IPv6 notation guide
IPv6 compression makes a 128-bit address shorter to read and write without changing its value. The rules are precise: remove leading zeroes, abbreviate one eligible zero run, and use lowercase hexadecimal text.
Rule one
An IPv6 address has eight groups of four hexadecimal digits in expanded form. Within each group, leading zeroes have no value and can be omitted. Keep at least one digit when a group contains only zeroes.
Expanded group
0db8
Compressed group
db8
Rule two
A sequence of two or more complete 0000 groups can be replaced with a double colon. Use this abbreviation only once in one address; otherwise it would be ambiguous how many zero groups are missing.
If multiple zero sequences have the same length, use the first sequence. A single zero group is written as 0, not ::.
Worked examples
2001:0db8:0000:0000:0000:0000:0000:0001
→2001:db8::1
Leading zeroes removed; five zero groups collapsed.
fe80:0000:0000:0000:0202:b3ff:fe1e:8329
→fe80::202:b3ff:fe1e:8329
Three zero groups collapsed; 0202 becomes 202.
2001:0db8:0000:0001:0000:0000:0000:0001
→2001:db8:0:1::1
The longest three-group zero run is collapsed.
Reference addresses
These selected addresses have dedicated context and can be safely used as examples when learning IPv6 notation.
Standard notation
A consistent compressed form prevents duplicate values in configuration, logs, databases, and URLs. It also makes troubleshooting easier because equivalent addresses are displayed the same way.