Cisco 7604-RSP720C-R Configuration Manual page 226

Information About vPCs
S e n d d o c u m e n t c o m m e n t s t o n e x u s 7 k - d o c f e e d b a c k @ c i s c o . c o m
The software keeps the multicast forwarding state synchronized on both of the vPC peer devices. The
IGMP snooping process on a vPC peer device shares the learned Group information with the other vPC
peer device through the vPC peer link; the multicast states are always synchronized on both vPC peer
devices. The PIM process in vPC mode ensures that only one of the vPC peer devices forwards the
multicast traffic to the receivers.
Each vPC peer is a Layer 2 or Layer 3 device. Multicast traffic flows from only one of the vPC peer
devices. You may see duplicate packets in the following scenarios:
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•
You may see negligible traffic loss in the following scenarios:
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Ensure that you dual-attach all Layer 3 devices to both vPC peer devices. If one vPC peer device goes
down, the other vPC peer device continues to forward all multicast traffic normally.
See the Cisco Nexus 7000 Series NX-OS Interfaces Command Reference, Release 5.x, for information on
commands that display information on vPC and multicast.
The following discusses vPC PIM and vPC IGMP/IGMP snooping:
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You should enable or disable IGMP snooping identically on both vPC peer devices, and all the feature
configurations should be identical. IGMP snooping is on by default.
The following commands are not supported in vPC mode:
Note
ip pim spt-threshold infinity
ip pim use-shared-tree-only
See the Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide, Release 5.x, for more
information on multicasting.
Multicast PIM Dual DR (proxy DR )
By default, a multicast router sends PIM joins upstream only if it has interested receivers. These
interested receivers can either be IGMP hosts (they communicate through IGMP reports) or other
multicast routers (they communicate through PIM joins).
In the Cisco NX-OS vPC implementation (in non-F2 mode), PIM works in Dual designated router (DR)
mode. That is, if a vPC device is a DR on a vPC SVI OIF, its peer automatically assumes the proxy DR
role. IGMP adds an OIF (the report is learned on that OIF) to the forwarding if the OIF is a DR. With
Dual DR, both vPC devices have an identical (*,G) entry with respect to the vPC SVI OIFs, as displayed
in the following example:
VPC Device1:
Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x
7-24
Orphan hosts
When the Source and Receivers are in the Layer 2 vPC cloud in different VLANs with multicast
routing enabled and a vPC member link goes down.
When you reload the vPC peer device that is forwarding the traffic.
When you restart PIM on the vPC peer device that is forwarding the traffic.
vPC PIM—The PIM process in vPC mode ensures that only one of the vPC peer devices forwards
multicast traffic. The PIM process in vPC mode synchronizes the source state with both vPC peer
devices and elects with vPC peer device forwards the traffic.
vPC IGMP/IGMP snooping—The IGMP process in vPC mode synchronizes the DR information on
both vPC peer devices. There is a dual-DR concept for IGMP when you are in vPC mode, which is
not available when not in vPC mode, that has both vPC peer devices maintain the multicast group
information between the peers.
Chapter 7 Configuring vPCs
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