What is the difference between 0 0 0 0 127 0 0 1 and localhost

Question

I am using Jekyll and Vagrant on my mac  I found that Jekyll server will bind to 0 0 0 0 4000 instead of 127 0 0 1 4000  Also gem server will bind to this address by default  I can still visit it via http   localhost port  But for Jekyll  it seems that the default setting  e g  0 0 0 0 4000  requires Internet access  I cannot run Jekyll server without Internet  Is it a  small bug   I also use Vagrant  I have set port forwarding 8080    4000  in Vagrantfile  since I install Jekyll in Vagrant virtual machine and test it under Macintosh  If I use the default setting  0 0 0 0 4000   it works  I can visit it from my safari with http   localhost 8080  But if there is not internet  I cannot bind to 0 0 0 0 4000  I use jekyll server -H 127 0 0 1 to bind service to 127 0 0 1 4000 instead  then I cannot visit it via http   localhost 8080   Can anyone explain the difference between 0 0 0 0  127 0 0 1 and localhost  And can anyone explain why the difference will cause this problem

User · Answer

In current version of Jekyll  it defaults to http   127 0 0 1 4000   This is good  if you are connected to a network but do not want anyone else to access your application     However it may happen that you want to see how your application runs on a mobile or from some other laptop computer    In that case  you can use  jekyll serve --host 0 0 0 0   This binds your application to the host  amp  next use  following to connect to it from some other host  http   host s IP adress 4000

User · Answer

127 0 0 1 is normally the IP address assigned to the  loopback  or local-only interface   This is a  fake  network adapter that can only communicate within the same host   It s often used when you want a network-capable application to only serve clients on the same host   A process that is listening on 127 0 0 1 for connections will only receive local connections on that socket    localhost  is normally the hostname for the 127 0 0 1 IP address   It s usually set in  etc hosts  or the Windows equivalent named  hosts  somewhere under  WINDIR    You can use it just like any other hostname - try  ping localhost  to see how it resolves to 127 0 0 1   0 0 0 0 has a couple of different meanings  but in this context  when a server is told to listen on 0 0 0 0 that means  listen on every available network interface    The loopback adapter with IP address 127 0 0 1 from the perspective of the server process looks just like any other network adapter on the machine  so a server told to listen on 0 0 0 0 will accept connections on that interface too   That hopefully answers the IP side of your question   I m not familiar with Jekyll or Vagrant  but I m guessing that your port forwarding 8080   gt  4000 is somehow bound to a particular network adapter  so it isn t in the path when you connect locally to 127 0 0 1

[ip] What is the difference between 0.0.0.0, 127.0.0.1 and localhost?

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