Private ipv4 address

As explained in Acing the CCNA Exam: Volume 2 Advanced Networking and Security

A private IPv4 address is an IPv4 address from a designated range intended for internal networks and not required to be globally unique or routable over the public internet.

Private IPv4 addresses support internal networks without requiring globally unique addresses. They conserve IPv4 space, but packets using them cannot travel directly over the public internet. section 9.0 section 9.1

RFC 1918 defines three private IPv4 ranges:

• 10.0.0.0/8 — 10.0.0.0 through 10.255.255.255 section 9.1
• 172.16.0.0/12 — 172.16.0.0 through 172.31.255.255 section 9.1
• 192.168.0.0/16 — 192.168.0.0 through 192.168.255.255 section 9.1

Organizations can reuse these ranges because separate networks do not need unique addresses when they are not directly connected. NAT translates private addresses to public addresses so internal hosts can communicate over the internet. section 9.1 section 9.2

Private host using NAT

PC1 sends a packet sourced from its private address. R1 translates that source address to a public address before forwarding it, then translates the reply back to PC1’s private address. section 9.2.1

Figure 9.1 Public and private IPv4 addresses. Private IPv4 addresses can be freely used for internal networks and do not have to be globally unique. Public IPv4 addresses, used for communication over the internet, must be globally unique.

Compare reusable private LAN ranges with globally unique public IPv4 addresses and observe why overlapping internal subnets can coexist. section 9.1

How Acing the CCNA Exam: Volume 2 Advanced Networking and Security covers it

How deep it goes

Defines RFC 1918 ranges, reuse, and internet non-routability, then connects the concept to NAT without detailing router configuration.

Examples

Uses RFC 1918 ranges, overlapping 192.168.0.0 subnets, and a PC1-to-internet NAT exchange.

What you can do after

Evaluate whether an IPv4 address is private, reusable internally, or dependent on NAT for internet communication.

How it connects

Connects private IPv4 addressing with NAT, public IPv4 addresses, IPv6, and CIDR.

liveBookmanning.com

Read Acing the CCNA Exam: Volume 2 Advanced Networking and Security on liveBook Get the book at manning.com

Related concepts

• IPv4kind of · IPv4 is the fourth version of the Internet Protocol, using 32-bit addresses to identify network interfaces and packet sources or destinations.
• network address translationused by · Network address translation is a networking technique that rewrites IP addresses and often transport-layer ports as traffic crosses a gateway or network boundary.
• public ip addresscontrasts with · A public IPv4 address is a globally unique IPv4 network address routable on the public Internet and assigned to an internet-facing resource.
• unique local addressequivalent to · A unique local address is an IPv6 private unicast address intended for use within internal networks and not for communication over the public internet.
• DNS recordused by · A DNS record is a structured Domain Name System entry associating a domain name with information such as an address, service target, or administrative value.
• ipv4 address exhaustionaddresses · IPv4 address exhaustion is the depletion of available unique IPv4 addresses because demand exceeds the finite 32-bit address space.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 2 Advanced Networking and Security. The section links point to the parts of the book it draws on.