Nexus 7K interface error disabled. Reason:DCX-No ACK in 100 PDUs

[c.walsh]

We are deploying a pair of Nexus 7009, running NX-OS version 6.0(4).

Customer is attaching HP servers running ESX via 2 x 10gig connections, 1 connection to each core switch.

Connection to the second switch goes down after a period of time with the error Ethernet4/13 is down (dcxNoACKin100PDUs, port: error)

Has anyone seen this before, FCOE is not enabled on the Switch.

Show interface output.

Ethernet4/13 is down (dcxNoACKin100PDUs, port: error)

  Dedicated Interface

  Hardware: 1000/10000 Ethernet, address: 30f7.0de6.8aa4 (bia 30f7.0de6.8aa4)

  Description: **** MPEP-ESX01 ****

  MTU 1500 bytes, BW 10000000 Kbit, DLY 10 usec

  reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA

  Port mode is trunk

  auto-duplex, 10 Gb/s, media type is 10G

  Beacon is turned off

  Auto-Negotiation is turned on

  Input flow-control is off, output flow-control is off

  Rate mode is dedicated

  Switchport monitor is off

  EtherType is 0x8100

  Last link flapped 00:17:34

  Last clearing of "show interface" counters never

  30 seconds input rate 0 bits/sec, 0 packets/sec

  30 seconds output rate 0 bits/sec, 0 packets/sec

  Load-Interval #2: 5 minute (300 seconds)

    input rate 0 bps, 0 pps; output rate 0 bps, 0 pps

  RX

    5 unicast packets  648 multicast packets  69 broadcast packets

    722 input packets  100656 bytes

    0 jumbo packets  0 storm suppression packets

    0 runts  0 giants  0 CRC  0 no buffer

    0 input error  0 short frame  0 overrun   0 underrun  0 ignored

    0 watchdog  0 bad etype drop  0 bad proto drop  0 if down drop

    0 input with dribble  0 input discard

    0 Rx pause

  TX

    444 unicast packets  514724 multicast packets  11594 broadcast packets

    526762 output packets  38946660 bytes

    3 jumbo packets

    0 output error  0 collision  0 deferred  0 late collision

    0 lost carrier  0 no carrier  0 babble  0 output discard

    0 Tx pause

  5 interface resets

[Prashanth Krishnappa]

What type of 10Gig adapter do you have on the server? I suspect its a FCoE capable CNA and could be sending out DCBX TLVs at times. Do you have LLDP enabled on the Nexus? If LLDP is not needed, you can disable LLDP per interface with following command which should avoid the problem.

20-11-7010-N7k-Core-A(config)# interface ethernet 1/15

20-11-7010-N7k-Core-A(config-if)# no lldp ?

  receive   Enable LLDP reception on interface

  transmit  Enable LLDP transmission on interface

[c.walsh]

We have already applied those commands to one of the Nexus switches & it did resolve the issue.

My concern is that we shouldn't have to configure this as we are not using FCoE.

The servers have emulex adaptors & i am wondering why we were only seeing this issue on one of the Nexus Core switches?

Server team are adamant the problem is not the servers as the have the latest firmware/drivers.

Would like to prove it is not the Nexus!

[Prashanth Krishnappa]

If your servers are not doing FCoE, they should not be sending out DCBX TLVs in LLDP frame. I have had lot of experice with this issue on Nexus 5000 when servers are doing FCoE and this always turned out to be server not sending correct sequence numbers.

Here is a thread on it.

https://supportforums.cisco.com/message/3468650#3468650

[c.walsh]

That is what i suspected, i need to investigate more with the server team!

[ปลาวาฬทราย RMUTT CPE IX]

Did you find the root cause?

Thank you very much.