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Cisco Bug: CSCum57491 - ethernet CFM Global command causes mac flap

Last Modified

Jan 30, 2017

Products (10)

  • Cisco ME 3400 Series Ethernet Access Switches
  • Cisco ME 3400EG-2CS-A Switch
  • Cisco ME 3400-24TS-A Switch
  • Cisco ME 3400E-24TS-M Switch
  • Cisco ME 3400G-12CS-A Switch
  • Cisco ME 3400G-2CS-A Switch
  • Cisco ME 3400EG-12CS-M Switch
  • Cisco ME 3400-24FS-A Switch
  • Cisco ME 3400G-12CS-D Switch
  • Cisco ME 3400-24TS-D Switch

Known Affected Releases


Description (partial)

Problem:ethernet CFM Global command causes mac flap 

When the "Ethernet CFM global" command is enabled on the switch customer noticed mac flap on Agg switches and remote UPE. The Customer CE uses an encrypting device between both CE and UPE. CE run CFM and this frames are encrypted and ethertype modified. When the CFM configuration is tried in the UPE-1 or UPE-2 (ethernet CFM global) the mac flaps loggs start in the Agg switches and remote UPE. After doing the captures on the customer network below is what we could conclude. When the ME switch has ?Ethernet CFM global? command enabled and if it receives a frame on CFM destination multicast 0180.c200.003x, and ethertype other than the CFM ether-type(0x8902) the switch is looping back the frame received on one interface to the same interface with modifying the COS value to 7.  We could reproduce the issue in the CALO lab as well. This is causing customer bfd flaps and intern protocol flaps.

When the Switch receive the Ethernet CFM  packet with DST mac address as CFM adress and E-type as Unknown Ether type, during this time we are punting/rewrite and sending with higher cos on the  same interface. causing the mac flap.
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