Network address

The reserved first address of a subnet in which all host bits are binary $0$; it represents the network itself and cannot be assigned to any individual device.

Broadcast address

The reserved last address of a subnet in which all host bits are binary $1$; packets addressed to it are processed by every host on that subnet, so it cannot be assigned to an individual device.

Loopback address

A reserved IPv4 range ($127.0.0.0$ to $127.255.255.255$, typically $127.0.0.1$) and IPv6 address ($::1$) allowing a device to send data to itself to test its own local TCP/IP stack without physical network connectivity.

APIPA (Automatic Private IP Addressing)

A link-local mechanism that self-assigns an address in the range $169.254.0.1$ to $169.254.255.254$ when a host fails to receive an IP lease from a DHCP server.

Static IP address

An IP address configured manually on a device that remains fixed, commonly assigned to servers, printers, and router interfaces.

Dynamic IP address

An IP address assigned automatically to a client device by a DHCP server for a finite lease duration.

DHCP (Dynamic Host Configuration Protocol)

A network protocol that automatically provides connecting devices with an IP address, subnet mask, default gateway, and DNS server addresses.

DORA

The four-message sequence used by DHCP to allocate IP settings: Discover (broadcast by client), Offer (sent by server), Request (selected by client), and Acknowledge (confirmed by server).

DHCP reservation

A configuration on a DHCP server that permanently ties a specific IP address to a client's unique MAC address, ensuring that device always receives the same address.

DHCP relay

A router service that forwards broadcast DHCP client messages across network boundaries to a DHCP server located on a different subnet.

Subnet (Subnetwork)

A smaller, logically separate segment formed by dividing a larger IP network, establishing smaller broadcast domains for better performance, security, and address efficiency.

Subnetting

The process of borrowing host bits to expand the network portion of an address, creating more subnets with fewer hosts per subnet.

Block size

The total number of IP addresses included within an individual subnet; calculated as $256$ minus the decimal subnet mask value in the interesting octet.

Interesting octet

The specific octet within an IPv4 subnet mask whose value is neither $255$ nor $0$, identifying where subnet boundaries and block increments take place.

VLSM (Variable Length Subnet Masking)

The practice of dividing a network into subnets of different sizes to precisely match the host capacity requirements of different departments or links without wasting addresses.

Dual stack

The transition mechanism that enables a network device or router to run both IPv4 and IPv6 protocol stacks concurrently on the same network interface.

DNS (Domain Name System)

A hierarchical, distributed system that translates human-readable domain names into numerical IP addresses needed by computers to locate services.

DNS resolver

A DNS server or service (often assigned via DHCP) that queries root, TLD, and authoritative nameservers on behalf of client hosts to resolve domain names.

Authoritative server

The specific DNS nameserver that maintains the master records and official answers for a domain zone.

TLD (Top-Level Domain)

The rightmost segment of a domain name (such as .com or .org), managed by designated registry operators beneath the DNS root.

OSI model (Open Systems Interconnection)

A conceptual seven-layer framework that standardizes network communication functions, dividing duties from physical transmission up to user application interfaces.

Physical layer (Layer 1)

The bottom OSI layer responsible for transmitting raw bits across media via electrical voltages, optical pulses, or radio frequencies; includes cables, connectors, and hubs.

Data Link layer (Layer 2)

The OSI layer responsible for node-to-node frame delivery across a local network using physical MAC addresses, error detection, and framing; home to network switches and access points.

Network layer (Layer 3)

The OSI layer that handles logical addressing (IP), path selection, packet routing between distinct networks, and fragmentation; home to routers and Layer $3$ switches.

Transport layer (Layer 4)

The OSI layer that provides end-to-end data transport using segments (TCP) or datagrams (UDP), managing flow control, port addressing, and optional reliability mechanisms.

Session layer (Layer 5)

The OSI layer responsible for establishing, coordinating, maintaining, and terminating dialogue sessions between communicating applications.

Presentation layer (Layer 6)

The OSI layer that formats, translates, compresses, and encrypts/decrypts data (e.g., SSL/TLS, JPEG, ASCII) into a structure usable by applications.

Application layer (Layer 7)

The top OSI layer providing direct network services and protocol interfaces to user software, including HTTP, HTTPS, FTP, SMTP, and DNS.

Encapsulation

The process whereby application data moves down the network stack, with each protocol layer wrapping the received data unit in its own header (and trailer at Layer $2$).

TCP (Transmission Control Protocol)

A reliable, connection-oriented Transport layer protocol that uses a three-way handshake, sequencing, acknowledgments, and retransmission to guarantee ordered data delivery.

UDP (User Datagram Protocol)

A connectionless, lightweight Transport layer protocol that delivers packets with low overhead and high speed, offering no delivery or ordering guarantees.

MDF (Main Distribution Frame)

The primary central equipment room in a facility (such as a server room or data center) where service provider lines terminate and core switches, routers, and firewalls connect to IDFs.

IDF (Intermediate Distribution Frame)

A secondary wiring closet located on a specific floor or building wing that houses access switches and patch panels connecting horizontal cabling to user workstations.

Demarc (Demarcation point)

The precise physical boundary where the external service provider's telecommunications infrastructure ends and the customer's private premises wiring begins.

Backbone cabling

High-capacity network cabling (such as fiber optic or Cat 6a) that interconnects the centralized MDF to distributed IDFs across a building or campus.

Horizontal cabling

Cabling (such as Cat 6 copper) extending from an IDF access switch out to endpoint wall jacks, restricted to a maximum permanent run of $90\text{ meters}$ ($100\text{ meters}$ total including patch cables).

Access point (AP)

A network hardware device wired into an IDF access switch that broadcasts Wi-Fi signals to bridge wireless mobile clients onto the local wired network.