Cisco Cisco IOS Software Release 12.0(22)S
Multicast Subsecond Convergence
Feature Overview
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Cisco IOS Release 12.0(22)S
Because PIM relies on the unicast routing table to calculate its Reverse Path Forwarding (RPF) when a
change in the network topology occurs, unicast protocols first need to calculate options for the best paths
for traffic, and then multicast can determine the best path.
change in the network topology occurs, unicast protocols first need to calculate options for the best paths
for traffic, and then multicast can determine the best path.
Multicast subsecond convergence allows multicast protocol calculations to finish almost immediately
after the unicast calculations are completed. As a result, multicast traffic forwarding is restored
substantially faster after a topology change.
after the unicast calculations are completed. As a result, multicast traffic forwarding is restored
substantially faster after a topology change.
The scalability enhancements improve on the efficiency of handling increases (or decreases) in service
users (receivers) and service load (sources or content). Scalability enhancements in this release include
the following:
users (receivers) and service load (sources or content). Scalability enhancements in this release include
the following:
•
Improved Internet Group Management Protocol (IGMP) and PIM state maintenance through new
timer management techniques
timer management techniques
•
Improved scaling of the Multicast Source Discovery Protocol (MSDP) Source-Active (SA) cache
The scalability enhancements provide the following benefits:
•
Increased potential PIM multicast route (mroute), IGMP, and MSDP SA cache state capacity
•
Decreased CPU usage
Multicast subsecond convergence provides the ability to trigger a check of RPF changes for mroute
states. This check is triggered by unicast routing changes. By performing a triggered RPF check, users
can set the periodic RPF check to a relatively high value (for example, 10 seconds) and still fail over
quickly.
states. This check is triggered by unicast routing changes. By performing a triggered RPF check, users
can set the periodic RPF check to a relatively high value (for example, 10 seconds) and still fail over
quickly.
The triggered RPF check enhancement reduces the time needed for service to be restored after
disruption, such as for single service events (for example, in a situation with one source and one receiver)
or as the service scales along any parameter (for example, many sources, many receivers, and many
interfaces). This enhancement decreases in time-to-converge PIM (mroute), IGMP, and MSDP (SA
cache) states.
disruption, such as for single service events (for example, in a situation with one source and one receiver)
or as the service scales along any parameter (for example, many sources, many receivers, and many
interfaces). This enhancement decreases in time-to-converge PIM (mroute), IGMP, and MSDP (SA
cache) states.
Benefits
•
The scalability components improve on the efficiency of handling increases (or decreases) in service
users (receivers) and service load (sources or content).
users (receivers) and service load (sources or content).
•
New algorithms and processes (such as aggregated join messages, which deliver up to 1000
individual messages in a single packet) reduce the time to reach convergence by a factor of 10.
individual messages in a single packet) reduce the time to reach convergence by a factor of 10.
•
Multicast subsecond convergence improves service availability for large multicast networks.
•
Multicast users such as financial services firms and brokerages receive better quality of service,
because multicast functionality is restored in a fraction of the time previously required.
because multicast functionality is restored in a fraction of the time previously required.
Restrictions
Routers that use the subsecond DR failover enhancement need to be able to process hello interval
information arriving in milliseconds. Routers that are congested or do not have enough CPU cycles to
process the hello interval may assume that the PIM neighbor has gone, although this may not be the case.
information arriving in milliseconds. Routers that are congested or do not have enough CPU cycles to
process the hello interval may assume that the PIM neighbor has gone, although this may not be the case.