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High number of RECEIVE discards due to No buffer on CX5 NIC due to MTU mismatch

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Category:
ontap-9
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nas
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Applies to

  • ONTAP 9
  • CX5 NIC

Issue

  • IFSTAT reports high number of discards on RECEIVE, even though system does not have high CPU utilization
    • Total discards counter value equals No buffer counter value, indicating that all the discards are caused by no buffer events
    •   RECEIVE
       Total frames:     3694m | Frames/second:   52114  | Total bytes:     17709g
       Bytes/second:      249m | Total errors:        0  | Errors/minute:       0
       Total discards:    415k | Discards/minute:   351  | Multi/broadcast:  2232k
       Non-primary u/c:     0  | Errored frames:      0  | Unsupported Op:      0
       CRC errors:          0  | Runt frames:         0  | Fragment:            0
       Long frames:         0  | Jabber:              0  | Length errors:       0
       Alignment errors:    0  | No buffer:         415k | Pause:               0
       Jumbo:            2184m | Error symbol:        0  | Bus overruns:        0
       Queue drops:         0  | LRO segments:     1641m | LRO bytes:       17545g
       LRO6 segments:       0  | LRO6 bytes:          0  | Bad UDP cksum:       0
       Bad UDP6 cksum:      0  | Bad TCP cksum:       0  | Bad TCP6 cksum:      0
       Mcast v6 solicit:    0  | Lagg errors:         0  | Lacp errors:         0
       Lacp PDU errors:     0
  • NETWORK-PORTS ASUP shows that ONTAP MTU is 9000
  • BSD-NETSTAT-ANCEWCT ASUP shows that the biggest MSS to data LIF IPs is 1460, indicating that the network MTU is 1500

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