Published On: August 10ᵗʰ, 2021 02:10

IP Multicast Routing Configuration Guide, Cisco IOS XE Amsterdam 17.3.x (Catalyst 9500 Switches)

Contents

Prerequisites for Multicast Subsecond Convergence

Service providers must have a multicast-enabled core in order to use the Cisco Multicast Subsecond Convergence feature.

Restrictions for Multicast Subsecond Convergence

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.

Information About Multicast Subsecond Convergence

Benefits of Multicast Subsecond Convergence

  • 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.

Multicast Subsecond Convergence Scalability Enhancements

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

PIM Router Query Messages

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.

Reverse Path Forwarding

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.

Topology Changes and Multicast Routing Recovery

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.

How to Configure Multicast Subsecond Convergence

Modifying the PIM Router Query Message Interval

Perform this task to modify the PIM router query message interval.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type slot / subslot / port
  4. ip pim query-interval period [msec ]

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface type slot / subslot / port

Example:


Device(config)# interface gigabitethernet 1/0/0

Specifies the interface and enters interface configuration mode.

Step 4

ip pim query-interval period [msec ]

Example:


Device(config-if)# ip pim query-interval 45

Configures the frequency at which multicast routers send PIM router query messages.

Verifying Multicast Subsecond Convergence Configurations

Perform this task to display detailed information about and to verify information regarding the Multicast Subsecond Convergence feature.

SUMMARY STEPS

  1. enable
  2. show ip pim interface type number
  3. show ip pim neighbor

DETAILED STEPS

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

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:

Device# show ip pim interface GigabitEthernet 1/0/0
Address          Interface                Ver/   Nbr    Query  DR     DR
                                          Mode   Count  Intvl  Prior
172.16.1.4       GigabitEthernet1/0/0     v2/S   1      100 ms 1      172.16.1.4

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:

Device# show ip pim neighbor
PIM Neighbor Table
Neighbor          Interface                Uptime/Expires    Ver   DR
Address                                                            Prio/Mode
172.16.1.3        GigabitEthernet1/0/0     00:03:41/250 msec v2    1 / S

Configuration Examples for Multicast Subsecond Convergence

Modifying the PIM Router Query Message Interval Example

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

Additional References for IP Multicast Optimization: Multicast Subsecond Convergence

Related Documents

Related Topic

Document Title

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 9500 Series Switches)

Feature History for IP Multicast Optimization Multicast Subsecond Convergence

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

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).

Support for this feature was introduced only on the C9500-12Q, C9500-16X, C9500-24Q, C9500-40X models of the Cisco Catalyst 9500 Series Switches.

Cisco IOS XE Fuji 16.8.1a

IP Multicast Optimization: Multicast Subsecond Convergence

Support for this feature was introduced on the C9500-32C, C9500-32QC, C9500-48Y4C, and C9500-24Y4C models of the Cisco Catalyst 9500 Series Switches.

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/