BGP Next Hop Dependent Characteristics Attribute#

John Scudder (Juniper) presenting the split of draft-ietf-idr-entropy-label

• Why: NHC is the base container for per-next-hop forwarding-plane signaling in BGP — three other WG drafts (next-next-hop-nodes, iFIT capabilities, generic metric) now define their own NHC characteristics on top of it. The session resolves a two-year stall that was blocking them.
• What: The NHC attribute — a transitive BGP attribute, extensible via TLVs, that conveys characteristics of the routes advertised in the UPDATE that carries it (unlike RFC 5492 capabilities). News at IETF 124: the parked draft-ietf-idr-entropy-label (WGLC'd November 2023, stuck "waiting for implementation") was split into draft-ietf-idr-nhc (the attribute plus a BGP Identifier characteristic) and draft-ietf-idr-elc (the Entropy Label Characteristic) — "nothing added or taken away."
• How: Two implementations of NHC exist; the split (chairs' consensus call, no objections) separates the twice-implemented base from ELC, which still awaits a second implementation, and unblocks the registry the dependent drafts need. Next steps: update the implementation report, reconfirm WGLC, publish.
• Where applicable: Any BGP deployment signaling datapath capabilities of next hops (entropy labels, GLB tuples, iFIT, metrics). Mature WG item now moving to publication; the plumbing beneath the NNHN/GLB work above.