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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)


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.

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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