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An internal IP address identifies a device or network interface within a private network. In IPv4, the familiar private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These addresses are not directly routable over the public Internet, but a router or other 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 an informal term for an address used within a private network. The more precise description depends on the address family and the address’s scope: private IPv4 addresses are defined by specific ranges, while IPv6 has separate address categories for local use.
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Private describes where an address can be routed; it does not mean the device is disconnected from the Internet. A gateway can translate or proxy traffic between a private network and the Internet. Microsoft describes this role for NAT and proxies in its core network components guidance.
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The three private IPv4 blocks are defined in RFC 1918. The ranges below are technical address allocations, not statistics. Microsoft documents them in its networking guidance and its IPv4 private-address reference.
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| IPv4 range | Prefix | Example |
|---|---|---|
| 10.0.0.0–10.255.255.255 | 10.0.0.0/8 | 10.1.2.3 |
| 172.16.0.0–172.31.255.255 | 172.16.0.0/12 | 172.20.4.5 |
| 192.168.0.0–192.168.255.255 | 192.168.0.0/16 | 192.168.1.1 |
A prefix denotes a block containing many addresses. For example, 192.168.1.1 is one address inside 192.168.0.0/16; it is not the whole private range. A network may use a smaller subnet within one of these blocks.
How internal-use IPv6 addresses differ
The IPv4 private ranges do not apply to IPv6. IPv6 has distinct local-use categories with different scopes. Microsoft’s IPv6 planning guidance describes these two:
| Category | Address space | Scope and Internet routing |
|---|---|---|
| Link-local | IPv6 link-local addresses | Automatically configured on interfaces and limited to one network segment; not Internet-routable. |
| Unique-local | fc00::/7 | For private use; not Internet-routable. |
Both can be used for communication in their intended local scope, but they are not IPv4 private addresses and should not be called RFC 1918 ranges.
What an internal address does—and does not—tell you
- It identifies an endpoint within a network. The address can help devices communicate on the local network or across connected private networks.
- It is not a public Internet endpoint by itself. A private IPv4 or the IPv6 local-use categories above are not directly routable over the public Internet.
- It does not rule out Internet access. A router or gateway can use NAT or a proxy so a device with a private address can send traffic outward.
- Not every non-public address is an internal address. For example, 127.0.0.1 is a loopback address, a separate category; it is not one of the private IPv4 ranges listed above. Microsoft’s private-address reference distinguishes it from those ranges.
Quick way to interpret the term
If you see “internal IP” in a router or network setting, it usually means the address assigned for use inside that network. Check the address family before applying a range rule: the three RFC 1918 blocks are for IPv4, while IPv6 uses its own local-use categories and scopes.
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