[lwip-devel] [bug #65742] If no response is received to close the TCP connection, tcp_pcb is released after 40 minutes

[Jiri Engelthaler]

URL:
  <https://savannah.nongnu.org/bugs/?65742>

                 Summary: If no response is received to close the TCP
connection, tcp_pcb is released after 40 minutes
                   Group: lwIP - A Lightweight TCP/IP stack
               Submitter: engy
               Submitted: Tue 14 May 2024 12:12:53 PM UTC
                Category: TCP
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: 2.2.0


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Follow-up Comments:


-------------------------------------------------------
Date: Tue 14 May 2024 12:12:53 PM UTC By: Jiri Engelthaler <engy>
If no response is received to close the TCP connection, tcp_pcb is set to the
FIN_WAIT_1 state, FIN is sent, and if no response is received, tcp_pcb is
released after TCP_MAXRTX (12) retries. That is, after 40 minutes.

Tue May 14 04:57:32 2024 : tcp_connect to port 502
Tue May 14 04:57:32 2024 : tcp_output_segment: rtseq 6509
Tue May 14 04:57:35 2024 : tcp_receive: pcb->rttest 0 rtseq 6509 ackno 6510
Tue May 14 04:57:35 2024 : tcp_recved: received 6 bytes, wnd 20480 (0).
Tue May 14 04:57:35 2024 : tcp_fasttmr: delayed ACK
*Tue May 14 04:57:55 2024 : tcp_close: closing in Tue May 14 04:57:55 2024 :
State: ESTABLISHED*
Tue May 14 04:57:55 2024 : tcp_output_segment: rtseq 6510
Tue May 14 04:57:57 2024 : tcp_slowtmr: rtime 6 pcb->rto 6
Tue May 14 04:57:57 2024 : tcp_output_segment: rtseq 6510
Tue May 14 04:58:03 2024 : tcp_slowtmr: rtime 12 pcb->rto 12
Tue May 14 04:58:03 2024 : tcp_output_segment: rtseq 6510
Tue May 14 04:58:16 2024 : tcp_slowtmr: rtime 24 pcb->rto 24
Tue May 14 04:58:16 2024 : tcp_output_segment: rtseq 6510
Tue May 14 04:58:40 2024 : tcp_slowtmr: rtime 48 pcb->rto 48
Tue May 14 04:58:40 2024 : tcp_output_segment: rtseq 6510
Tue May 14 04:59:29 2024 : tcp_slowtmr: rtime 96 pcb->rto 96
Tue May 14 04:59:29 2024 : tcp_output_segment: rtseq 6510
Tue May 14 05:01:08 2024 : tcp_slowtmr: rtime 192 pcb->rto 192
Tue May 14 05:01:08 2024 : tcp_output_segment: rtseq 6510
Tue May 14 05:04:26 2024 : tcp_slowtmr: rtime 384 pcb->rto 384
Tue May 14 05:04:26 2024 : tcp_output_segment: rtseq 6510
Tue May 14 05:11:02 2024 : tcp_slowtmr: rtime 768 pcb->rto 768
Tue May 14 05:11:02 2024 : tcp_output_segment: rtseq 6510
Tue May 14 05:17:38 2024 : tcp_slowtmr: rtime 768 pcb->rto 768
Tue May 14 05:17:38 2024 : tcp_output_segment: rtseq 6510
Tue May 14 05:24:14 2024 : tcp_slowtmr: rtime 768 pcb->rto 768
Tue May 14 05:24:14 2024 : tcp_output_segment: rtseq 6510
Tue May 14 05:30:51 2024 : tcp_slowtmr: rtime 768 pcb->rto 768
Tue May 14 05:30:51 2024 : tcp_output_segment: rtseq 6510
Tue May 14 05:37:26 2024 : tcp_slowtmr: rtime 768 pcb->rto 768
Tue May 14 05:37:26 2024 : tcp_output_segment: rtseq 6510
Tue May 14 05:37:26 2024 : tcp_slowtmr: max DATA retries reached
*Tue May 14 05:37:26 2024 : tcp_pcb_purge*
Tue May 14 05:37:26 2024 : tcp_pcb_purge: data left on ->unacked


The same problem occurs when sending data if the counterparty does not
respond.

So is the default value of 12 for TCP_MAXRTX OK when it takes 40 minutes?







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File Attachments:


-------------------------------------------------------
Name: tcp_close.pcap  Size: 1KiB
<https://file.savannah.nongnu.org/file/tcp_close.pcap?file_id=56049>

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