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Wednesday, July 28, 2010

Why loopback network 127.0.0.0?

Why do we need a whole network for loopback 127.0.0.0?

  • 127.0.0.1 is the standard IP address used for a loopback network connection. This means that if you try to connect to 127.0.0.1, you are immediately looped back to your own machine. 127.0.0.1 is also referred to as “localhost”, meaning ‘this computer’.127.0.0.0/8 - This block is assigned for use as the Internet host loopback address. A datagram sent by a higher level protocol to an address anywhere within this block should loop back inside the host.
  • Making a connection with a 127.0.0.1 loopback address is the same as making a connection with any remote computer on the network, but avoiding the local network interface hardware. It is widely used by application developers and system administrators with the intention of testing software/applications.
  • From RFC3330 - Special-Use IPv4 addresses -

  • 127.0.0.0/8 - This block is assigned for use as the Internet host
    loopback address. A datagram sent by a higher level protocol to an
    address anywhere within this block should loop back inside the host.
    This is ordinarily implemented using only 127.0.0.1/32 for loopback,
    but no addresses within this block should ever appear on any network
    anywhere [RFC1700, page 5].

  • In other words the whole of the 127.0.0.0/8 network is reserved for looping back to the host but it is general practice to only use 127.0.0.1.

Citation - This blog post does not reflect original content from the author. Rather it summarizes content that are relevant to the topic from different sources in the web. The sources might include any online discussion boards, forums, websites and others.

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