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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

15.1(2)SY

Description (partial)

Symptom:
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

Conditions:
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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