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Cisco Bug: CSCuo78312 - Packet drop due to TX MTU verification for specific frame sizes

Last Modified

Mar 05, 2018

Products (1)

  • Cisco Catalyst 6000 Series Switches

Known Affected Releases


Description (partial)

Packet drop seen for locally sourced traffic when generating packets below configured system jumbomtu.
Drops are caused by Dhanush port ASIC at WS-X6148A-GE-45AF line card.

Additional tests showed the following behavior:
a) for configured jumbomtu less or equal to 1603 bytes: ICMP traffic is dropped above Jumbomtu-8 bytes.
b) for configured jumbomtu higher or equal to 1604 bytes and less or equal to 1606 bytes: ICMP traffic is dropped between 1597 and 1600 bytes.
c) for configured jumbomtu equal to 1607 bytes: ICMP traffic is dropped for size equal to 1600 bytes.
d) for configured jumbomtu higher than 1607 bytes: packet drops are no longer seen irrespective of MTU size

Drop behavior seen for locally sourced traffic only (example: routing protocols related packets, icmp request packets). 
Only locally sourced TX traffic is affected by this behavior. RX traffic or L2 switched traffic are not affected.
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