Negotiate Add-Path before advertising multiple paths for one prefix

Frame this document as a source-led configuration and assurance check: Negotiate Add-Path before advertising multiple paths for one prefix. Only the official source and traced locations below supply facts. Confirm applicability before acting.

Source fact:

The official RFC 7911 — Advertisement of Multiple Paths in BGP from RFC Editor / Internet Engineering Task Force supports the following bounded statements:

• The ADD-PATH capability declares, separately for each AFI/SAFI, whether the sender can receive paths, send paths, or do both. The research record locates this support at Section 4 (ADD-PATH Capability).
• A speaker may send multiple paths for an AFI/SAFI only when it advertised send capability and its peer advertised receive capability for that same AFI/SAFI. The research record locates this support at Section 5 (Operation), capability negotiation rule.
• The sender assigns a path identifier so prefix plus identifier uniquely selects one advertised path; a receiver must not infer semantics from that local identifier. The research record locates this support at Section 2 (How to Identify a Path).

These statements are the factual basis for this document. Do not extend them into a broader assurance. Review address plans, interfaces, routes, peers, protocol roles, timers, middleboxes, and intended failure domains only where the source and recorded environment align.

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 4 (ADD-PATH Capability), which observable configuration, record, or test can confirm applicability here?
• For source statement 2 at Section 5 (Operation), capability negotiation rule, which observable configuration, record, or test can confirm applicability here?
• For source statement 3 at Section 2 (How to Identify a Path), 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. Start with applicability, then compare the observed state with the cited source. 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.

If the review warrants change, use a bounded implementation with prerequisites, test population, monitoring, abort criteria, and a rehearsed reversal. Sequence checks for DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring and sanitize protected material before retention.

Verification and evidence

Evidence should let another reviewer reproduce this decision. Retain observations beside the traced locations Section 4 (ADD-PATH Capability); Section 5 (Operation), capability negotiation rule; Section 2 (How to Identify a Path). Favor configuration snapshots, route or neighbor state, packet captures, counters, topology records, and controlled failover results, linked to stable identifiers, time, and operator.

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 7911 — Advertisement of Multiple Paths in BGP — RFC Editor / Internet Engineering Task Force