OPERATIONAL DEFECT DATABASE
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For TI-MoFRR (Topology Independent Multicast-Only Fast ReRoute), if one path fails and data stops on the other path momentarily, traffic can be lost until the first path recovers, even though traffic is flowing on the alternate path.
This problem happens only when using static routes for the two RPF paths. The failure is basically a double-fault condition: a failure on one path, and then either a momentary failure on the remaining path, or a temporary stoppage of transmission from the source.
On "tail" routers, either unconfigure and reconfigure the (S,G) routes, or else trigger the control plane to reprogram the TI-MoFRR routes in the LCs: Clear PIM topology S G (Omit S G to clear all routes.) Even without the workaround, traffic will automatically recover as soon as the failed path is restored.
TI-MoFRR provides a means to provision two paths for multicast traffic, to provide fast re-route on failure. The "head" end duplicates the incoming traffic and changes the original IP source address to each of two fictitious "core" addresses. The two resulting streams take different paths through the core network. At "tail" or "bud" nodes the two streams are merged by selecting one to be forwarded to customers, replacing the original IP source address. The two paths (actually, trees) through the network can be configured using static routing for the two core IP source addresses, or using rpf-vector filtering. With static routing, when traffic loss happens on the second path, it switches over to the original path and wait for traffic to appear (which doesn't happen). Traffic reappearing on the second path is not noticed. In the rpf-vector case, the failed path will disappear, so this last switchover back to the failed path will not happen, avoiding the problem.
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