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RFC 5952 / WRITE IPv6 ADDRESSES

Keep ports and prefixes separate

05

Brackets separate an IPv6 literal from a port; a slash introduces a prefix length. Text normalization does not prove identity or connectivity.

DIAGRAMRead RFC section 6 ↗
RFC 5952 · § 6EXAMPLE
5 / 5
Keep ports and prefixes separateSeparate contexts distinguish the legitimate address 2001:db8::1:80 from bracketed host 2001:db8::1 and port 80; show URI http://[2001:db8::1]:80/; normalize documentation prefix 2001:db8::/32 without changing 32; and compare two spellings as equal values without claiming trust or reachability. Boxes delimit literal and port fields. No URI is fetched.Separate surrounding-syntax examplesA: 2001:0DB8:0:0:0:0:0:1B: 2001:db8::1Parse · compare 128-bit valuesequal address valuesEquality does not prove identityStill check application authorizationNo certificate or reachability proof
05
Separate equality from trust.

Two legitimate spellings can compare as the same address after parsing. This does not prove a certificate, an allowed destination, or a reachable host.

Source for this drawing: RFC 5952 · Read RFC section 6 ↗

Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
New to this? Start hereA quick picture + helpful background

A message needs an address.

Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.

Helpful first, if these ideas are unfamiliar

RFC 8200 IPv6 RFC 3986 URI syntax

These pictures are analogies to help you learn. The linked RFC explains the actual rules.

Related RFCs and changes

“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.

KEY POINT

Preserve the surrounding syntax and the address value.

  • An unbracketed address:port is NOT RECOMMENDED because colons already occur inside IPv6 addresses. Bracketed [address]:port SHOULD be used by default unless otherwise specified.
  • URI IPv6 literals MUST follow RFC 3986 syntax: square brackets enclose the literal. RFC 5952 address rules apply within those brackets.
  • Text prefixes use the same representation method as addresses. The decimal /length counts leftmost prefix bits; canonicalizing text does not clear host bits or verify a network allocation.
DETAILS

RFC 5952 does not define URL authorization or certificate identity checks. Parse and compare address values where appropriate, then perform the application’s actual security checks. A canonical string does not establish that the destination exists. Verified editorial erratum 2498 corrects the explanation to colon usage; no technical requirement changes.

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