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Cisco Nexus 5000 Series NX-OS Interfaces Operations Guide, Release 5.0(3)N2(1)
Chapter 2 Cisco Nexus 5500 Platform Layer 3 and vPC Operations
Using a vPC Switch as a Designated Router (PIM DR)
Note As of Cisco NX-OS Release 5.0(3)N1(1b), the no ip igmp snooping mrouter vpc-peer link command
cannot be applied with FEX dual-homed topologies due to a software limitation. The command is used
only for interfaces on a Cisco Nexus 5500 Platform switch. This software limitation will be removed in
a future software release.
One post-routed multicast packet is sent to a vPC peer link using a reserved VLAN. To configure the
reserved VLAN, use the follow commands:
switch-Layer 3-1(config)# vpc bind-vrf vrf name vlan VLAN ID
switch-Layer 3-1(config)# vpc bind-vrf default vlan 3000
One reserved VLAN is required for each VRF. Without these commands, the receivers in non-vPC
VLAN and the receivers connected to Layer 3 interfaces may not receive multicast traffic. The non-vPC
VLANs are the VLANs that are not trunked over a peer link.
Multicast traffic that is received over a peer link (with a VLAN ID other than the reserved VLAN ID) is
not routed. The multicast traffic is treated as Layer 2 frames that are sent to orphan ports only and not
to vPC member ports. The multicast traffic that is received over a peer link with a reserved VLAN ID is
routed to a non-vPC VLAN (shown as VLAN 13 in Figure 2-10) and receivers behind the Layer 3
interface. The receivers behind the Layer 3 interface can be hosts directly connected to the Cisco Nexus
5500 Platform switch using Layer 3 interfaces or a router joins the source tree.
Figure 2-10 shows the multicast forwarding rules in a vPC dual-DR topology. In this topology, the
source in VLAN 10 and receivers in VLAN 11 and VLAN 12 are the vPC hosts (although in this example
they are hosts behind a dual-homed FEX topology where the same rule applies to hosts directly to a
Cisco Nexus 5500 Platform switch in a vPC topology). VLAN 13 is a non-vPC VLAN and resides only
on N5k-2.
Figure 2-10 Multicast Data Forwarding
Source
VLAN 10
Receiver
VLAN 11
Receiver
VLAN 12
Receiver
L3 interface
Receiver
VLAN 13
N5k-1
N5k-2
L2
L3
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Reserved VLAN
Pseudo DR PIM DR
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