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A+ Core 1 · CompTIA 220-1201 V15 · Objective 2.6

Given a scenario, configure basic wired/wireless small office/home office (SOHO) networks

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Objective 2.6: Given a scenario, configure basic wired/wireless small office/home office (SOHO) networks

Cert: CompTIA A+ Core 1 (220-1201) V15 Domain: 2.0 Networking Weight: ~23% of Core 1 Depth: Given a scenario, configure. Apply IP addressing concepts in a real SOHO context.

What this objective tests

You should understand IPv4 and IPv6 addressing basics, the difference between private and public addresses, when APIPA happens, how subnet masks and default gateways work, and the difference between static and dynamic addressing in a SOHO context.

Key facts

IPv4 (Internet Protocol version 4):

  • 32-bit address, written as four octets in decimal (e.g., 192.168.1.1).
  • About 4.3 billion possible addresses. Long since exhausted publicly, hence widespread use of private addressing and NAT.

Private IPv4 address ranges (RFC 1918):

  • 10.0.0.0/8 (10.0.0.0 to 10.255.255.255)
  • 172.16.0.0/12 (172.16.0.0 to 172.31.255.255)
  • 192.168.0.0/16 (192.168.0.0 to 192.168.255.255)

Private addresses are used inside organizations and homes. They are not routed on the public internet. Devices reach the internet by going through a router that performs Network Address Translation (NAT).

Public IPv4 addresses:

  • Everything else. Routable on the public internet. Globally unique. Allocated by regional internet registries.

IPv6 (Internet Protocol version 6):

  • 128-bit address, written as eight groups of four hex digits separated by colons (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).
  • Address space is effectively unlimited for everyday purposes.
  • Designed to eventually replace IPv4. Coexists with IPv4 (dual stack) during the long transition.

APIPA (Automatic Private IP Addressing):

  • Range 169.254.0.0/16. Self-assigned by a device when DHCP fails.
  • Communicates only with other APIPA devices on the same network segment. Cannot reach the internet.
  • An APIPA address (169.254.x.x) is a strong signal that DHCP is broken.

Static vs dynamic addressing:

  • Static. Manually configured on the device. Stable and predictable. Used for servers, printers, network gear, anything that needs a known address. Risk: misconfiguration leads to IP conflicts or unreachable devices.
  • Dynamic (DHCP). Address assigned automatically by a DHCP server. Best for clients (workstations, phones, guests). Address can change over time (within scope).

Subnet mask:

  • Tells the device which part of the IP address is the network and which part is the host.
  • Common SOHO mask: 255.255.255.0 (also written /24). Defines a network with up to 254 usable hosts.
  • The subnet mask must match the network design. A wrong mask makes devices think other LAN devices are on a different network and routes traffic incorrectly.

Default gateway:

  • The IP address of the router that handles traffic leaving the local network.
  • A workstation with no gateway can talk to its local network but cannot reach the internet.

Common gotchas

  • APIPA address visible. Whenever you see a 169.254.x.x address, DHCP is failing somewhere. Investigate the DHCP server, scope exhaustion, or VLAN misalignment.
  • Subnet mask mismatch. Two devices in the same physical network with different subnet masks may think the other is on a remote network. They try to route through the gateway instead of communicating directly.
  • Missing default gateway. Local traffic works; internet does not. A common misconfiguration on static-IP devices.
  • DHCP-given gateway vs static gateway conflict. Setting a static IP without setting the gateway, then plugging into a network that previously gave DHCP, sometimes leaves stale config that masks the issue.
  • IPv4 / IPv6 dual stack quirks. Some apps prefer IPv6 and behave oddly when only IPv4 is reachable, or vice versa. Knowing the host's IPv4 and IPv6 configuration helps troubleshoot.
  • 172.16-31 confusion. Many people remember 10.x and 192.168.x but forget that 172.16.0.0/12 (specifically 172.16.0.0 through 172.31.255.255) is also private. 172.32.x.x is NOT private.
  • 127.0.0.1 vs 169.254.x.x. 127.0.0.1 is the loopback address (always points to the local machine). 169.254 is APIPA (used when DHCP fails). They are different.

Real-world context

For typical Revtek SOHO setups:

  • Internet circuit (cable, fiber, or DSL) into the modem.
  • ISP-issued IP is public. Router does NAT, hands out private IPs internally.
  • Internal LAN: 192.168.1.0/24 or similar. DHCP scope covers most of the range. Reservations for printers, server-like devices, infrastructure.
  • Subnet mask 255.255.255.0. Default gateway is the router (often .1).

Common helpdesk calls:

  • "I can't get on the internet." Check the workstation's IP. If 169.254.x.x, DHCP is failing. If a regular RFC1918 address, check the default gateway and DNS.
  • "I plugged in my laptop and got an IP conflict warning." Static IP duplicate, or a device with the same static IP came online elsewhere.
  • "I can ping my own subnet but not anywhere else." Default gateway missing or unreachable.

Sources

  • [CompTIA A+ 220-1201 Exam Objectives Version 4.0, Section 2.6](../../../../../../30-RevyTechJourney/CompTIA%20A%2B%20220-1201%20Exam%20Objectives%20%284.0%29.pdf)
  • [Wikipedia: IPv4](https://en.wikipedia.org/wiki/IPv4)
  • [Wikipedia: IPv6](https://en.wikipedia.org/wiki/IPv6)
  • [Wikipedia: Private network](https://en.wikipedia.org/wiki/Private_network)
  • [Wikipedia: Link-local address](https://en.wikipedia.org/wiki/Link-local_address)
  • [Wikipedia: Network address translation](https://en.wikipedia.org/wiki/Network_address_translation)
  • [RFC 1918: Address Allocation for Private Internets](https://datatracker.ietf.org/doc/html/rfc1918)