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Cisco Bug: CSCur32142 - mcast traffic blackhole for upto 4min as assert cancel not sent by winne

Last Modified

Sep 17, 2019

Products (8)

  • Cisco Nexus 7000 Series Switches
  • Cisco Nexus 7000 10-Slot Switch
  • Cisco Nexus 7000 4-Slot Switch
  • Cisco Nexus 7700 6-Slot Switch
  • Cisco Nexus 7700 18-Slot Switch
  • Cisco Nexus 7000 18-Slot Switch
  • Cisco Nexus 7700 10-Slot Switch
  • Cisco Nexus 7000 9-Slot Switch

Known Affected Releases

6.2(10) 6.2(10)S102 7.1(0)D1(0.324)

Description (partial)

Multicast traffic blackhole for up to 4 minutes

If more than one router forwards traffic onto a LAN - in initial bootup phase or  when 'ip multicast multipath' command is configured - PIM assert election happens and one router becomes the winner.  This could be the non-PIM-DR having a PIM receiver. There may also be local IGMP receivers on this LAN.
Now, if the winner receives a PIM Prune message and no other PIM receivers exist on that LAN, the winner should send an assert cancel message, to conclude the election and let the PIM-DR on the LAN forward for local receivers.

Under certain circumstances, the winner does not always send out the assert cancel thereby causing traffic blackhole until the loser router ages out the winner's assert message. This could take up to 4 minutes.
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