IPv4 Special Range Calculator

About this interactive

A few IPv4 ranges are set aside, and the first octets say which. Private (RFC 1918): three blocks that any home or company can reuse inside its own network. 10.0.0.0 to 10.255.255.255; 172.16.0.0 to 172.31.255.255 (sixteen networks, 172.16 to 172.31); 192.168.0.0 to 192.168.255.255 (256 networks, 192.168.0 to 192.168.255). Internet routers do not carry them, so traffic from a private address is translated to a public one on its way out. Watch the edges: 172.15 and 172.32 are public, and so are 192.167 and 192.169. Loopback: the whole 127.0.0.0/8 range, with 127.0.0.1 (localhost) the one you will use. Traffic to it never leaves the device, so a ping to it tests the device's own network software, cable or no cable. (The video says the ping fails with the cable unplugged; it does not.) APIPA (link-local): 169.254.0.0/16. A device that gets no answer from a DHCP server picks an address in this range at random. It reaches devices on its own link, but nothing past the router, so seeing 169.254 on a PC usually means DHCP failed. Only 169.254 is APIPA; 169.253 and 169.255 are public. 0.0.0.0: as 0.0.0.0/0 it is the default route, every network at once; it is never a host's address. Public: every other ordinary address, unique on the internet and routed as it is. Type the kind of address exactly as each question names it, and addresses in dotted decimal. Anything you miss shows the answer and how to work it out. Seven of the twenty-six questions are drawn each run.

What you'll learn

Tell a private (RFC 1918) IPv4 address from a public one, including addresses just outside the private blocks, and give each private block's bounds
Recognise loopback (127.0.0.0/8), APIPA (169.254.0.0/16) and the 0.0.0.0 default route from memory, and say what each one means on a device

Aligned to

CompTIA Network+

1.7 Given a scenario, use appropriate IPv4 network addressing.

Cisco CCNA

1.7 Describe private IPv4 addressing.

Cisco CCST Networking

2.1 Compare and contrast private addresses and public addresses.

2.2 Identify IPv4 addresses and subnet formats.

CompTIA A+ Core 1

2.6 Compare and contrast common network configuration concepts.

Key terms

Private IPv4 Address: An IP address from RFC 1918 ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) that is not routable on the public internet and must be translated before traversing it.
Public IP Address: A globally unique IP address assigned to a device or network that is routable and reachable across the public internet.
Loopback Address: The reserved IPv4 address 127.0.0.1 (within the 127.0.0.0/8 range) that a device uses to send traffic to itself, allowing the local network stack to be tested without sending packets onto a physical network. Pinging 127.0.0.1 is a quick way to verify that a device's TCP/IP stack is functioning.
Automatic Private IP Addressing: A feature that automatically assigns a device an IP address in the 169.254.0.0/16 range when it cannot obtain an address from a DHCP server. APIPA allows limited local-network communication but does not provide internet access.
RFC 1918: The internet standard that defines three private IPv4 address ranges reserved for use within private networks and not routable on the public internet.
Default Route: A catch-all routing entry represented as 0.0.0.0/0 (IPv4) or ::/0 (IPv6) that a router uses to forward packets when no more specific matching route exists in the routing table. It is typically configured to point toward the next-hop router or ISP connection.

Topics

Private Addressing Public Addressing Loopback Address Apipa Rfc 1918 Default Route Interactive Calculation

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