Is 1.1.1.1 a valid ip address

The message "Invalid IP Address" indicates a problem with your computer's network setup. Every computer that uses an Ethernet-type network, such as the Internet, has an Internet Protocol address that lets other computers communicate with it. Without a valid IP address your computer cannot use the network. A variety of reasons can make an IP address invalid, such as address conflicts with other computers and network configuration problems.

Description

1. An IP address is a set of numbers that identify your computer on a network. IPV4, the traditional numbering scheme, uses four integers ranging from zero to 255 and set apart by periods. For example, "204.120.0.15" is a valid IPV4 address. A newer IPV6 scheme, designed to eventually replace IPV4, uses a larger, more complex set of numbers mixed with other characters, such as letters.

Reserved Addresses

1. Networks set aside certain combinations for housekeeping and testing, such as the extreme values, "0.0.0.0" and "255.255.255.255." Another number, "127.0.0.1" is called the "localhost;" every computer on a network refers to itself as this address. Because these numbers have special meanings, the network does not assign them to PCs; such addresses would be invalid.

Address Conflicts

1. On a given network, every IP address must be unique. For example, two computers cannot both have the address "192.168.0.110." Although the address itself is valid, attempting to assign the same number to two machines creates a conflict and generates an error message.

Address Range Problems

1. Local networks, such as those used in schools, homes and offices, have a restricted range of addresses determined by the network administrator or the factory default settings of the network router. For example, a home office network might use addresses in the range of 192.168.1.1 to 192.168.1.50. The address "101.5.40.1" is out of the network's range and would be an invalid address.

DHCP Assignment Problems

1. A network service called Dynamic Host Configuration Protocol offers a convenient way to automatically assign IP addresses to computers joining a network. For example, as you return home from work, your smartphone picks up the Wi-Fi signal from your home network and the network's DHCP service gives the phone an IP address. Sometimes, however, DHCP-generated addresses can cause problems. For example, Windows might assign your PC an address before your Internet router does. The address may be invalid if it conflicts with the network's address range.

As stated by Daniel B in his answer, the 1.1.1.1 address is currently assigned to APNIC labs (as it was when the question has been asked). However, until January 2010, the 1.0.0.0/8 network block, of which 1.1.1.1 is part, was unassigned and therefore (ab)used for local use in several cases.

Although the network block has been now assigned to APNIC (and addresses starting with 1. are now definitely in use), several old pieces of equipment persist in using 1.1.1.1 for local purposes, and perhaps in consequence of this, a small block of 256 IP addresses (1.1.1.0 to 1.1.1.255) has been reserved for research purposes by APNIC labs.

No route for the 1.1.1.0/24 prefix containing 1.1.1.1 has ever been announced on BGP (see https://stat.ripe.net/1.1.1.1#tabId=at-a-glance for details, in particular 1.1.1.1 was never globally visible as exact match in BGP by any of the RIS peers since beginning of 2004. No less-specific covering prefixes.), which means that the address has never been used for a publicly-facing service. This of course does not mean that this will never happen.

The fact that you can have a traceroute to 1.1.1.1 that responds with the gateway address can come from two sources:

• The gateway figures out that the address can't be routed because there is no route announcement for it, and therefore answers with an ICMP "unreachable" message -- however your traceroute should in this case display a specific marking (e.g. !H). I would say that this explanation is not very probable, because your gatweay will probably only forward packets to the next router.
• The 1.1.1.1 address is still used locally by some equipment (see below).

Among unofficial uses of the 1.1.1.1 address, or of an address block containing it:

• Some equipment from several manufacturers (including Cisco and ZyXel) is still using the 1.1.1.1 address for local purposes (for example, login portals for public WiFi connections, local management networks, etc.). You can perhaps see what the equipment is by going to https://1.1.1.1/ with your browser. Also check the address of your DHCP or DNS server to see if one of those is 1.1.1.1.
• Fastweb, an Italian ISP (but probably other providers too), was in the past assigning IPs in the 1.0.0.0/8 network to their customers, but since that network range became public, they switched to a more classic private IP range (10.0.0.0/8).

UPDATE (April 11th 2018) — As per Bob's comment to another message, there is now a public DNS service on 1.1.1.1. See also https://1.1.1.1/ for more information about what this is. So this address is now definitely off-limits for private use! (as it should always have been).

$ ping 1.1.1.1
PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
64 bytes from 1.1.1.1: icmp_req=1 ttl=57 time=4.67 ms
64 bytes from 1.1.1.1: icmp_req=2 ttl=57 time=4.20 ms
64 bytes from 1.1.1.1: icmp_req=3 ttl=57 time=4.19 ms
64 bytes from 1.1.1.1: icmp_req=4 ttl=57 time=4.17 ms
^C
--- 1.1.1.1 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3030ms
rtt min/avg/max/mdev = 4.179/4.313/4.677/0.210 ms

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