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  • Trouble finding info on the TCP Accept sequence changing the port targe

    From R.Wieser@21:1/5 to All on Mon May 3 20:33:57 2021
    Hello all,

    I'm currently trying to figure out how, at the level of ethernet packets,
    the TCP Connect works. I can find quite a number of webpages what the the initial three handshake packets look like, but no more.

    More specific : how an Accept call on the listening socket tells the other
    side that the target port has changed (to a newly created socket, so the listening socket is free to accept another connection).

    If someone knows where I can find that specific info (including SYN, ACK,
    RST, ETC - preferrably with some schematic / pictures) I would be obliged.

    Regards,
    Rudy Wieser

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  • From JJ@21:1/5 to R.Wieser on Tue May 4 18:20:43 2021
    On Mon, 3 May 2021 20:33:57 +0200, R.Wieser wrote:
    Hello all,

    I'm currently trying to figure out how, at the level of ethernet packets,
    the TCP Connect works. I can find quite a number of webpages what the the initial three handshake packets look like, but no more.

    More specific : how an Accept call on the listening socket tells the other side that the target port has changed (to a newly created socket, so the listening socket is free to accept another connection).

    If someone knows where I can find that specific info (including SYN, ACK, RST, ETC - preferrably with some schematic / pictures) I would be obliged.

    That's what Image search engines were designed for. Just use relevant
    keywords like these:

    tcp syn ack fin

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From R.Wieser@21:1/5 to All on Tue May 4 14:15:59 2021
    JJ,

    That's what Image search engines were designed for. Just use
    relevant keywords like these:

    tcp syn ack fin

    Finding the right keywords must than be my problem, as I've been searching
    for the relevant info for quite a bit before posting about it here.

    But are you sure ? When I throw those into them all I get is (stuff like) this :

    https://www.guru99.com/tcp-3-way-handshake.html https://www.cspsprotocol.com/tcp-connection-termination/ https://packetlife.net/blog/2010/jun/7/understanding-tcp-sequence-acknowledgment-numbers/
    https://ipwithease.com/what-is-tcp-fin-packet/ https://www.xmodulo.com/capture-tcp-syn-ack-fin-packets-tcpdump.html
    etc.

    I've found most of those websites using other keywords. "tcp syn ack" wil just give you links to the initial connection, and "fin" will give you info about closing it - as shown with the above results. No info about how accepting (on a listening socket) works or which TCP packets are involved though. :-|

    Regards,
    Rudy Wieser

    --- SoupGate-Win32 v1.05
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  • From JJ@21:1/5 to R.Wieser on Wed May 5 16:41:59 2021
    On Tue, 4 May 2021 14:15:59 +0200, R.Wieser wrote:

    Finding the right keywords must than be my problem, as I've been searching for the relevant info for quite a bit before posting about it here.

    But are you sure ? When I throw those into them all I get is (stuff like) this :

    https://www.guru99.com/tcp-3-way-handshake.html https://www.cspsprotocol.com/tcp-connection-termination/ https://packetlife.net/blog/2010/jun/7/understanding-tcp-sequence-acknowledgment-numbers/
    https://ipwithease.com/what-is-tcp-fin-packet/ https://www.xmodulo.com/capture-tcp-syn-ack-fin-packets-tcpdump.html
    etc.

    I've found most of those websites using other keywords. "tcp syn ack" wil just give you links to the initial connection, and "fin" will give you info about closing it - as shown with the above results. No info about how accepting (on a listening socket) works or which TCP packets are involved though. :-|

    For articles/images which dwells on TCP in details, perhaps adding `rfc`
    search keyword may help refining the search. Throw in non ambiguous
    technical terms which are relevant to what you're trying to find.

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  • From R.Wieser@21:1/5 to All on Wed May 5 12:27:51 2021
    JJ,

    For articles/images which dwells on TCP in details, perhaps adding
    `rfc` search keyword may help refining the search.

    :-) Although I'm sometimes able to extract what I need from those RFCs I
    most always find them quite unreadable. :-( They might be good as
    reference material (aka: looking back), but when trying to figure out what
    to do (aka: looking forward) they are not all that great ... At least, not
    to me.

    Throw in non ambiguous technical terms which are relevant to
    what you're trying to find.

    A good suggestion. Than again, what do you think I've been trying to do ? "connect", "listen" and "accept" won't work as they are way to ambiguous, regardless of being combined with words like "win32", "TCP", "packets", "ethernet", "wireshark" or "handshake".

    Regards,
    Rudy Wieser

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From tecoop@gmail.com@21:1/5 to R.Wieser on Wed May 5 07:28:06 2021
    On Wednesday, May 5, 2021 at 4:28:04 AM UTC-6, R.Wieser wrote:
    JJ,
    For articles/images which dwells on TCP in details, perhaps adding
    `rfc` search keyword may help refining the search.
    :-) Although I'm sometimes able to extract what I need from those RFCs I
    most always find them quite unreadable. :-( They might be good as
    reference material (aka: looking back), but when trying to figure out what
    to do (aka: looking forward) they are not all that great ... At least, not
    to me.
    Throw in non ambiguous technical terms which are relevant to
    what you're trying to find.
    A good suggestion. Than again, what do you think I've been trying to do ? "connect", "listen" and "accept" won't work as they are way to ambiguous, regardless of being combined with words like "win32", "TCP", "packets", "ethernet", "wireshark" or "handshake".

    Regards,
    Rudy Wieser

    I just tried, "tcp internals - port accept" in Google and it turned up some promising links...

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From R.Wieser@21:1/5 to All on Wed May 5 19:07:38 2021
    tecoop,

    I just tried, "tcp internals - port accept" in Google and it turned up
    some promising links...

    I followed a lot of those links (spending at least an hour if not multiple)
    but could not find the info I'm looking for. Why do you think I posted my question here ?

    Also, my second post in this thread shows I found a number of those
    "promising links" and an explanation to why they did not pay off.

    If you found the link to the info I would much obliged if you would post it.

    ... Or should I make it a challenge, just so you follow those links yourself and realise that none of them lead anywhere. :-)

    Regards,
    Rudy Wieser

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