Virtual Private Routed Network Services
7750 SR OS Services Guide Page 1117
Configuring Overload State on a Single SFM
A 7x50 system with a single SFM installed has a system multicast throughput that is only a half of
a 7x50 system with dual SFMs installed. For example, in a mixed environment in which IOM1s,
IOM2s, and IOM3s are installed in the same system (chassis mode B or C), system multicast
throughput doubles when redundant SFMs are used instead of a single SFM. If the required
system multicast throughput is between 16G and 32G (which means both SFMs are being actively
used), when there is an SFM failure, multicast traffic needs to be rerouted around the node.
Some scenarios include:
• There is only one SFM installed in the system
• One SFM (active or standby) failed in a dual SFM configuration
• The system is in the ISSU process
You can use an overload state in IGP to trigger the traffic reroute by setting the overload bit in IS-
IS or setting the metric to maximum in OSPF. Since PIM uses IGP to find out the upstream router,
a next-hop change in IGP will cause PIM to join the new path and prune the old path, which
effectively reroutes the multicast traffic downstream. When the problem is resolved, the overload
condition is cleared, which will cause the traffic to be routed back to the router.
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