Cisco ASR 9000 Series Software Manual page 93

Implementing Layer-3 Multicast Routing on Cisco IOS XR Software
Faster convergence is obtainable in Flow-based MoFRR by monitoring the packet counts of the primary
stream. If no activity is detected for 30 ms, the switch over is triggered to the backup stream and the traffic
loss is within 50 ms.
Restrictions
These limitations apply to MoFRR deployments when the Cisco ASR 9000 Series SPA Interface Processor-700
linecard is used in the Cisco ASR 9000 Series Router chassis.
1 Cisco ASR 9000 Series SPA Interface Processor-700 cannot be used on ingress interface as either the
primary or backup (ECMP paths) path back to the multicast source.
2 The egress interfaces on Cisco ASR 9000 Series SPA Interface Processor-700 may lead to duplicate
multicast streams for short periods of time (the time between the switch from Trident primary to Trident
backup paths on ingress).
Non-ECMP MoFRR
TI (Topology-Independent) MoFRR is a multicast feature that performs fast convergence (Fast ReRoute) for
specified routes/flows when failure is detected on one of the paths between the router and the source.
Flow based non-ECMP approach uses a mechanism where two copies of the same multicast stream flow
through disjoint paths in the network. At the point in the network (usually the tail PE that is closer to the
receivers) where the two streams merge, one of the streams is accepted and forwarded on the downstream
links, while the other stream is discarded. When a failure is detected in the primary stream due to a link or
node failure in the network, MoFRR instructs the forwarding plane to start accepting packets from the backup
stream (which now becomes the primary stream).
For more information about topology independent MoFRR, refer the Cisco ASR 9000 Series Aggregation
Services Router Multicast Configuration Guide.
Implementing Non-ECMP MoFRR
The config handler in PIM creates a mapping between (S1, G) and (S2, G) in an internal mapping database.
No explicit route is created till a downstream join / data signal is received for (S1, G).
Downstream (S, G) join
The tail PE on receipt of (S, G) JOIN looks up the mapping database and,
• Creates the (S1, G) route entry with proxy info and marks it as primary mofrr route.
• Creates the (S2, G) route entry with the proxy info and marks it as backup mofrr route.
• Creates reference to (S2, G) from (S1, G) route and vice versa.
• Redistributes route with MoFRR primary & backup flags to PD.
Downstream (S,G) prune
The tail PE on receipt of (S, G) PRUNE looks up the mapping database and,
• ◦ Deletes the (S1, G) route entry with proxy info and redistributes the route delete.
◦ Deletes the (S2, G) route entry with proxy info and redistributes the route delete.
Cisco ASR 9000 Series Aggregation Services Router Multicast Configuration Guide, Release 5.1.x
Non-ECMP MoFRR
93