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Why does ONTAP initiate a connection on a port other than 4045 for for NLM callbacks?

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Category:
ontap-9
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nas
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Applies to

  • ONTAP 9
  • UNIX or UNIX-like operating system
  • NFSv3

Answer

  • Clients request NLM locks with requests sent to ONTAP on port 4045.
  • If a blocking lock cannot be granted immediately, ONTAP will later send a callback to the client when the lock is granted.
  • The callback will be done from ONTAP to the client using a port discovered using the port mapper.
  • Packet trace snippet indicating NLM is being blocked:
1478 2022-08-04 07:07:34.920384 xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx NLM V4 LOCK Call (Reply In 1479) FH:0x91a3284f
1479 2022-08-04 07:07:34.920835 xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx NLM V4 LOCK Reply (Call In 1478) NLM_BLOCKED
  • Packet trace snippet confirming which port is used by the client: 
9 2022-08-04 07:07:10.362505 1xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx Portmap V2 GETPORT Call (Reply In 11) NLM(100021) V:4 TCP
11 2022-08-04 07:07:10.363195 xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx Portmap V2 GETPORT Reply (Call In 9) Port:34726

Additional Information

The NLM port used by ONTAP can be configured using nfs option modify -nlm-port.
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