What is IPV6 for localhost and 0.0.0.0?

As we all know that IPv4 address for localhost is 127.0.0.1 (loopback address).

Actually, any IPv4 address in 127.0.0.0/8 is a loopback address.

In IPv6, the direct analog of the loopback range is ::1/128. So ::1 (long form 0:0:0:0:0:0:0:1) is the one and only IPv6 loopback address.

While the hostname localhost will normally resolve to 127.0.0.1 or ::1, I have seen cases where someone has bound it to an IP address that is not a loopback address. This is a bit crazy … but sometimes people do it.

I say “this is crazy” because you are liable to break applications assumptions by doing this; e.g. an application may attempt to do a reverse lookup on the loopback IP and not get the expected result. In the worst case, an application may end up sending sensitive traffic over an insecure network by accident … though you probably need to make other mistakes as well to “achieve” that.

Blocking 0.0.0.0 makes no sense. In IPv4 it is never routed. The equivalent in IPv6 is the :: address (long form 0:0:0:0:0:0:0:0) … which is also never routed.

The 0.0.0.0 and :: addresses are reserved to mean “any address”. So, for example a program that is providing a web service may bind to 0.0.0.0 port 80 to accept HTTP connections via any of the host’s IPv4 addresses. These addresses are not valid as a source or destination address for an IP packet.

Finally, some comments were asking about ::/128 versus ::/0 versus ::.

What is this difference?

Strictly speaking, the first two are CIDR notation not IPv6 addresses. They are actually specifying a range of IP addresses. A CIDR consists of a IP address and an additional number that specifies the number of bits in a netmask. The two together specify a range of addresses; i.e. the set of addresses formed by ignoring the bits masked out of the given address.

So:

  • :: means just the IPv6 address 0:0:0:0:0:0:0:0
  • ::/128 means 0:0:0:0:0:0:0:0 with a netmask consisting of 128 bits. This gives a network range with exactly one address in it.
  • ::/0 means 0:0:0:0:0:0:0:0 with a netmask consisting of 0 bits. This gives a network range with 2128 addresses in it.; i.e. it is the entire IPv6 address space!

For more information, read the Wikipedia pages on IPv4 & IPv6 addresses, and CIDR notation:

Related Posts:

  1. How can I convert IPV6 address to IPV4 address?
  2. what does “dead beef” mean?
  3. What does it mean /64 in IPv6
  4. Do you need separate IPv4 and IPv6 listen directives in nginx?
  5. How can one distinguish the host and the port in an IPv6 URL?
  6. Can’t connect to MySQL server on ‘127.0.0.1’ (10061) (2003)
  7. Localhost is not working
  8. How do I kill the process currently using a port on localhost in Windows?
  9. wordpress on localhost lamp doesn’t let me install plugins
  10. Functions.php code that only runs on localhost?
  11. WordPress Subdomain MultiSite on localhost XAMPP on :8080 with IIS taking port 80
  12. WP Asking for FTP Credentials with XAMPP Localhost
  13. Testing local server with MAMP/wordpress on mobile device? [closed]
  14. How to automatically update on localhost after editing files
  15. error importing localhost export file to server
  16. wp_mail() is not working in localhost
  17. How to do a MySQL dump from production site without using a search and replace script for local development?
  18. Switching from editing on directly on remote server to PHPstorm local development?
  19. No wp-config.php file on local install of wordpress – site still displays
  20. Why does One Click Update fail on localhost using FTP with 777 permissions on site files?
  21. WordPress Admin Interface not styled properly
  22. WordPress Multisite local: wp-login.php refreshes on login Chrome Browser
  23. Error migrating from live website to localhost
  24. Why is ‘admin’ missing from my admin links?
  25. 403 Forbidden with gutenberg
  26. localhost on iPhone not loading images
  27. Import live site to local setup without access to live site
  28. “The package could not be installed” when updating plugins, themes, and core files on WampServer
  29. website is still in localhost
  30. Moving online website to MAMP or dumb idea?
  31. I have a desktop and a laptop: What’s the best way to move between local installations?
  32. How to migrate production WordPress to Localhost
  33. Problem moving my WordPress live site to localhost
  34. Multisite on localhost using xampp
  35. Connect to a remote database for wordpress in my own hosting server
  36. WordPress on a local machine redirecting to xampp dashboard page [closed]
  37. TTFB increased for no reason
  38. How to first edit in local WordPress editor on page and the add code?
  39. Cannot complete migration on LAMP
  40. WordPress php mysql errors – errcode: 13 permission denied
  41. How can I view wordpress site hosted locally in my home LAN network from the Internet (outside LAN network)?
  42. WordPress themes incomplete installation or installation problem
  43. Localhost port is missing on some links after downgrading MAMP [closed]
  44. Allowing WordPress from non-public address/domain
  45. Migrating to local server
  46. Redirect loop error on wordpress landing page on localhost
  47. Redirect to another page using contact form 7? [closed]
  48. Migrating Multisite with WP-Cli and/or Search-Replace-DB
  49. How to recover WordPress Adress(URL)
  50. can’t see aditional themes in control panel
  51. Local wordpress install only shows home page, all other pages Not Found
  52. Live to Local on MAMP, not working, outputting functions.php code
  53. Deploying Local WordPress Site
  54. change wordpress upload url to subdomain on xampp local
  55. How do I correctly configure my AMPPS localhost to use subdomains for multisite?
  56. Unable to install and upload theme due to php.ini file [closed]
  57. Row background image not showing in mobile browser served from wamp local host
  58. Where can I see MySQL hostname and port for wp-config.php
  59. Developing on localhost remove “index.php”
  60. Image Sizes/Thumbnails not generating on local install Ampps
  61. My wordpress site is using local ip to point to jquery and other files, how to fix it?
  62. How to replace permalinks
  63. Installing local to live WP into subdirectory
  64. Database migration issues – Error #1046 No database selected
  65. database not responding on localhost
  66. Need help changing back the correct wordpress url
  67. how to config the home page locally
  68. Only the most recent post is showing on my category page (working on localhost, not live site)
  69. How to install multiple wordpress site on localhost
  70. Clone WordPress for testing on localhost (with Fiddler)
  71. Unusual Apache2 Error Causing WordPress Redirect Error?
  72. How to re-connect WP files in lampp/htdocs to new SQL database to recover site under development
  73. When I save changes for css and js in my WP localhost env windows 10 the changes don’t take effects immediately!
  74. Uploading website to live causing problems to plug-in and layout
  75. Move wordpress files from one pc to another pc contents showing error
  76. WordPress can’t be reached on uWAMP when I change from port 80
  77. Page 404 Error on Localhost
  78. Woocommerce product page 404 not found
  79. WP 5-minute Install Error: “Waiting on Localhost…” —why does this happen?
  80. Local WordPress from Git repo, where to set document root?
  81. How to transfer /wordpress folder from one Mac to another
  82. Locally installing wordpress. Database problem
  83. Import WordPress site to localhost, but loads blank white screen [closed]
  84. Cloning wordpress intsall on mac
  85. Localhost WordPress Uploading of Images Issue
  86. Error on update translation
  87. Problems in migration of WordPress site from local server to the online server
  88. Merging separate works in wordpress
  89. wordpress home is gone
  90. Storing images on a local site
  91. Issues when moving from server to MAMP
  92. wordpress multisite duplicator plugin clon to localhost(xampp) but image not show
  93. wordpress login blank screen [closed]
  94. How to create a child theme without losing changes made to parent
  95. Where to store the images of a custom WordPress theme?
  96. Error Message when logging into WordPress on Xampp
  97. How do I upload my WordPress code files from previous website onto local host WordPress website?
  98. In my /etc/hosts/ file on Linux/OSX, how do I do a wildcard subdomain?
  99. How does IPv6 subnetting work and how does it differ from IPv4 subnetting?
  100. WordPress Localhost migration issue

Leave a Comment

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)