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NFS hangs due to half-open TCP session

  1. Last updated
    Jan 22, 2025
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19,035
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Votes:
19
Category:
ontap-9
Specialty:
nas
Last Updated:
1/22/2025, 10:06:34 PM

 

Applies to

  • ONTAP
  • NFS
  • Stateful firewall

Issue

  • NFS Operations Hang:

    • NFS operations hang, requiring a reboot to restore access to the NFS mount.
      • e.g. df, ls, and umount
    • Client error:
      • e.g. <linux-client> kernel: nfs: <server> not responding, still trying
  • Packet Traces indicate a repeating loop
    1. The client sends a TCP SYN reusing the same ephemeral port.
    2. ONTAP responds with a challenge ACK, expecting a TCP RST from the client.
    3. The challenge ACK or RST is blocked by the firewall, causing the client to retransmit the SYN.
  • Behavior is often seen after a Firewall upgrade/reboot.

​

 

 

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