Prerequisites for Multicast Subsecond Convergence
Service providers must have a multicast-enabled core in order to use the Cisco Multicast Subsecond Convergence feature.
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Service providers must have a multicast-enabled core in order to use the Cisco Multicast Subsecond Convergence feature.
Devices that use the subsecond designated router (DR) failover enhancement must be able to process hello interval information arriving in milliseconds. Devices that are congested or do not have enough CPU cycles to process the hello interval can assume that the Protocol Independent Multicast (PIM) neighbor is disconnected, although this may not be the case.
The scalability components improve on the efficiency of handling increases (or decreases) in service 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.
Multicast subsecond convergence improves service availability for large multicast networks.
Multicast users such as financial services firms and brokerages receive better quality of service (QoS), because multicast functionality is restored in a fraction of the time previously required.
The Multicast Subsecond Convergence feature provides scalability enhancements that 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:
Improved Internet Group Management Protocol (IGMP) and PIM state maintenance through new 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 allows you to send PIM router query messages (PIM hellos) every few milliseconds. The PIM hello message is used to locate neighboring PIM devices. Before the introduction of this feature, the device could send the PIM hellos only every few seconds. By enabling a device to send PIM hello messages more often, this feature allows the device to discover unresponsive neighbors more quickly. As a result, the device can implement failover or recovery procedures more efficiently.
Unicast Reverse Path Forwarding (RPF) helps to mitigate problems caused by the introduction of malformed or forged IP source addresses into a network by discarding IP packets that lack a verifiable IP source address. Malformed or forged source addresses can indicate denial-of-service (DoS) attacks based on source IP address spoofing.
RPF uses access control lists (ACLs) in determining whether to drop or forward data packets that have malformed or forged IP source addresses. An option in the ACL commands allows system administrators to log information about dropped or forwarded packets. Logging information about forged packets can help in uncovering information about possible network attacks.
Per-interface statistics can help system administrators quickly discover the interface serving as the entry point for an attack on the network.
The Multicast Subsecond Convergence feature set enhances both enterprise and service provider network backbones by providing almost instantaneous recovery of multicast paths after unicast routing recovery.
Because PIM relies on the unicast routing table to calculate its 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.
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.
Perform this task to modify the PIM router query message interval.
Command or Action | Purpose | |
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Step 1 |
enable Example:
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Enables privileged EXEC mode.
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Step 2 |
configure terminal Example:
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Enters global configuration mode. |
Step 3 |
interface type slot / subslot / port Example:
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Specifies the interface and enters interface configuration mode. |
Step 4 |
ip pim query-interval period [msec ] Example:
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Configures the frequency at which multicast routers send PIM router query messages. |
Perform this task to display detailed information about and to verify information regarding the Multicast Subsecond Convergence feature.
Step 1 |
enable Example:
Enables privileged EXEC mode.
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Step 2 |
show ip pim interface type number Use this command to display information about interfaces configured for PIM. The following is sample output from the show ip pim interface command: Example:
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Step 3 |
show ip pim neighbor Use this command to display the PIM neighbors discovered by the Cisco IOS XE software. The following is sample output from the show ip pim neighbor command: Example:
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In the following example, the ip pim query-interval command has been set to 100 milliseconds. This command does not show up in show running-config command output unless the interval value has been configured to be the nondefault value.
!
interface gigabitethernet 1/0/1
ip address 172.16.2.1 255.255.255.0
ip pim query-interval 100 msec
ip pim sparse-mode
Related Topic |
Document Title |
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For complete syntax and usage information for the commands used in this chapter. |
See the IP Multicast Routing Commands section of the Command Reference (Catalyst 9300 Series Switches) |
This table provides release and related information for the features explained in this module.
These features are available in all the releases subsequent to the one they were introduced in, unless noted otherwise.
Release |
Feature |
Feature Information |
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Cisco IOS XE Everest 16.5.1a |
IP Multicast Optimization: Multicast Subsecond Convergence |
The Multicast Subsecond Convergence feature provides scalability enhancements that improve on the efficiency of handling increases (or decreases) in service users (receivers) and service load (sources or content). |
Use the Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to https://cfnng.cisco.com/