127.0.0.0/8: The Loopback Range

Everyone knows 127.0.0.1 as localhost, but the whole 127.0.0.0/8 block — over 16 million addresses — is reserved for loopback. Any of them sends traffic back to the same machine.

127.0.0.0/8 at a glance

Address range
127.0.0.0 – 127.255.255.255
Usable hosts
16,777,214
Total addresses
16,777,216
First usable
127.0.0.1
Last usable
127.255.255.254
Subnet mask
255.0.0.0
Wildcard mask
0.255.255.255
Type
Loopback (RFC 1122)

Is an address inside 127.0.0.0/8?

Yes — 127.0.0.53 is inside 127.0.0.0/8. It is address number 53 in the block (counting from 0).

What 127.0.0.0/8 is

Packets to any 127.x.x.x address never leave the host. The operating system loops them back in software.

This means you can run several services on the same port by binding each to a different loopback address, e.g. one on 127.0.0.2:53 and another on 127.0.0.3:53.

Who uses it

  • systemd-resolved

    Ubuntu and other systemd distros run a local DNS stub on 127.0.0.53.

  • Debian and Ubuntu hostnames

    /etc/hosts often maps the machine's hostname to 127.0.1.1.

  • Local development

    Developers bind test services to different 127.x addresses to avoid port clashes.

Conflicts and gotchas

  • localhost inside a container. 127.0.0.1 inside a Docker container is the container itself, not the host. Use the host's bridge IP or host.docker.internal.
  • Binding to 127.0.0.1 in production. A service listening only on loopback can't be reached from other machines. Bind to the real interface (or 0.0.0.0) when it needs to be.
  • Blocking all of 127/8. Firewall rules that only allow 127.0.0.1 can break software using 127.0.0.53 or 127.0.1.1.

How to split 127.0.0.0/8

Worked example: into /16s

  1. Going from /8 to /16 borrows 16 − 8 = 8 bits from the host part.
  2. Each borrowed bit doubles the number of subnets: 28 = 256 subnets.
  3. Each /16 keeps 32 − 16 = 16 host bits: 216 = 65,536 addresses, so 65,534 usable after removing network and broadcast.
  4. The new mask is 255.255.0.0, so subnets step by 1 in the second octet: 127.0.0.0/16, 127.1.0.0/16, 127.2.0.0/16 … up to 127.255.0.0/16.
Ways to split 127.0.0.0/8
Split into Subnets Usable each First blocks Good for
/16 256 65,534 127.0.0.0/16, 127.1.0.0/16, … 256 /16s — only useful for local test setups.
/24 65,536 254 127.0.0.0/24, 127.0.1.0/24, … 65,536 /24s.

127.0.0.0/8 FAQ

Is 127.0.0.2 also localhost?

Yes. Every address in 127.0.0.0/8 is a loopback address on the local machine.

Can 127.0.0.0/8 be used on a network?

No. Loopback packets must never appear on a network; routers drop them.

What is the IPv6 equivalent of 127.0.0.1?

::1. IPv6 has a single loopback address, not a whole range.

Related tools

CIDR to IP Range Every address in 127.0.0.0/8 CIDR Calculator Split 127.0.0.0/8 into any size Subnet Overlap Checker Check it against your other ranges VLSM Calculator Split it into different-sized subnets /8 explained Mask, block size and maths for any /8

Other well-known networks: 10.0.0.0/24, 10.0.0.0/8, 100.64.0.0/10, 169.254.0.0/16, 172.16.0.0/12, 172.17.0.0/16, 192.168.0.0/16, 192.168.0.0/24, 192.168.1.0/24 · all networks