Transport Protocols Evolution or how to migrate your configuration today.#

Alex Mitev — Cisco

• Why: Practical, config-level RSVP-TE→SR migration guidance for WAN transport — complements the Arista overlay talk with the "how to actually move" side.
• What: Historical framing of RSVP-TE's scaling failure (headend 8k→32k and midpoint 64k→256k state growth, k·n² core state, no inter-domain) versus SR's state-in-the-packet model, then a use-case ladder: Ti-LFA for post-convergence-path FRR with 100% coverage and ECMP backups (replacing the hard-to-complete RSVP FRR configurations shown in full); microloop avoidance via segment-routing with RIB-update delay; Flex-Algo covering ~80% of transport intents with metric+constraints (delay, affinities, SRLG); explicit SR paths for the 5–10% needing strict/weighted SID lists; on-demand nexthop + automated steering (~95% of use); disjointness; guaranteed-bandwidth circuit-style policies with SDN-controller-managed reservation and QoS admission control; auto-bandwidth (RSVP-style behavior without midpoint state); tactical TE for congestion mitigation. Full IOS XR config snippets throughout, and an RFC reference set (8402, 8754, 8986, 9252, 9256, 9350, 9352, 9259, 9503, 9800).
• How: Config-first teaching: each ladder rung gets its problem statement, config, and a "share of use cases" estimate.
• Where applicable: Configs are Cisco IOS XR-specific; the concepts and RFCs are multi-vendor (and overlap with the Arista WAN-SR content). Most useful to operators with existing MPLS/RSVP estates planning incremental SR migration. Vendor-educational rather than a product pitch.