Introduction
This documents lists various Multicast Configuration best practices in Catalyst 6500
Requirements
There are no specific requirements for this document.
Multicast configuration best practise
- To avoid processing multicast traffic in software:
- Ensure that the IIF and OIF MTU sizes match.
- Ensure that multicast sources are configured not to send multicast data packets with any IP options.
- Do not configure more than 4 bidirectional PIM rendezvous points (RPs) per VPN.
- With multiple multicast routing protocols configured (for example, sparse mode (SM) and Bidirectional PIM), avoid overlapping multicast group ranges.
- When SSM, IGMPv3 and IGMP snooping are configured, use multicast groups that map to unique Layer 2 multicast MAC addresses. Avoid overlapping Layer 2 multicast MAC addresses.
- Ensure that there is at least one IGMP querier-capable device active in each VLAN. In a VLAN where PIM and IGMP are not configured because the multicast traffic does not need to be routed, enable the IGMP snooping querier.
Replication mode
Egress replication mode provides better performance only when there are a significant number of multicast outgoing interfaces (OIFs) served by DFCs. Without a DFC to support local egress replication mode, egress replication mode performance is lower then ingress replication mode because of the load placed on the PFC.
1. Ingress marking and egress policing are not compatible with egress replication.
2. Egress SPAN is not supported in egress multicast mode.
3. Use the automatically detected replication mode. If possible, the switch will use egress replication mode.
- If you have configured ingress replication mode, enter this command to return to the automatic detection mode:
Router(config)# no mls ip multicast replication-mode ingress
- If you have configured egress replication mode, enter this command to return to the automatic detection mode:
Router(config)# no mls ip multicast replication-mode egress
Local Egress replication mode
If the switch is operating in egress replication mode, enable local egress replication mode.
Router(config)# mls ip multicast egress local
Non-RPF Traffic
The switch uses the NetFlow table to drop non-RPF traffic.
- With a PFC3, configure non-RPF aging:
Router(config)# mls ip multicast non-rpf aging fast
Router(config)# mls ip multicast non-rpf aging global
- With a PFC2, configure rate limiting of RPF failure traffic:
Router(config)# mls rate-limit multicast ipv4 non-rpf pps [packets_in_burst]
Multicast Consistency Checker
Enable the multicast consistency checker:
Router(config)# mls ip multicast consistency-check
Router(config)# mls ip multicast consistency-check type scan-mroute
The RP-SP multicast consistency checker results are most reliable when multicast traffic levels are stable. When multicast traffic levels vary significantly, the RP-SP multicast consistency checker might indicate a problem when none exists.
The RP-SP checker is enabled by default in Release 12.2(33)SXH and later releases.
Traffic Rate Limiting
If you have PIM sparse mode configured, enter this command:
Router(config)# mls rate-limit multicast ipv4 connected packets_per_second
Set a packets-per-second value between 150 and 1000
Directly Connected Subnets
If the switch is not the first hop router for any multicast sources, disable installation of directly connected subnet entries:
Router(config)# no mls ip multicast connected
If the switch is the first hop router for any multicast source, rate-limit the traffic.
Multicast Redundancy and SSO
- Use the default settings.
- With SSO redundancy configured, use static anycast RP.
- With SSO redundancy configured, do not use auto-RP.
- SSO redundancy is supported only for PIM-DM, PIM-SM, SSM protocols.
PIM Snooping
- In VLANs with multicast routers running source-specific multicast (SSM) and directly connected multicast sources, disable PIM snooping in the VLAN:
Router(config)# interface vlan vlan_ID
Router(config-if)# no ip pim snooping
- In VLANs that have multicast routers running PIM sparse mode (PIM-SM) and directly connected multicast sources, enable PIM snooping on the switch and in the VLAN and ensure that DR flooding is enabled on the switch:
Router(config)# ip pim snooping
Router(config)# ip pim snooping dr-flood
Router(config)# interface vlan vlan_ID
Router(config-if)# ip pim snooping
- DR flooding is not required in these cases:
- A VLAN with multicast routers running PIM-SM only and with no directly connected multicast sources.
- A VLAN with multicast routers running SSM only and with no directly connected multicast sources.
- A VLAN with multicast routers running bidirectional PIM only, whether or not there are any directly connected multicast sources.
- If DR flooding is not required on the switch, disable it to reduce bandwidth usage:
Router(config)# no ip pim snooping dr-flood
- CSCsh98208-In a VLAN with PIM snooping configured, when the shared tree and shortest path tree (SPT) diverge, PIM snooping might suppress the (S,G) RPT-bit prune message that is sent by a multicast receiver from reaching the upstream router in the shared tree, causing a situation in which more than one upstream router forwards the multicast traffic, each using their own (S,G)-join state, which in turn causes duplicate multicast packets to be delivered to the multicast receivers.
This situation lasts only briefly because the PIM-ASSERT mechanism stops the extraneous flow, but this cycle repeats again when the next (*,G) join (S,G) RPT bit prune message is sent by one of the receivers.
If the switch is in a topology that has the problem, take one of these actions:
- With Release 12.2(18)SXF9 and later releases, enter this command to disable SGR-prune message suppression:
Router(config)# ip pim snooping suppress sgr-prune
- With releases earlier than Release 12.2(18)SXF9, disable PIM snooping in the VLAN:
Router(config)# interface vlan vlan_ID
Router(config-if)# no ip pim snooping
- PIM dense mode (PIM-DM) is not compatible with PIM snooping.
IGMP Snooping
- With Release 12.2(33)SXH and later releases, to prevent depletion of the switch's hardware table capacity, enter the following command:
Router(config)# ip igmp snooping source-only-learning limit {1000 | 2000}
- Enter 2000 unless Virtual Switching System (VSS) is configured.
- Enter 1000 if VSS is configured.
Modify the value based on the requirements of your network.
- Rate-limit IGMP traffic. Enter the following command:
Router(config)# mls rate-limit multicast ipv4 igmp 5000 100
Modify the packets-per-second and burst values based on the requirements of your network and the available CPU capacity.
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