Count the LSPs a PE mesh needs, the label space they consume and the RSVP-TE refresh load they generate.
Because LSPs are unidirectional the full-mesh count is n(n − 1) rather than half that, and RSVP-TE keeps each one alive with periodic Path and Resv messages. The refresh figure is what turns LSP count into real control-plane load. RSVP-TE refresh is the term that limits TE deployments — a few thousand LSPs is fine, tens of thousands is a control-plane project, and it is the main reason Segment Routing removed per-LSP state from the core entirely.
MPLS LSP
A full PE mesh needs n(n − 1) unidirectional LSPs, since MPLS LSPs are one-way; hub and spoke needs 2 × spokes × hubs.
Soft-state refresh
RSVP refresh load = 2 × LSPs ÷ refresh interval messages per second.
A full PE mesh needs n(n − 1) unidirectional LSPs, since MPLS LSPs are one-way; hub and spoke needs 2 × spokes × hubs. Because LSPs are unidirectional the full-mesh count is n(n − 1) rather than half that, and RSVP-TE keeps each one alive with periodic Path and Resv messages. The refresh figure is what turns LSP count into real control-plane load.
RSVP-TE refresh is the term that limits TE deployments — a few thousand LSPs is fine, tens of thousands is a control-plane project, and it is the main reason Segment Routing removed per-LSP state from the core entirely.
This calculator takes 5 inputs: PE routers, Tunnel topology, Hub routers (hub-and-spoke only), Platform label space, RSVP refresh interval. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Refresh reduction (RFC 2961) bundles and acknowledges messages so state does not need constant retransmission, and summary refresh cuts the volume further. Segment Routing removes the problem outright by keeping path state only at the ingress.