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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallAn IP loopback address sends traffic back to the same device that originated it. In IPv4, loopback addresses are in 127.0.0.0/8, most commonly 127.0.0.1; in IPv6, the loopback address is ::1. Neither address identifies another computer on your home or office network.
What does an IP loopback address do?
A loopback address is a host-local IP destination: when a device sends traffic to it, the traffic returns to that same device rather than traveling to another machine. It provides an address-space way for software on a host to communicate with that host through its network stack.
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Loopback traffic must stay within the host. RFC 1122 says IPv4 addresses in the loopback range must not appear outside a host, and RFC 4291 says an IPv6 packet addressed to loopback must never leave a single node or be forwarded by a router (RFC 1122; RFC 4291).
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IPv4: 127.0.0.0/8
The entire IPv4 block 127.0.0.0/8 is designated for loopback. The address most commonly used in practice is 127.0.0.1. RFC 5735 describes the block as looping traffic back inside the host and notes that it is ordinarily implemented using only 127.0.0.1/32 (RFC 5735).
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IPv6: ::1
IPv6 has one loopback address: ::1, written in full as 0:0:0:0:0:0:0:1. RFC 4291 specifies it as ::1/128 and says a node may use it to send an IPv6 packet to itself (RFC 4291, Section 2.5.3).
Is localhost the same as 127.0.0.1?
Not exactly. localhost is a special-use name, while 127.0.0.1 is an IPv4 address. Name-resolution software should resolve localhost names to the appropriate IPv4 or IPv6 loopback address. RFC 6761 also says resolution APIs should not send queries for localhost names to configured caching DNS servers (RFC 6761, Section 6.3).
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Depending on the system and connection, localhost may resolve to either 127.0.0.1 or ::1. That distinction can matter when a service listens on only one IP family.
How does loopback differ from LAN, public, and link-local addresses?
| Address type | Reachability scope | What it targets |
|---|---|---|
| Loopback | One device only | The device sending the traffic |
| Private/local-network | Within a local network | A device on that network, which may be different from the sender |
| Public | Globally reachable in principle | A public network endpoint |
| IPv4 link-local | A single network link | Hosts sharing that link; 169.254.0.0/16 is commonly used when DHCP is unavailable |
These scopes are distinct. For example, 192.168.0.1 can identify a device on a local network, whereas 127.0.0.1 always means the current device. MDN explains the distinction between loopback, local-network, and public address spaces in its overview of local network access (MDN: Local network access).
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Can another computer access a service at your localhost?
No—not by using its own loopback address. If a service is running on Computer A, connecting to 127.0.0.1 or ::1 from Computer B points to Computer B itself, not Computer A. To reach Computer A over a LAN, a client generally needs Computer A’s local-network address, and the service must be configured to accept connections through that interface.
Loopback describes where packets are addressed, not whether an application is secure. It does not establish that a service has authentication, or that the software running on the device is safe.
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Why can a local service work with one address but not the other?
IPv4 and IPv6 loopback are separate destinations. A service listening only on 127.0.0.1 may not accept a connection made to ::1, and the reverse can also be true. When localhost access fails, check which address family the client resolved and which address family the service is listening on. If the client is on a different device, remember that loopback refers to that client’s own host.
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