Advertise OSPF maximum metrics when a router must remain non-transit

Frame this document as a source-led configuration and assurance check: Advertise OSPF maximum metrics when a router must remain non-transit. Only the official source and traced locations below supply facts. Confirm applicability before acting.

Source fact:

The official RFC 6987 — OSPF Stub Router Advertisement from RFC Editor / Internet Engineering Task Force supports the following bounded statements:

• An OSPF router that must remain reachable but avoid transit advertises MaxLinkMetric on every non-stub link in its router-LSA. The research record locates this support at Section 2 (Solutions).
• MaxLinkMetric is the 16-bit all-ones value 0xffff and signals that the advertised link should not carry transit traffic. The research record locates this support at Section 3 (Maximum Link Metric).
• Unlike clearing the OSPF R-bit, MaxLinkMetric can leave the router usable as transit when it is the only remaining path. The research record locates this support at Section 4 (Deployment Considerations).

Only the traced statements above are asserted as source facts. Apply the review to address plans, interfaces, routes, peers, protocol roles, timers, middleboxes, and intended failure domains after confirming that the source and deployed context match.

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. Do not read the source as proof of implementation or permission to change production. Its guidance remains conditional on DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring and the environment’s recorded constraints.

Applicability questions

• For source statement 1 at Section 2 (Solutions), which observable configuration, record, or test can confirm applicability here?
• For source statement 2 at Section 3 (Maximum Link Metric), which observable configuration, record, or test can confirm applicability here?
• For source statement 3 at Section 4 (Deployment Considerations), 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. Begin by recording scope and current state before deciding whether a change is warranted. 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.

For an approved change, define prerequisites, a limited test path, success and stop conditions, monitoring, and rollback. Check DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring in design order. Protect credentials, keys, recovery material, personal data, and sensitive topology in evidence.

Verification and evidence

Build a reproducible chain from Section 2 (Solutions); Section 3 (Maximum Link Metric); Section 4 (Deployment Considerations) to the observed environment. Useful domain evidence includes configuration snapshots, route or neighbor state, packet captures, counters, topology records, and controlled failover results; label every item with scope, timestamp, collector, and stable identifier.

Retain the starting state, authorization, execution record, outcome, deviation, and final state as one review package. Move disruptive checks to an approved test path. Reopen the decision when versions, design, dependencies, ownership, or official guidance changes.

Official references

• RFC 6987 — OSPF Stub Router Advertisement — RFC Editor / Internet Engineering Task Force