IPv6 shortening and compressing address rules

An IPv6 address can be very long as it is a 128 bits one. Asking someone verbally to check the connectivity to a given address can be tricky :-)

There are however some rules to shorten it and it’s a way to remove zeros.

Rule 1: Suppress leading zeros

Remove all leading zeros, the left side zeros, in every 16 bits field.

For example:


will be simplified to


Of course 0000 becomes 0.

Rules 2: The larger sequence of :0:0: can be reduced to ::

You can compact a sequence of zeros to the symbol ::.

Applying the rule to 2001:db8:0:0:0:0:0:1 would get us 2001:db8::1.

  • You can’t compact just one :0: – only a sequence.
  • If there is more than one sequence of :0: you can only compact the large one. If they have the same length compact the first one.

2001:db8::1:1:1:1:1 is not correct. It must be 2001:db8:0:1:1:1:1:1.

2001:0:0:1:0:0:0:1 will become 2001:0:0:1::1.

2001:db8:0:0:1:0:0:1 will become 2001:db8::1:0:0:1.

That’s it.

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