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Cisco Bug: CSCta55476 - N7K: Learning breaks on non-vpc uplinks after vPC peer failure

Last Modified

Jan 28, 2017

Products (1)

  • Cisco Nexus 7000 Series Switches

Known Affected Releases

4.1(5) 4.2(1)

Description (partial)

Symptom:

1. MAC address learning breaks on non-VPC L2 ports when the vPC peer is reloaded or the peerlink is brought down. This happens when the last member of a port-channel on a line card goes down. The packets are flooded; hence there is no packet loss.

2.  After (1) happens, if there is a port-flap of non-vPC L2 ports, L2 learning on non-vPC L2 ports is restored, but MAC address learning happens on vPC peer-link, and this can result in packet drops.

This problem does not exist in 4.2(1), but existed in the releases prior to 4.2(1) release of Nx-OS. 
But, an upgrade of Nx-OS from an older version like 4.1(5) to 4.2(1) would not automatically fix the issue. An upgrade from any older image to 4.2(2) automatically fixes up the problem.
Conditions:

When the last member of the peer-link port-channel on a given line card goes down, this results in learning being disabled on all non-vPC L2 ports on the line card. After this, if a flap occurs, learning on non-vPC L2 ports is restored, but learning is enabled on vPC peer-links.
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