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DSCP 26 Not Applied to NFS over RDMA Traffic

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ontap-9
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Applies to

  • ONTAP 9
  • NFS over RDMA (NFSv4.1, proto=rdma) on RoCE-enabled data LIFs
  • Linux NFS clients with NVIDIA/Mellanox NICs

Issue

  • RDMA has been configured according to the "Configure NICs for NFS over RDMA" guide.
  • Outgoing NFS over RDMA packets from ONTAP show DSCP 0 on switches while incoming client packets show DSCP 26.
  • Packet traces show all ONTAP packets with DSCP 0. Client RDMA Connection Manager (CM) ConnectRequest packets advertise Primary Traffic Class: 0x00.

frame 78 (logs/pktt/frame78_req_decode.txt)
802.1Q Virtual LAN, PRI: 0, DEI: 0, ID: 32
Internet Protocol Version 4, Src: 10.x.x.x, Dst: 10.x.x.x
0000 00.. = Differentiated Services Codepoint: Default (0)
Opcode: Unreliable Datagram (UD) - SEND only (100) <- CM message on QP1
Attribute ID: 0x0010 <- ConnectRequest
Destination Port: 0x4e51 <- 20049, NFS over RDMA
Local QPN: 0x001522
Primary Traffic Class: 0x00
0000 .... = Primary SL: 0x0

  • ONTAP NIC counter prio3_tx_frames remains 0 since boot while client and switch DSCP trust, DSCP 26 to priority 3 mapping and PFC settings are correct.

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