Auto-bandwidth for Segment Routing#

Dmytro Shypovalov – Vegvisir Systems

• Why: The missing RSVP-TE auto-bandwidth equivalent for SR is a real ISP pain; this is a working, open-source, standards-based design with honest production caveats.
• What: The problem: SR LSPs are stateless and most routers can't advertise per-LSP traffic rate (RFC 8733/RFC 9857 exist but require router-side sampling). The solution: an external bandwidth sampler (open source: github.com/Vegvisir-Systems/srte-sampler) collects SR LSP counters via gNMI and advertises the traffic rate to the PCE as a BGP-LS type-5 route with bandwidth TLV; the PCE recomputes segment lists and pushes via BGP-SRTE. Works today with IOS-XR, JunOS, EOS. PCE redundancy needs no state sync (distinct SRTE distinguishers, like route reflectors); total PCE failure falls back to IGP shortest path. The critique is self-aware: this merely replicates RSVP-TE auto-bandwidth; the better future design has the PCE query raw counters from existing telemetry (Telegraf/VictoriaMetrics) for a centralized traffic-matrix view, burst reaction, and analytics.
• How: Feedback loop: router counters → sampler → BGP-LS to PCE → updated segment list (BGP-SRTE preferred; PCEP explicitly discouraged). Mesh templates plus ACTN (RFC 8453) sketch the intent-based layer above it.
• Where applicable: Multi-vendor ISP SR-MPLS/SRv6 WANs; the author is candid about what "production-ready" requires (deterministic sampling, cross-controller identical results).