Disable Subnet-Router anycast for this prefix
02Anycast delivers to one member of a set. The Subnet-Router anycast role is distinct from an ordinary interface address; its historical conflict explains an essential /127 requirement.
Separate document-history view: RFC 6547 moved RFC 3627 to Historic and obsoleted it. It updates RFC 6164; it does not make RFC 6164 an Internet Standard or a blanket replacement for all addressing rules.
Source for this drawing: RFC 6164 · Read RFC section 6 ↗
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
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
RFC 6547 obsoletes RFC 3627, moves it to Historic status and updates RFC 6164 to make the newer guidance clear. RFC 6164 itself has no formal Obsoletes relationship in the official metadata.
Read the updated RFC section ↗RFC 4291 §2.6.1 defines Subnet-Router anycast as the link’s subnet prefix followed by zeros. On a /127, that form coincides with the lower endpoint of the pair.
- RFC 4291 §2.6.1 defines Subnet-Router anycast as the link’s subnet prefix followed by zeros. On a /127, that form coincides with the lower endpoint of the pair.
- Routers MUST disable Subnet-Router anycast for the prefix when /127 prefixes are used. This is not a command to disable every kind of anycast throughout a network.
- RFC 6547 §1 updates this publication’s history: it obsoletes RFC 3627 and moves that older discouragement to Historic. Follow RFC 6164 when the guidance conflicts. No formal updates/obsoletions beyond the official metadata are invented.
Fictional documentation addresses within 2001:db8::/32. Bounded operator-chosen address examples, not a complete router, Neighbor Discovery, ICMPv6 or address-validation implementation.
Read the RFC section ↗