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Networking Fundamentals · Foundational

IPv6 Address Compression

Rules for shortening IPv6 addresses: omit leading zeros in each hextet and replace one longest run of all-zero hextets with ::.

Definition

The double colon may be used only once in an address, because using it twice would make the number of zeros ambiguous. RFC 5952 says to compress the longest run of zero hextets (the first if tied) and not to use :: for a single zero hextet. Trailing zeros in a hextet cannot be removed.

Example

2001:0db8:0000:0000:0000:0000:0000:0001 compresses to 2001:db8::1.

Exam tip

An address with two :: sequences is invalid; removing trailing zeros (db80 to db8) changes the address.

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