IPv6 Addressing Explained: Format, Types & Shortening
IPv6 uses 128-bit addresses (vs IPv4's 32) — enough for every device on Earth many times over. They're written as eight groups of four hex digits, and can be shortened by removing leading zeros and collapsing one run of all-zero groups with a double colon ::.
Shortening rules with an example
Take 2001:0db8:0000:0000:0000:ff00:0042:8329. Remove leading zeros in each group → 2001:db8:0:0:0:ff00:42:8329. Collapse the longest run of zero groups with :: → 2001:db8::ff00:42:8329. You may use :: only once per address (otherwise it's ambiguous). This shortening is a guaranteed CCNA question.
Address types
- Global unicast (2000::/3) — public, internet-routable.
- Link-local (FE80::/10) — auto-configured on every interface, used on the local link only.
- Unique local (FC00::/7) — private, like IPv4's RFC 1918 ranges.
- Multicast (FF00::/8) — one-to-many (IPv6 has no broadcast).
Frequently asked questions
How long is an IPv6 address?
128 bits, written as eight groups of four hexadecimal digits separated by colons.
How do you shorten an IPv6 address?
Remove leading zeros within each group and replace the longest single run of all-zero groups with a double colon (::), which may be used only once per address.
What is an IPv6 link-local address?
An FE80::/10 address auto-configured on every IPv6 interface, used only for communication on the local link (not routed).
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