Don't Panic — IPv6

IPv6 is the Internet Protocol that moves packets between networks after IPv4 ran short of comfortably assignable addresses. It does the familiar IP job with a new packet format, a much larger address, and a few rules that refuse to behave like their older relative. The extra colons are not a personality test. They are hexadecimal groups trying to fit on a line.

The durable picture has three pieces. An address identifies an interface, while a prefix marks the leading bits that identify a block. Neighbor Discovery, the ICMPv6 local-link protocol, builds the map from a host to nearby routers and neighbors. Then a route chooses the next hop. If you keep those jobs separate, a surprising amount of IPv6 stops looking like decorative punctuation.

The surprising part is that IPv6 does not treat ICMPv6 as optional background noise. Router Advertisements tell hosts about routers and prefixes. Neighbor Discovery resolves a local next hop. Packet Too Big messages tell a source that a path cannot carry its current packet size. Block all of that and the network has removed several of its own signposts, which is a bold navigation strategy.

IPv6 also does not erase IPv4 overnight. Dual stack lets both protocols exist together, so DNS can return AAAA records for IPv6 and A records for IPv4. That means a working IPv4 connection does not certify the IPv6 route, filtering, address selection, or service. It merely proves that one of the two roads is paved.

For the full map, read the Intro to follow address formation, Neighbor Discovery, forwarding, and Path MTU behavior in order. Use the Slides when you need the relationships compressed into one packet-shaped mental model. Keep the Cheatsheet nearby for special prefixes, message roles, address states, and the troubleshooting sequence. The practice reference turns the theory into an isolated link where an on-link decision, a route, and a neighbor entry have nowhere to hide.

Don't Panic — IPv6

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