Cisco Support Community
Community Member

Multicast: duplicated packets on nexus 7k with vpc and HSRP

Hi guys,

I'm testing multicast deployment on the lab shown below. The sender and the receiver are connected to the 6500 in two different vlans. The sender is in vlan 23 and the reciever in vlan 500. They are connected to the 6500 with a trunk link. There is VPc between the two nexus 7k and the 6500.

Furthermore, there is HSRP running on the two vlan interface 23 and 500 on both nexus.

I have configured the minimum to use PIM-SM with static RP. The RP is the 3750 above the nexus. (*,G) and (S,G) states are created correctly.

IGMP snopping is enabled on 6500, and the two nexus.

I'm using iperf to generate my flow, and netflow and snmp to monitor what happens.

All works correctly, my receiver receive the flow and it takes the good route. My problem is that I have four times more multicast traffic on the vlan interface 500 on both nexus but this traffic is only sent one time to the receiver (which is the good comportment) and the rest of the traffic is not shown on any other physical interface in outbound.

Indeed, I'm sending one flow, the two nexus receive it (one from peer link and the other from the 6500) in the vlan 23 (for example 25 packets inbound).

But when the flow is routed in the vlan 500, there is 100 packets on each interface vlan 500 on each nexus in outbound.

And when monitoring all physical interfaces, I only see 25 packets outbound on the interface linked with the receiver and the overflow isn't outgone.

I have joined the graphs I obtain on one of the nexus for the vlan 23 and the vlan 500. Netflow says the same things in bits/s.

Had someone already seen that? Any idea about the duplication of the packets?

Thanks for any comment,



Nexus 1: n7000-s1-dk9.5.2.7.bin, 2 SUP1, 1 N7K-M132XP-12, 1 N7K-M148GS-11

Nexus 2: n7000-s1-dk9.5.2.7.bin, 2 SUP1, 1 N7K-M132XP-12, 1 N7K-M148GS-11

6500: s72033-adventerprisek9_wan-mz.122-33.SXI5.bin (12.2(33)SXI5)

3750: c3750-ipservicesk9-mz.122-50.SE5.bin (12.2(50)SE5)

Everyone's tags (5)
Community Member

Some guess:

Some guess:

1. At the final state, both Nexus will build (S,G) which with VLAN 23 as incoming interface and VLAN 500 as outgoing interface.

2. Let's assume Nexus1 receives the 1st multicast traffic, it will forward it to vlan 500 (*)

3. Nexus 1 will send the multicast over the peer link on VPC vlan 500 to reach VLAN 500 orphan ports on Nexus2 (*), unless you issue "no ig igmp snooping mrouter vpc-peer-link.

4. Nexus 1 sends another copy over Peer-link for none VPN vlans and routed ports on Nexus 2 (*). This may not count to VLAN 500 traffic, but I am not sure.



CreatePlease to create content