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Cisco Bug: CSCum23621 - Multicast assert processing on Nexus 7k

Last Modified

Jul 05, 2018

Products (7)

  • Cisco Nexus 7000 Series Switches
  • Cisco Nexus 7000 10-Slot Switch
  • Cisco Nexus 7000 4-Slot Switch
  • Cisco Nexus 7000 18-Slot Switch
  • Cisco Nexus 7700 18-Slot Switch
  • Cisco Nexus 7700 10-Slot Switch
  • Cisco Nexus 7000 9-Slot Switch

Known Affected Releases

6.2(2a)

Description (partial)

Symptom:
Period duplicates (every 180 seconds) for a short time < 1sec. 

n a nutshell ,    we have a setup using mvpn  with a mix of N7K (6.2.2a ) and Cat6k Sup2T (150-1.SY4)
 
All the boxes shares a default  mdt for each vrf  ( 2 in our set-up)
 
We are using  2  Cat6K as  ASBR   in an inter-AS VPN scenario ( inter option A) and  N7Ks  are acting as PE
 
In  high level this is our set-up :
 
                                                                          Source
                                                                               |
                                                                          Cat6k3
                                                                      /                 \
Cat6k1                 Cat6k2
                                                               |                           |
           Receiver-N7K1-----------  Pnode ----------- P node --------------- N7K2-Receiver
 
 
n  In a stable situation :  
o   N7K1 use Cat6k2 for it's RPF to the source   N7K2 use cat6k1 for its rpf to the source
o   Cat6k2 ( router name RP74)  forwards the traffic to the default mdt
n  Cat6K3 to Cat6K2 link is shut down    à Cat6K1 (router name RP75) forward the traffic to the mdt
n  The link recover   à   Cat6k2 receives PIM join message from the N7K  and starts forwarding traffic to the default MDT
n  This result in an PIM assert  that Cat6K1 win   ( same metric, highest IP )
n  N7K2 does not adapt its  RPF based on the PIM assert result and keep sending PIM join to Cat6K2.
n  Cat6k2 start forwarding to the mdt   resulting in PIM assert ........

Conditions:
An assert scenario i.e. having two upstream and two downstream routers, where one downstream router sends a PIM join to one upstream router and the other downstream router sends a join to the other upstream router.
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