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Cisco Bug: CSCuo82093 - Duplicate multicast packets are detected in a mVPN N7k design

Last Modified

Nov 27, 2020

Products (1)

  • CiscoPro Workgroup EtherSwitch Software

Known Affected Releases

6.1(2)E10 6.2(10)S83

Description (partial)

Symptom:
- The Customer Edge (CE) Multicast Receiver would receive duplicate multicast packets for a time of 1 - 10 seconds
- These receivers are physically located behind one or more Provider Edge routers running IOS based code 
- The CE Multicast Sources are physically located behind a pair of Nexus 7000 in a VPC domain

Conditions:
- These symptoms occurs in a mVPN design where the N7k are positioned as Provider Edge and the Multicast Sources are part of a VPC domain. The pair of N7ks are also configured for Rendezvous Points for the Customer Edge vrf. 
- Order of operations:

1. Remote CE joins a multicast group, Last-Hop-Router (FHR) at the Customer Edge sent a *,G to the RP.
2. A *,G tree is created in the MPLS core from the IOS PE to the remote NX-OS PE-1 (PE-1 = primary RP)
3. When the Last-Hop-Router (LHR) receives the first multicast packet via the *,G tree it will try to join the S,G tree
4. The local PE for LHR will send a S,G towards the Source PE, but the preferred path is now via NX-OS PE-2 (PE-2 - secondary RP)
5. The NX-OS PE-2 will now add the MDT tunnel to the OIL and the multicast traffic will via the S,G tree
6. The Receiver now receives duplicate multicast packets, one via *,G and one via S,G
7. The duration of duplicate packets can range from 1 - 60 seconds
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