An internal IP address identifies a device or network interface within a private network. Private IPv4 addresses are not directly routable over the public Internet, but a router or gateway can use network address translation (NAT) or a proxy to let devices using them reach the Internet.
What “internal IP address” means
“Internal IP address” is a common, informal term for an address used inside a private network, such as a home or workplace network. For IPv4, the formal private address ranges are defined by specific blocks. IPv6 has distinct address categories used for local or private communication; the IPv4 blocks do not apply to IPv6.
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An address’s “private” status describes its scope and routing, not whether the device can access the Internet. A gateway can forward traffic between a private network and the Internet, commonly using NAT or a proxy. Microsoft describes this distinction in its core network components guidance and IP address management glossary.
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Private IPv4 address ranges
The three private IPv4 blocks are defined in RFC 1918. The ranges and prefixes are documented in Microsoft’s core network components guidance and its IPv4 private-address reference.
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| IPv4 block | Address range | Example |
|---|---|---|
| 10.0.0.0/8 | 10.0.0.0–10.255.255.255 | 10.0.0.1 |
| 172.16.0.0/12 | 172.16.0.0–172.31.255.255 | 172.16.0.1 |
| 192.168.0.0/16 | 192.168.0.0–192.168.255.255 | 192.168.1.1 |
A prefix describes a whole block, not one address. For example, 192.168.1.1 is one address within 192.168.0.0/16; it is not the entire private range. The precise subnet used by a local network may be smaller than that block.
How IPv6 internal-use addresses differ
IPv6 does not use the RFC 1918 IPv4 ranges. Two IPv6 categories relevant to local and private networking are link-local and unique-local addresses, described in Microsoft’s IPv6 planning guidance.
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| Category | Address family and scope | Public Internet routability |
|---|---|---|
| Private IPv4 | IPv4; used within private networks. Defined blocks are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. | Not directly routable on the public Internet. |
| Link-local | IPv6; applies on one network segment and is automatically configured on interfaces. | Not Internet-routable. |
| Unique-local | IPv6; private-use addresses in fc00::/7. | Not Internet-routable. |
What an internal address does—and does not—tell you
- It identifies an endpoint within a network. A device can have an address for its network interface and use it to communicate locally.
- It does not rule out Internet access. Devices with private addresses can reach the Internet through a gateway that uses NAT or a proxy.
- It is not the same as every non-public or special-purpose address. For example, 127.0.0.1 is a loopback address, not one of the private IPv4 blocks. Microsoft’s IPv4 private-address reference treats it separately.
Microsoft’s IP address planning guidance for Azure virtual networks also discusses address planning in virtual networks; the private IPv4 ranges above remain the relevant blocks when identifying RFC 1918 addresses.
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