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From my understanding, all IP addresses of the form 127.x.y.z are loopback addresses. Now that seems to be quite a waste to me; indeed, already more than one address seems like a waste.

Is there any use in having so many loopback addresses?

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1 Answer 1

up vote 6 down vote accepted

Some reasons I've found:

  1. Historical limitation: there is no MASK in the first implementation of tcpip, that means network nodes use the first number to distinguish network size and host ID. moreover, since class A is determined by its first octet, the higher-order bit is 0, so 127.x.x.x (01111111.x.x.x) is the latest segement of class A addresses. people often use all zero or all one numbers for special usages, reserving a class A segment is for maximum flexibility.

  2. Easy implementation: as what i say above, there was no MASK concept in early days, segment address 01111111.00000000.00000000.00000000 is easy to be determined by AND/XOR operations quickly and easily. even nowadays, such pattern is still easy for matching subnets by applying XOR operation.

  3. Reserved for future use: class A has 1,677,216 hosts, so it allows people have more space to divide it into a lot of reasonable zones for specific usages, different devices, systems and applications.

Extracted from here

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