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What's the meaning of Recv-Q and Send-Q in "netstat -an"?

Question & Answer


Question

Generally, "netstat -an“ shows the state of all socket connections.
# netstat -an
Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
tcp        0      0  *.111                  *.*                    LISTEN
tcp4       0      0  100.300.0.35.10022       100.300.0.173.45521      ESTABLISHED
tcp4       0      0  100.300.0.35.10022       100.300.0.173.21028      ESTABLISHED
tcp        0      0  *.657                  *.*                    LISTEN

 
However, sometimes, we can see some values on Recv-Q and Send-Q. 
What does that mean?

Cause


 

Answer

Recv-Q:
High Recv-Q means the data is put on TCP/IP receive buffer, but the application does not call recv() to copy it from TCP/IP buffer to the application buffer. Customer can check the application listening the port, and see if it is working as expected. For example, if you saw Recv-Q in the following connection:
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)
tcp4    3223      0  11.10.32.24.8002       11.10.32.12.64672      ESTABLISHED

Customer should check the application listening the port 8002.
Send-Q:
High Send-Q means the data is put on TCP/IP send buffer, but it is not sent or it is sent but not ACKed. So, high value in Send-Q can be related to server network congest, server performance issue or data packet flow control, and so on. 
Please note: The send and receive queue sizes are shown in bytes.

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Document Information

Modified date:
31 December 2021

UID

ibm16537582