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Cisco Bug: CSCvr95643 - Silent loss and TCP Re-transmissions seen with certain host pcs connected to c9300-48UXM

Last Modified

Aug 25, 2020

Products (32)

  • Cisco Catalyst 9300 Series Switches
  • Cisco Catalyst 9300-48P-A Switch
  • Cisco Catalyst 9300-48U-A Switch
  • Cisco Catalyst 9300-48UN-A Switch
  • Cisco Catalyst C9500-16X-E Switch
  • Cisco Catalyst 9400 Supervisor Engine-1XL-Y
  • Cisco Catalyst 9300-48UXM-A Switch
  • Cisco Catalyst 9300-48T-A Switch
  • Cisco Catalyst C9500-12Q-A Switch
  • Cisco Catalyst 9300-24T-A Switch
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Known Affected Releases


Description (partial)

Hosts directly connected to an mgig Cat9300 switch may experience lower than expected throughput while trying to download files from remote servers. Simultaneous captures on the switch uplink and host port may show a small amount of silent loss (average 100 out of 1 million packets lost). 

This is most likely to be seen with downloads from the internet where there is a larger round-trip latency. Local LAN transfers with single digit round-trip times are unlikely to see any performance impact from this amount of loss.

Certain NIC cards when connected to 9300 mGig port causes interop issues resulting in silent drops of the packets at the end client.

Loss is completely silent from the switch perspective so it can be difficult to isolate. Rule out any cabling problems or genuine issues with the host or switch port. This is specific to mGig interfaces on the Cat9300.
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