.. titel: TCP State Machine Interactive Diagram
.. slug: tcp-state-maskine
.. dato: 27-03-2026 12:00:00 UTC
.. tags: netværk, tcp, rfc793, tilstandsmaskine, lommeregner, værktøj
.. kategori: Lommeregnere
.. link:
.. beskrivelse: Klikbar TCP-tilstandsmaskinediagram, der dækker alle RFC 793-tilstande. Viser udløsende hændelser, udvekslede pakker, timere og diagnosetip til almindelige fastlåste tilstande.
.. type: tekst
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<div class="calc-container">
<div class="calc-header">
<h2>TCP State Machine Interactive Diagram</h2>
<p>Klik på en hvilken som helst tilstandsknude for at se udløsende hændelser, udvekslede pakker, timere og tip til diagnose i fast tilstand.</p>
<div class="legend">
<div class="legend-item"><div class="legend-dot" style="background:#28a745"></div>Start-/sluttilstande</div>
<div class="legend-item"><div class="legend-dot" style="background:#4CAF50"></div>Normale tilstande</div>
<div class="legend-item"><div class="legend-dot" style="background:#dc3545"></div>TIME_WAIT / sidder fast</div>
<div class="legend-item"><div class="legend-dot" style="background:#f7971e"></div>Lukkestater</div>
</div>
</div>
<div class="result-section">
<div class="section-header">Statsdiagram</div>
<div class="section-content" style="padding:12px">
<div id="cy"></div>
</div>
</div>
<div class="result-section" id="detailPanel">
<div class="section-header">Statsdetaljer</div>
<div class="section-content" id="detailContent">
<p style="color:#999">Klik på en tilstandsknude ovenfor for at se detaljer.</p>
</div>
</div>
</div>
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const STATE_DATA = {
    CLOSED:     { color:'#28a745', event:'Initial state. No connection.',
        packet:'—', timer:'—',
        desc:'No connection exists. Starting point for both client (active open) and server (passive open).',
        diagnosis:'' },
    LISTEN:     { color:'#0f3460', event:'Server calls listen(). Waiting for SYN.',
        packet:'Receives SYN', timer:'—',
        desc:'Server is waiting for an incoming connection request.',
        diagnosis:'Stuck LISTEN: Port not open. Check: ss -lntp | grep &lt;port&gt;' },
    SYN_SENT:   { color:'#0f3460', event:'Client calls connect(). SYN sent.',
        packet:'Sends SYN', timer:'SYN-timeout (~75s)',
        desc:'Client sent SYN, waiting for SYN-ACK.',
        diagnosis:'Stuck SYN_SENT: Firewall dropping SYN, or server not listening. Check MTU/PMTUD if SYN goes out but SYN-ACK never arrives.' },
    SYN_RCVD:   { color:'#0f3460', event:'SYN received. SYN-ACK sent.',
        packet:'Receives SYN, sends SYN-ACK', timer:'SYN-backlog timer',
        desc:'Server received SYN, replied with SYN-ACK, waiting for ACK (3-way handshake).',
        diagnosis:'Many SYN_RCVD: SYN flood / DDoS. Enable tcp_syncookies: sysctl -w net.ipv4.tcp_syncookies=1' },
    ESTABLISHED:{ color:'#28a745', event:'ACK received. Connection open.',
        packet:'ACK completes handshake', timer:'Keepalive (optional, ~7200s default)',
        desc:'The normal data transfer state. Both endpoints can send and receive data.',
        diagnosis:'' },
    FIN_WAIT_1: { color:'#f7971e', event:'Application calls close(). FIN sent.',
        packet:'Sends FIN', timer:'—',
        desc:'Active closer sent FIN, waiting for ACK or FIN from peer.',
        diagnosis:'' },
    FIN_WAIT_2: { color:'#f7971e', event:'FIN-ACK received. Waiting for peer FIN.',
        packet:'Received ACK for FIN', timer:'tcp_fin_timeout (60s default)',
        desc:'ACK received for FIN, waiting for remote FIN to complete half-close.',
        diagnosis:'Stuck FIN_WAIT_2: Remote app never called close(). Reduce tcp_fin_timeout. ss -ant state fin-wait-2' },
    CLOSE_WAIT: { color:'#dc3545', event:'FIN received from peer. ACK sent.',
        packet:'Receives FIN, sends ACK', timer:'—',
        desc:'Passive closer received FIN. Waiting for local application to close().',
        diagnosis:'Many CLOSE_WAIT: Application bug — app not calling close() after receiving EOF. Profile the application for socket leaks.' },
    CLOSING:    { color:'#f7971e', event:'Both sides send FIN simultaneously.',
        packet:'FIN sent and FIN received', timer:'—',
        desc:'Simultaneous close — both sides sent FIN at same time. Rare.',
        diagnosis:'' },
    LAST_ACK:   { color:'#f7971e', event:'Passive closer sends FIN. Waiting final ACK.',
        packet:'Sends FIN', timer:'—',
        desc:'Passive closer sent its FIN, waiting for final ACK from active closer.',
        diagnosis:'' },
    TIME_WAIT:  { color:'#dc3545', event:'Final FIN received and ACKed.',
        packet:'Sends final ACK', timer:'2×MSL (60–120s, linux default 60s)',
        desc:'Waiting 2×MSL to ensure remote received the final ACK, and to prevent old segments from being accepted by a new connection.',
        diagnosis:'Many TIME_WAIT: Normal under high connection rate. Mitigate: tcp_tw_reuse=1, reduce tcp_fin_timeout, use persistent connections, or load balance across more ports.' },
};

const EDGES = [
    {from:'CLOSED',to:'LISTEN',label:'passive open\nlisten()'},
    {from:'CLOSED',to:'SYN_SENT',label:'active open\nconnect()'},
    {from:'LISTEN',to:'SYN_RCVD',label:'rcv SYN\nsnd SYN-ACK'},
    {from:'SYN_SENT',to:'ESTABLISHED',label:'rcv SYN-ACK\nsnd ACK'},
    {from:'SYN_SENT',to:'SYN_RCVD',label:'rcv SYN\n(simultaneous)'},
    {from:'SYN_RCVD',to:'ESTABLISHED',label:'rcv ACK'},
    {from:'SYN_RCVD',to:'FIN_WAIT_1',label:'close()\nsnd FIN'},
    {from:'ESTABLISHED',to:'FIN_WAIT_1',label:'close()\nsnd FIN'},
    {from:'ESTABLISHED',to:'CLOSE_WAIT',label:'rcv FIN\nsnd ACK'},
    {from:'FIN_WAIT_1',to:'FIN_WAIT_2',label:'rcv ACK'},
    {from:'FIN_WAIT_1',to:'CLOSING',label:'rcv FIN\nsnd ACK'},
    {from:'FIN_WAIT_1',to:'TIME_WAIT',label:'rcv FIN+ACK\nsnd ACK'},
    {from:'FIN_WAIT_2',to:'TIME_WAIT',label:'rcv FIN\nsnd ACK'},
    {from:'CLOSE_WAIT',to:'LAST_ACK',label:'close()\nsnd FIN'},
    {from:'CLOSING',to:'TIME_WAIT',label:'rcv ACK'},
    {from:'LAST_ACK',to:'CLOSED',label:'rcv ACK'},
    {from:'TIME_WAIT',to:'CLOSED',label:'2×MSL\ntimeout'},
];

const positions = {
    CLOSED: {x:400,y:50}, LISTEN: {x:150,y:150}, SYN_SENT: {x:650,y:150},
    SYN_RCVD: {x:150,y:280}, ESTABLISHED: {x:400,y:280},
    FIN_WAIT_1: {x:650,y:280}, CLOSE_WAIT: {x:150,y:410},
    FIN_WAIT_2: {x:650,y:410}, CLOSING: {x:500,y:410},
    LAST_ACK: {x:150,y:540}, TIME_WAIT: {x:650,y:540},
};

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