[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [lwip-users] ACK missing after SYN, strange high Ack Num
From: |
Jochen Strohbeck |
Subject: |
Re: [lwip-users] ACK missing after SYN, strange high Ack Num |
Date: |
Wed, 1 Jun 2022 12:56:56 +0200 |
Hello Indan!
As far as I understand the trace, the ACK is to the SYN packet before
(49564):
328782 137.544808074 192.168.0.6 192.168.0.100 TCP 74 [TCP
Port numbers
reused] 49564 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1
TSval=1370931857 TSecr=0 WS=128
328783 137.545136624 192.168.0.100 192.168.0.6 TCP 60 80 →
49564 [ACK]
Seq=1 Ack=4286058530 Win=2764 Len=0
328784 137.545170810 192.168.0.6 192.168.0.100 TCP 54 49564 →
80 [RST]
Seq=4286058530 Win=0 Len=0
328785 137.553397500 192.168.0.6 192.168.0.100 TCP 74 [TCP
Retransmission] [TCP Port numbers reused] 49564 → 80 [SYN] Seq=0
Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=1370931865 TSecr=0 WS=128
328786 137.553698566 192.168.0.100 192.168.0.6 TCP 60 [TCP
Dup ACK
328783#1] 80 → 49564 [ACK] Seq=1 Ack=4286058530 Win=2764 Len=0
328787 137.553751807 192.168.0.6 192.168.0.100 TCP 54 49564 →
80 [RST]
Seq=4286058530 Win=0 Len=0
The sender sends an RST to 49564. It make one more retry with the same
result and the request fails with timeout error. Is my interpretation
correct?
BTW: I noticed that this failed TCP connection 49564 is not logged if
TCP_DEBUG is enabled which means that a lower lwip layer handled this
connection request.
Do you know where which function / code makes the decision to do a ACK
after SYN? Probably I can trace back from here to find the root cause.
So telling from you post: ACKing on SYN is the correct behavior for a
device which is not able to process the connection request?
I still wonder about the 'insane high' number 4286058530 in the '[ACK]
Seq=1 Ack=4286058530' reply, so I'm not sure if the protocol handling is
correct here.
Regards,
Jochen
- Re: [lwip-users] ACK missing after SYN, strange high Ack Num, Jochen Strohbeck, 2022/06/01
- Re: [lwip-users] ACK missing after SYN, strange high Ack Num, Indan Zupancic, 2022/06/01
- Re: [lwip-users] ACK missing after SYN, strange high Ack Num,
Jochen Strohbeck <=
- Re: [lwip-users] ACK missing after SYN, strange high Ack Num, Indan Zupancic, 2022/06/01
- Re: [lwip-users] ACK missing after SYN, strange high Ack Num, Jochen Strohbeck, 2022/06/02
- Re: [lwip-users] ACK missing after SYN, strange high Ack Num, Indan Zupancic, 2022/06/02
- Re: [lwip-users] ACK missing after SYN, strange high Ack Num, Jochen Strohbeck, 2022/06/07
- Re: [lwip-users] ACK missing after SYN, strange high Ack Num, Indan Zupancic, 2022/06/07