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Cisco Bug: CSCtc71798 - 3120 L2 dest index incorrectly programmed on cross-stack etherchannel

Last Modified

Jan 24, 2017

Products (95)

  • Cisco Blade Switches for HP
  • Cisco Catalyst 2960-24-S Switch
  • Cisco ME 3400-24TS-A Switch
  • Cisco Catalyst 3560E-24TD-S Switch
  • Cisco Catalyst 3560G-48PS Switch
  • Cisco Catalyst 3560E-12D-E Switch
  • Cisco Catalyst 3750V2-24PS Switch
  • Cisco Catalyst 3750G-12S Switch
  • Cisco Catalyst 3560E-48PD-SF Switch
  • Cisco Catalyst 2960G-24TC-L Switch
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Known Affected Releases


Description (partial)


In a rare situation, the traffic received on a member interface of a cross-stack etherchannel will be dropped by the CBS-3120 stack.

This condition may be observed immediately following a reload of the stack - and be seen on a previously working etherchannel.


In this condition, the switch will drop packets received on certain ports of a cross-stack etherchannel.

To determine if this bug is being hit, each port in the port-channel must be brought up individually.

Here is an example of this condiition:

Po1 is a 4-port etherchannel with ports gig1/0/1, gi2/0/1, gig3/0/1, and 4/0/1.

Traffic is received by Po1, but only forwarded if gi2/0/1 is the port that the traffic is received by.  If gig1/0/1, gig3/0/1, or gig4/0/1 are brought up - the traffic is not forwarded by the switch stack.

The problem is isolated to specific vlans that are forwarding on the etherchannel.  When the condition is seen - some vlans will forward properly and other will not.
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