Use /127 only on inter-router point-to-point IPv6 links

Use this document to resolve one bounded operational decision: Use /127 only on inter-router point-to-point IPv6 links. Only the official source and traced locations below supply facts. Confirm applicability before acting.

Source fact:

The official RFC 6164 — Using 127-Bit IPv6 Prefixes on Inter-Router Links from RFC Editor / Internet Engineering Task Force supports the following bounded statements:

• The /127 recommendation applies only to point-to-point links with exactly two routers and no attached hosts; router-to-host and mixed links are outside its scope. The research record locates this support at Section 2 (Scope of This Memo).
• A /127 removes the unused on-link address range that otherwise permits ping-pong forwarding or mass creation of unresolved neighbor-cache entries. The research record locates this support at Sections 5.1 (Ping-Pong Issue) and 5.2 (Neighbor Cache Exhaustion Issue).
• Routers must support /127 on inter-router point-to-point links and must disable Subnet-Router anycast for a prefix used that way. The research record locates this support at Section 6 (Recommendations).

Do not import neighboring assumptions into the source record. The supported task is a scoped comparison involving address plans, interfaces, routes, peers, protocol roles, timers, middleboxes, and intended failure domains and the conditions the source actually describes.

What the source does not establish

This RFC evidence supports only the named network-protocol decision; it does not select vendor settings, topology, capacity, or an acceptable failure mode. A correct source interpretation can still be inapplicable to a particular design. Confirm DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring, ownership, and change authority instead of treating documented behavior as a deployment guarantee.

Applicability questions

• For source statement 1 at Section 2 (Scope of This Memo), which observable configuration, record, or test can confirm applicability here?
• For source statement 2 at Sections 5.1 (Ping-Pong Issue) and 5.2 (Neighbor Cache Exhaustion Issue), which observable configuration, record, or test can confirm applicability here?
• For source statement 3 at Section 6 (Recommendations), which observable configuration, record, or test can confirm applicability here?
• Within address plans, interfaces, routes, peers, protocol roles, timers, middleboxes, and intended failure domains, which versions, roles, and configuration states define the review population?
• Could DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring invalidate the test, hide a failure, or change applicability?
• Who owns the decision, and which observation requires stopping, escalation, or rollback?

DSE recommendation:

DSE recommends using the cited source as the evidence anchor for this decision. Use a two-person review for the source interpretation and the resulting operational decision. Record the source location, examined part of address plans, interfaces, routes, peers, protocol roles, timers, middleboxes, and intended failure domains, observed and expected states, owner, and reason for deviation.

Do not move from citation to production in one step. Pilot the decision where practical, observe agreed signals, retain a reversal point, and verify DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring. Handle credentials, keys, recovery data, and personal information through approved secure channels.

Verification and evidence

Tie each conclusion back to Section 2 (Scope of This Memo); Sections 5.1 (Ping-Pong Issue) and 5.2 (Neighbor Cache Exhaustion Issue); Section 6 (Recommendations) and to observable material such as configuration snapshots, route or neighbor state, packet captures, counters, topology records, and controlled failover results. Preserve provenance and stable identifiers without copying secrets into the evidence set.

Close the review only when the evidence, exception handling, resulting action, and after-state are linked. Schedule a new review after material technical, organizational, incident, or source changes; today’s observation is not a continuing guarantee.

Official references

• RFC 6164 — Using 127-Bit IPv6 Prefixes on Inter-Router Links — RFC Editor / Internet Engineering Task Force