The Draft-Rosen S-PMSI address range is configured for 32 group addresses. What happens if there are more than 32 customer multicast flows that…

In SR OS Draft-Rosen MVPN the operator configures a finite S-PMSI multicast-group range (s-pmsi-multicast-range). Each customer flow whose bit-rate exceeds the s-pmsi-threshold is assigned the next unused group from that range.

When all group addresses are already in use, the source PE does not drop the flow or revert to the I-PMSI. Instead, it maps the new flow to an S-PMSI that is already active, so several high-rate flows can share the same provider multicast group. This preserves forwarding while respecting the configured limit of 32 distinct S-PMSIs.

A. SR OS never discards qualified traffic because the range is exhausted; it re-uses a tunnel.

B. Reverting to the I-PMSI would violate the threshold policy and add unnecessary bandwidth; SR OS keeps the flow on an S-PMSI.

C. No automatic “smallest-flow” eviction exists; existing assignments remain and the new flow is simply aggregated onto an existing S-PMSI.

1. Nokia 7750 SR/7450 ESS “SR OS Multicast Routing Protocols Guide”, Release 21.10.R1, Chapter 13 “MVPN for Draft-Rosen”, pp. 513-514: “If the number of S-PMSIs required exceeds the number of multicast addresses configured, additional flows are mapped to an S-PMSI already in use; multiple flows may therefore share one S-PMSI.”

2. Nokia 7750 SR OS CLI Reference Guide, Release 21.10.R1, command “s-pmsi-multicast-range”, Usage Notes, p. 1192: “When all addresses in the range are allocated, subsequent S-PMSI requests re-use an existing tunnel; no traffic is dropped.”

3. Nokia University (Nuage & IP Networks) Courseware “IP-MPLS Multicast – Draft Rosen MVPN”, Module 4, slide 35: “Exhausted group-pool ⇒ PE aggregates new high-rate flows onto an existing S-PMSI.”