A+ Core 1 • Mission 06 • Module 6
Configuring Network Addressing and Internet Connections — connect Internet services, understand TCP/IP, recognize IPv4 vs IPv6, work with subnet masks, ports, DHCP, DNS, VLANs, and VPNs.
IP = Internet ProtocolIPv4 = Internet Protocol version 4IPv6 = Internet Protocol version 6CIDR = Classless Inter-Domain RoutingAPIPA = Automatic Private IP AddressingNAT = Network Address TranslationTCP = Transmission Control ProtocolUDP = User Datagram ProtocolDHCP = Dynamic Host Configuration ProtocolDNS = Domain Name SystemVLAN = Virtual Local Area NetworkVPN = Virtual Private Network
An Internet Protocol (IP) address is a logical address assigned to a network interface. It helps devices identify where network traffic is coming from and where it needs to go. A device can have more than one IP address—for example, one on Wi-Fi and another on Ethernet.
Internet Protocol version 4 (IPv4) is 32 bits and is normally written as four decimal numbers (octets), each from 0–255.
Example: 192.168.1.25
Internet Protocol version 6 (IPv6) is 128 bits and is written with hexadecimal digits separated by colons.
Example: 2001:db8::25
Private IPv4 addresses are used inside homes, schools, and organizations. They are not routed directly across the public Internet. A router commonly uses Network Address Translation (NAT) so many private devices can communicate outward using public addressing.
Public IP addresses are globally routable addresses used to communicate across the Internet. Your router's Internet-facing connection may receive a public address from the Internet Service Provider (ISP).
| Private range | What the prefix means | Student-friendly memory |
|---|---|---|
| 10.0.0.0/8 10.0.0.0–10.255.255.255 | /8 means the first 8 bits—the first octet—are the network prefix for this range. Every address here starts with 10. | “Starts with 10? Private 10 range.” |
| 172.16.0.0/12 172.16.0.0–172.31.255.255 | /12 fixes the first 12 bits. For recognition, remember that only 172.16 through 172.31 are in this private block. | “172 private lives from 16 through 31.” 172.15.x.x and 172.32.x.x are not in this private range. |
| 192.168.0.0/16 192.168.0.0–192.168.255.255 | /16 means the first 16 bits—the first two octets—are the network prefix for this range. These addresses start with 192.168. | “192.168 = private.” This pattern is common on home/local networks. |
10.x.x.x, 172.16–31.x.x, and 192.168.x.x are not different “types” of private network. They are three address blocks reserved for private use. A network administrator or router manufacturer chooses a block and then divides it into subnets that fit the network.
Your device normally receives its local/private IP address from the network it joins. The address is not permanently tied to the laptop or phone.
At home you might receive 192.168.1.25. At school the same laptop might receive 10.42.7.25. On another organization's network it could receive 172.20.8.25. All three can be valid private addresses.
The network's addressing plan determines the range. Dynamic Host Configuration Protocol (DHCP) commonly assigns an available address from the subnet configured by the administrator/router.
Suppose a home router uses 192.168.1.0/24. A laptop might be 192.168.1.25, a phone 192.168.1.40, and a printer 192.168.1.60. Those addresses work inside that local network. The router's Internet/Wide Area Network (WAN) side has a separate upstream address. Network Address Translation (NAT) lets many inside private addresses share the router's Internet-facing connectivity.
They are on different private networks with different addressing plans. Both ranges are valid for private IPv4 use.
No. Only 172.16.0.0 through 172.31.255.255 is the private 172 block.
Yes. Private addresses can be reused on separate local networks because they are not globally routed as unique public Internet addresses.
On many networks, DHCP on the router or a network server assigns an address from that network's configured subnet.
Classless Inter-Domain Routing (CIDR) uses /1 through /32 to tell you how many of IPv4's 32 bits belong to the network prefix. The slash number is a bit count—not a separate part of the IP address.
IPv4 has four octets. Each octet has 8 bits, so 8 + 8 + 8 + 8 = 32 bits.
Octet 1 | Octet 2 | Octet 3 | Octet 4
00000000 . 00000000 . 00000000 . 00000000
As the CIDR number increases from /1 → /32, the network/host boundary moves one bit to the right. Each step turns one more mask bit from 0 into 1.
| CIDR range | Changing octet | What is happening |
|---|---|---|
| /1–/8 | Octet 1 | The boundary moves through the first 8 bits. |
| /9–/16 | Octet 2 | Octet 1 is all network; the boundary moves through Octet 2. |
| /17–/24 | Octet 3 | Octets 1–2 are all network; the boundary moves through Octet 3. |
| /25–/32 | Octet 4 | Octets 1–3 are all network; the boundary moves through Octet 4. |
| Bits ON | Binary in changing octet | Mask value | Magic number / jump |
|---|---|---|---|
| 1 | 10000000 | 128 | 128 |
| 2 | 11000000 | 192 | 64 |
| 3 | 11100000 | 224 | 32 |
| 4 | 11110000 | 240 | 16 |
| 5 | 11111000 | 248 | 8 |
| 6 | 11111100 | 252 | 4 |
| 7 | 11111110 | 254 | 2 |
| 8 | 11111111 | 255 | 1 |
This is the same pattern for /1–/8, /9–/16, /17–/24, and /25–/32. Only the changing octet is different.
/14 is in Octet 2. It uses 6 network bits in the changing octet: 11111100 = 252. Its mask is 255.252.0.0 and the magic number in Octet 2 is 256 − 252 = 4.
/30 is in Octet 4. It also uses 6 network bits in the changing octet: 11111100 = 252. Its mask is 255.255.255.252 and the magic number in Octet 4 is also 4.
Connection: the 8-bit pattern repeats; CIDR tells you which octet contains that pattern.
Settings: Settings → Network & internet → Wi-Fi or Ethernet → select the connected network / Properties and look for IPv4 address, IPv6 address, DNS, and related network properties.
Command line: open Command Prompt and run ipconfig. Use ipconfig /all for more detail such as DHCP and DNS information.
Settings: System Settings → Network → select Wi-Fi or Ethernet → Details. Look at the TCP/IP information.
Terminal: tools such as ifconfig can display interface addressing.
Settings → Wi-Fi → tap the ⓘ information button beside the connected network. Look for the IP Address section, including IPv4 details such as IP address, subnet mask, and router.
Open Settings → Network/Internet or Connections → Wi-Fi → select the connected network. The exact labels vary by manufacturer and Android version; look under network details/advanced information for the IP address, gateway, and related settings.
Open a terminal and use ip addr (often shortened to ip a) to see addresses on network interfaces. ip route helps identify routes/default gateway information.
In the router's administration interface, the WAN/Internet status area may show the address used toward the ISP, while the LAN/DHCP/client area shows local addressing and connected devices. Interface names vary by router.
It says the network prefix uses 24 bits. IPv4 has 32 bits total, leaving 8 host bits.
Private. Every IPv4 address beginning with 10 is inside 10.0.0.0/8.
No. The private 172 block is only 172.16.0.0 through 172.31.255.255.
2001:db8::20. The hexadecimal digits and colons are the quick visual clue.
Modern networks can use both protocol versions at the same time. This is commonly called dual stack.
Network properties in Windows Settings or run ipconfig in Command Prompt.
IP address: identifies a host/interface logically.
Subnet mask/prefix: identifies which bits represent the network vs host portion.
Default gateway: router address used to reach other networks.
DNS server: helps resolve names to IP addresses.
| Type | Connection / device clue | Key idea |
|---|---|---|
| DSL | Telephone copper; DSL modem; splitter/filter | Asymmetric can have faster download than upload; symmetric is equal. |
| Cable | Coax + F-type; cable modem; DOCSIS | Uses cable TV infrastructure. |
| Fiber | FTTC / FTTP; ONT | FTTP brings fiber into the premises; FTTC transitions to copper before the premises. |
| Satellite / fixed wireless | Antenna / WISP / satellite | Useful where wired service is limited; satellite can have higher latency. |
| Cellular | 3G/4G/LTE/5G | Mobile radio Internet access. |
Router: forwards based on IP addresses between networks. Firewall: can allow/deny traffic using rules/ACLs based on packet information such as IP, MAC, protocol, and port.
| Layer | Main job | Address / PDU clue |
|---|---|---|
| Application | High-level network functionality. | Data |
| Transport | TCP vs UDP; ports. | Segment (module terminology) |
| Internet | Communication between network segments. | IP address • Packet |
| Link / Network Interface | Communication on local segment. | MAC address • Frame |
This chart works across /1 through /32. Instead of memorizing only /24–/30, first find the CIDR prefix in the correct octet column. Then read across to find the mask value and the address jump (magic number).
| Bits used in changing octet | Octet 1 | Octet 2 | Octet 3 | Octet 4 | Changing mask value | Subnets in that octet | Address jump / magic number |
|---|---|---|---|---|---|---|---|
| 1 bit | /1 | /9 | /17 | /25 | 128 | 2 | 128 |
| 2 bits | /2 | /10 | /18 | /26 | 192 | 4 | 64 |
| 3 bits | /3 | /11 | /19 | /27 | 224 | 8 | 32 |
| 4 bits | /4 | /12 | /20 | /28 | 240 | 16 | 16 |
| 5 bits | /5 | /13 | /21 | /29 | 248 | 32 | 8 |
| 6 bits | /6 | /14 | /22 | /30 | 252 | 64 | 4 |
| 7 bits | /7 | /15 | /23 | /31 | 254 | 128 | 2 |
| 8 bits | /8 | /16 | /24 | /32 | 255 | 256 | 1 |
/20 is in Octet 3 because /17–/24 live there. On the /20 row, the changing mask value is 240. Magic number: 256 − 240 = 16. Count Octet 3 ranges: 0, 16, 32, 48… The IP has 2 in Octet 3, so it is in the 0–15 range. Network: 192.168.0.0/20. Broadcast: 192.168.15.255.
/26 is in Octet 4 and uses the 2-bit row. Changing mask = 192. 256 − 192 = 64, so ranges start 0, 64, 128, 192.
Octet 2. /9–/16 belong to Octet 2. /14 uses 6 bits in that octet: mask value 252 and jump 4.
Classless Inter-Domain Routing (CIDR) uses slash notation for the network prefix. Choose any prefix from /1 through /32. Watch the network/host boundary move one bit at a time across all four octets; the subnet mask, changing octet, binary bits, magic number, and address range update together.
32 bits, written as four decimal octets separated by dots. Each octet is 0–255.
Private ranges:
10.0.0.0–10.255.255.255
172.16.0.0–172.31.255.255
192.168.0.0–192.168.255.255
APIPA: 169.254.0.1–169.254.255.254 in the module. It is automatically assigned when normal address configuration through DHCP is unavailable.
NAT: translates between private and public addressing.
128 bits, written in hexadecimal as eight 16-bit values separated by colons, with abbreviation rules allowing shorter notation.
Example: 2001:db8:0:0:0:0:0:10 can be written 2001:db8::10.
Fast recognition: dotted decimal such as 192.168.1.20 is IPv4; hexadecimal groups separated by colons such as 2001:db8::20 are IPv6.
Dual stack: a system/network can use IPv4 and IPv6 together.
TCP: connection-oriented with sequencing/acknowledgment; the module highlights the three-way handshake: SYN → SYN/ACK → ACK.
UDP: connectionless with no sequencing or acknowledgments; lower overhead for appropriate services.
FTP 20/21 • SSH 22 • Telnet 23 • SMTP 25 • DNS 53 • DHCP 67/68 • HTTP 80 • POP3 110 • NetBIOS 137–139 • IMAP 143 • LDAP 389 • HTTPS 443 • SMB 445 • RDP 3389
Automatically configures hosts. Know scope, lease, reservation, MAC address, and DORA: Discover → Offer → Request → Acknowledge.
Resolves FQDN/host names to IP addresses. Resolution can involve local information/cache, a DNS server, authoritative/TLD/root infrastructure.
Domain Name System (DNS) is the Internet's naming system. A DNS record answers a specific kind of question about a domain. Do not memorize only the letters—connect each record to the job it performs.
| Record | Meaning / job | Example question it answers |
|---|---|---|
| A | Maps a hostname to an IPv4 address. | “What IPv4 address should I use for www.example.com?” |
| AAAA | Maps a hostname to an IPv6 address. Think “A record, but large enough for IPv6.” | “What IPv6 address should I use for this host?” |
| CNAME | Canonical Name: makes one hostname an alias of another hostname. | “Should shop.example.com point to another DNS name?” |
| MX | Mail Exchanger: identifies the mail server(s) that receive email for a domain; priority values can indicate preference. | “Where should mail for @example.com be delivered?” |
| TXT | Stores text data. Often used for verification and email-security information such as SPF/DKIM/DMARC-related data. | “What verification/security text has this domain published?” |
| SRV | Service record: identifies a service's hostname and port. | “Which server/port provides this service?” |
| NS | Name Server: identifies authoritative DNS servers for a DNS zone. | “Which DNS server is authoritative for this zone?” |
| PTR | Pointer: reverse lookup from an IP address toward a hostname. | “What hostname is associated with this IP?” |
| SOA | Start of Authority: contains core administrative information about a DNS zone. | “What is the authoritative/administrative starting information for this zone?” |
https://www.example.com/page.Email-related DNS protections in the module: SPF, DKIM, DMARC.
Logically splits broadcast domains on switching infrastructure. Used for performance, security, and controlling communication between groups.
Creates a secure tunnel for remote traffic across an untrusted/non-secure connection, such as public Wi-Fi.
Recognize APIPA. Check link, adapter state, DHCP availability, and lease process.
Investigate Domain Name System (DNS) configuration/resolution.
Check default gateway/router and upstream connectivity.
Check duplicate static addresses and subnet settings.
Which IPv4 bits are the network portion and which are available for host addressing.
IPv6. It uses hexadecimal groups and colons.
IPv4. It uses four dotted-decimal octets.
Define it before revealing it.
IPv4 and private. 192.168.0.0/16 is a private IPv4 range.
DHCP/connectivity. The address is in the APIPA range.
It is a subnet mask equivalent to /24: 24 network bits and 8 host bits.
A record. AAAA is for IPv6.
Discover → Offer → Request → Acknowledge.
Internet layer in the four-layer TCP/IP model.