VLANs, trunks and switch security

Python 3.14 · main.py

from zlib import crc32 as crc


def fcs(f: bytes) -> bytes:
    return crc(f).to_bytes(4, "little")


plain = bytes.fromhex("00005e00530200005e00530188b5") + b"hello, VLAN 10".ljust(
    46, b"\0"
)
tag = plain[:12] + bytes([129, 0, 160, 10]) + plain[12:]
tci = int.from_bytes(tag[14:16], "big")
for name, f in [("untagged", plain), ("tagged  ", tag)]:
    size = len(f)
    print(f"{name}: {size} bytes + FCS = {size + 4} bytes, FCS {fcs(f).hex(' ')}")
    print(f"  first 20 bytes: {f[:20].hex(' ')}")
print(
    f"tag read back: {{'pcp': {tci >> 13}, 'dei': {(tci >> 12) & 1}, 'vid': {tci & 4095}}}"
)
print(f"stripped frame equals the original: {tag[:12] + tag[16:] == plain}")
print(f"tagged and untagged FCS differ: {fcs(tag) != fcs(plain)}")
for name, f in [("untagged", plain), ("tagged", tag)]:
    print(f"receiver's check over {name} frame + FCS: {crc(f + fcs(f)):#010x}")

Recorded with CPython 3.14.8 on macOS 26 arm64. It runs in your browser with Pyodide 314.0.7 (CPython 3.14.2). To run it yourself: python3 main.py

JavaScript Node 24 · main.mjs

function crc(a) {
  let c = 0xffffffff;
  for (const b of a) {
    c ^= b;
    for (let j = 0; j < 8; j++) c = (c >>> 1) ^ (c & 1 ? 0xedb88320 : 0);
  }
  return (c ^ 0xffffffff) >>> 0;
}
const hex = (a) => a.map((b) => b.toString(16).padStart(2, "0")).join(" ");
const a = [0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181];
a.push(...Array.from("hello, VLAN 10", (c) => c.charCodeAt(0)), ...Array(32).fill(0));
const b = [...a.slice(0, 12), 129, 0, 160, 10, ...a.slice(12)];
const back = [...b.slice(0, 12), ...b.slice(16)],
  t = (b[14] << 8) | b[15];
const frames = [a, b],
  names = ["untagged", "tagged  "];
const sums = frames.map(crc),
  checks = frames.map((f, i) => {
    const n = f.length,
      c = sums[i];
    const tail = Array.from({ length: 4 }, (_, j) => (c >>> (8 * j)) & 255);
    console.log(`${names[i]}: ${n} bytes + FCS = ${n + 4} bytes, FCS ${hex(tail)}`);
    console.log(`  first 20 bytes: ${hex(f.slice(0, 20))}`);
    return crc([...f, ...tail]);
  });
console.log(`tag read back: {'pcp': ${t >>> 13}, 'dei': ${(t >>> 12) & 1}, 'vid': ${t & 4095}}`);
console.log(`stripped frame equals the original: ${hex(back) === hex(a) ? "True" : "False"}`);
console.log(`tagged and untagged FCS differ: ${sums[0] !== sums[1] ? "True" : "False"}`);
for (let i = 0; i < 2; i++) {
  const value = checks[i].toString(16).padStart(8, "0");
  console.log(`receiver's check over ${names[i].trim()} frame + FCS: 0x${value}`);
}

Recorded with Node.js 24.21.0 LTS (V8 13.6) on macOS 26 arm64. It runs in your browser with QuickJS (quickjs-emscripten 0.32.0). To run it yourself: node main.mjs

Java 25 LTS · Main.java

import java.util.Arrays;
import java.util.zip.CRC32;

public class Main {
  static int crc(byte[] a, int n) {
    var c = new CRC32();
    c.update(a, 0, n);
    return (int) c.getValue();
  }

  static String hex(byte[] a, int start, int n) {
    String[] r = new String[n];
    for (int i = 0; i < n; i++) r[i] = String.format("%02x", a[start + i] & 255);
    return String.join(" ", r);
  }

  public static void main(String[] args) {
    byte[] a = new byte[64], b = new byte[68], back = new byte[60];
    String head = "00005e00530200005e00530188b5";
    for (int i = 0; i < 14; i++)
      a[i] = (byte) Integer.parseInt(head.substring(2 * i, 2 * i + 2), 16);
    for (int i = 0; i < 14; i++) a[14 + i] = (byte) "hello, VLAN 10".charAt(i);
    System.arraycopy(a, 0, b, 0, 12);
    b[12] = (byte) 129;
    b[14] = (byte) 160;
    b[15] = 10;
    System.arraycopy(a, 12, b, 16, 48);
    System.arraycopy(b, 0, back, 0, 12);
    System.arraycopy(b, 16, back, 12, 48);
    byte[][] frames = {a, b};
    int[] sizes = {60, 64};
    String[] names = {"untagged", "tagged  "};
    int[] sums = new int[2], checks = new int[2];
    for (int i = 0; i < 2; i++) {
      byte[] f = frames[i];
      int n = sizes[i], c = crc(f, n);
      sums[i] = c;
      for (int j = 0; j < 4; j++) f[n + j] = (byte) (c >>> (8 * j));
      checks[i] = crc(f, n + 4);
      System.out.printf(
          "%s: %d bytes + FCS = %d bytes, FCS %s\n", names[i], n, n + 4, hex(f, n, 4));
      System.out.println("  first 20 bytes: " + hex(f, 0, 20));
    }
    int t = (b[14] & 255) << 8 | b[15] & 255;
    System.out.printf(
        "tag read back: {'pcp': %d, 'dei': %d, 'vid': %d}\n", t >>> 13, t >>> 12 & 1, t & 4095);
    System.out.printf(
        "stripped frame equals the original: %s\n",
        Arrays.equals(back, Arrays.copyOf(a, 60)) ? "True" : "False");
    System.out.printf(
        "tagged and untagged FCS differ: %s\n", sums[0] != sums[1] ? "True" : "False");
    for (int i = 0; i < 2; i++)
      System.out.printf(
          "receiver's check over %s frame + FCS: 0x%08x\n", names[i].trim(), checks[i]);
  }
}

Recorded with OpenJDK 25.0.4.1 LTS (Eclipse Temurin) on macOS 26 arm64. It runs in your browser with a TeaVM 0.16.0 build in QuickJS (quickjs-emscripten 0.32.0). To run it yourself: java Main.java

C++23 · main.cpp

#include <stdint.h>
#include <stdio.h>
#include <string.h>
unsigned crc(const unsigned char *a, int n) {
  unsigned c = ~0u;
  for (int i = 0; i < n; i++) {
    c ^= a[i];
    for (int j = 0; j < 8; j++)
      c = (c >> 1) ^ ((c & 1) ? 0xedb88320u : 0);
  }
  return ~c;
}
void hex(const unsigned char *a, int n) {
  for (int i = 0; i < n; i++)
    printf("%s%02x", i ? " " : "", a[i]);
}
int main(void) {
  unsigned char a[64] = {0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181},
                b[68] = {0}, back[60];
  memcpy(a + 14, "hello, VLAN 10", 14);
  memcpy(b, a, 12);
  b[12] = 129;
  b[14] = 160;
  b[15] = 10;
  memcpy(b + 16, a + 12, 48);
  memcpy(back, b, 12);
  memcpy(back + 12, b + 16, 48);
  unsigned char *frames[] = {a, b};
  int sizes[] = {60, 64};
  const char *names[] = {"untagged", "tagged  "};
  unsigned sums[2], checks[2];
  for (int i = 0; i < 2; i++) {
    int n = sizes[i];
    unsigned char *f = frames[i];
    unsigned c = crc(f, n);
    sums[i] = c;
    for (int j = 0; j < 4; j++)
      f[n + j] = (unsigned char)(c >> (8 * j));
    checks[i] = crc(f, n + 4);
    printf("%s: %d bytes + FCS = %d bytes, FCS ", names[i], n, n + 4);
    hex(f + n, 4);
    printf("\n  first 20 bytes: ");
    hex(f, 20);
    puts("");
  }
  unsigned t = (unsigned)b[14] << 8 | b[15];
  printf("tag read back: {'pcp': %u, 'dei': %u, 'vid': %u}\n", t >> 13,
         t >> 12 & 1, t & 4095);
  printf("stripped frame equals the original: %s\n",
         memcmp(back, a, 60) ? "False" : "True");
  printf("tagged and untagged FCS differ: %s\n",
         sums[0] != sums[1] ? "True" : "False");
  for (int i = 0; i < 2; i++)
    printf("receiver's check over %s frame + FCS: 0x%08x\n",
           i ? "tagged" : "untagged", checks[i]);
  return 0;
}

Recorded with Apple clang 21.0.0 (C++23) and GCC 16.2.0 on macOS 26 arm64. It runs in your browser with Clang in WebAssembly (YoWASP) 22.0.0-git20542-10. To run it yourself: clang++ -std=c++23 -O2 -Wall -Wextra -Werror -pedantic -fsanitize=address,undefined main.cpp -o main && ./main

C# 14 · .NET 10 · app.cs

static uint Crc(byte[] a, int n)
{
    uint c = uint.MaxValue;
    for (int i = 0; i < n; i++)
    {
        c ^= a[i];
        for (int j = 0; j < 8; j++) c = (c >> 1) ^ ((c & 1) == 1 ? 0xedb88320u : 0);
    }
    return ~c;
}
static string Hex(byte[] a, int from, int n) =>
    string.Join(" ", a.Skip(from).Take(n).Select(x => x.ToString("x2")));
byte[] a = new byte[64], b = new byte[68], back = new byte[60];
byte[] head = [0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181]; head.CopyTo(a, 0);
for (int i = 0; i < 14; i++) a[14 + i] = (byte)"hello, VLAN 10"[i];
Array.Copy(a, 0, b, 0, 12); b[12] = 129; b[14] = 160; b[15] = 10; Array.Copy(a, 12, b, 16, 48);
Array.Copy(b, 0, back, 0, 12); Array.Copy(b, 16, back, 12, 48);
byte[][] frames = [a, b]; int[] sizes = [60, 64]; string[] names = ["untagged", "tagged  "];
uint[] sums = new uint[2], checks = new uint[2];
for (int i = 0; i < 2; i++)
{
    byte[] f = frames[i]; int n = sizes[i]; uint c = Crc(f, n); sums[i] = c;
    for (int j = 0; j < 4; j++) f[n + j] = (byte)(c >> (8 * j)); checks[i] = Crc(f, n + 4);
    Console.WriteLine($"{names[i]}: {n} bytes + FCS = {n + 4} bytes, FCS {Hex(f, n, 4)}");
    Console.WriteLine($"  first 20 bytes: {Hex(f, 0, 20)}");
}
int t = b[14] << 8 | b[15];
Console.WriteLine($"tag read back: {{'pcp': {t >> 13}, 'dei': {t >> 12 & 1}, 'vid': {t & 4095}}}");
Console.WriteLine($"stripped frame equals the original: {back.SequenceEqual(a.Take(60))}");
Console.WriteLine($"tagged and untagged FCS differ: {sums[0] != sums[1]}");
for (int i = 0; i < 2; i++)
    Console.WriteLine($"receiver's check over {names[i].Trim()} frame + FCS: 0x{checks[i]:x8}");

Recorded with C# 14 on .NET 10.0.12 (SDK 10.0.401) on macOS 26 arm64. It runs in your browser with the .NET runtime for WebAssembly 10.0.12. To run it yourself: dotnet run app.cs

C23 · main.c

#include <stdint.h>
#include <stdio.h>
#include <string.h>
unsigned crc(const unsigned char *a, int n) {
  unsigned c = ~0u;
  for (int i = 0; i < n; i++) {
    c ^= a[i];
    for (int j = 0; j < 8; j++)
      c = (c >> 1) ^ ((c & 1) ? 0xedb88320u : 0);
  }
  return ~c;
}
void hex(const unsigned char *a, int n) {
  for (int i = 0; i < n; i++)
    printf("%s%02x", i ? " " : "", a[i]);
}
int main(void) {
  unsigned char a[64] = {0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181},
                b[68] = {0}, back[60];
  memcpy(a + 14, "hello, VLAN 10", 14);
  memcpy(b, a, 12);
  b[12] = 129;
  b[14] = 160;
  b[15] = 10;
  memcpy(b + 16, a + 12, 48);
  memcpy(back, b, 12);
  memcpy(back + 12, b + 16, 48);
  unsigned char *frames[] = {a, b};
  int sizes[] = {60, 64};
  const char *names[] = {"untagged", "tagged  "};
  unsigned sums[2], checks[2];
  for (int i = 0; i < 2; i++) {
    int n = sizes[i];
    unsigned char *f = frames[i];
    unsigned c = crc(f, n);
    sums[i] = c;
    for (int j = 0; j < 4; j++)
      f[n + j] = (unsigned char)(c >> (8 * j));
    checks[i] = crc(f, n + 4);
    printf("%s: %d bytes + FCS = %d bytes, FCS ", names[i], n, n + 4);
    hex(f + n, 4);
    printf("\n  first 20 bytes: ");
    hex(f, 20);
    puts("");
  }
  unsigned t = (unsigned)b[14] << 8 | b[15];
  printf("tag read back: {'pcp': %u, 'dei': %u, 'vid': %u}\n", t >> 13,
         t >> 12 & 1, t & 4095);
  printf("stripped frame equals the original: %s\n",
         memcmp(back, a, 60) ? "False" : "True");
  printf("tagged and untagged FCS differ: %s\n",
         sums[0] != sums[1] ? "True" : "False");
  for (int i = 0; i < 2; i++)
    printf("receiver's check over %s frame + FCS: 0x%08x\n",
           i ? "tagged" : "untagged", checks[i]);
  return 0;
}

Recorded with Apple clang 21.0.0 (C23) and GCC 16.2.0 on macOS 26 arm64. It runs in your browser with Clang in WebAssembly (YoWASP) 22.0.0-git20542-10. To run it yourself: clang -std=c23 -O2 -Wall -Wextra -Werror -pedantic -fsanitize=address,undefined main.c -o main && ./main

PHP 8.5 · main.php

<?php

declare(strict_types=1);

function hex(string $a): string
{
    return implode(' ', str_split(bin2hex($a), 2));
}
$a = hex2bin('00005e00530200005e00530188b5') . str_pad('hello, VLAN 10', 46, "\0");
$b = substr($a, 0, 12) . hex2bin('8100a00a') . substr($a, 12);
$back = substr($b, 0, 12) . substr($b, 16);
$t = ord($b[14]) << 8 | ord($b[15]);
$frames = [$a,$b];
$names = ['untagged','tagged'];
$sums = [];
$checks = [];
foreach ($frames as $i => $f) {
    $n = strlen($f);
    $c = crc32($f);
    $sums[] = $c;
    $tail = pack('V', $c);
    $checks[] = crc32($f . $tail);
    printf("%-8s: %d bytes + FCS = %d bytes, FCS %s\n", $names[$i], $n, $n + 4, hex($tail));
    echo '  first 20 bytes: ' . hex(substr($f, 0, 20)) . "\n";
}
printf("tag read back: {'pcp': %d, 'dei': %d, 'vid': %d}\n", $t >> 13, $t >> 12 & 1, $t & 4095);
echo 'stripped frame equals the original: ' . ($back === $a ? 'True' : 'False') . "\n";
echo 'tagged and untagged FCS differ: ' . ($sums[0] !== $sums[1] ? 'True' : 'False') . "\n";
foreach ($checks as $i => $c) {
    printf(
        "receiver's check over %s frame + FCS: 0x%s\n",
        $names[$i],
        bin2hex(pack('N', $c)),
    );
}

Recorded with PHP 8.5.11 (CLI) on macOS 26 arm64. It runs in your browser with php-wasm 0.2.0 (PHP 8.5.2). To run it yourself: php main.php

Rust 1.99 · main.rs

fn crc(a: &[u8]) -> u32 {
    let mut c = u32::MAX;
    for &b in a {
        c ^= u32::from(b);
        for _ in 0..8 {
            c = (c >> 1) ^ if c & 1 != 0 { 0xedb88320 } else { 0 }
        }
    }
    !c
}
fn hex(a: &[u8]) -> String {
    a.iter()
        .map(|b| format!("{b:02x}"))
        .collect::<Vec<_>>()
        .join(" ")
}
fn truth(v: bool) -> &'static str {
    if v { "True" } else { "False" }
}
fn main() {
    let mut a = vec![0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181];
    a.extend_from_slice(b"hello, VLAN 10");
    a.resize(60, 0);
    let mut b = a.clone();
    b.splice(12..12, [129, 0, 160, 10]);
    let back = [&b[..12], &b[16..]].concat();
    let t = u16::from_be_bytes([b[14], b[15]]);
    let frames = [a.clone(), b];
    let names = ["untagged", "tagged  "];
    let mut sums = [0; 2];
    let mut checks = [0; 2];
    for (i, f) in frames.iter().enumerate() {
        let n = f.len();
        let c = crc(f);
        sums[i] = c;
        let tail = c.to_le_bytes();
        println!(
            "{}: {n} bytes + FCS = {} bytes, FCS {}",
            names[i],
            n + 4,
            hex(&tail)
        );
        println!("  first 20 bytes: {}", hex(&f[..20]));
        checks[i] = crc(&[f.as_slice(), &tail].concat());
    }
    println!(
        "tag read back: {{'pcp': {}, 'dei': {}, 'vid': {}}}",
        t >> 13,
        t >> 12 & 1,
        t & 4095
    );
    println!("stripped frame equals the original: {}", truth(back == a));
    println!(
        "tagged and untagged FCS differ: {}",
        truth(sums[0] != sums[1])
    );
    for i in 0..2 {
        println!(
            "receiver's check over {} frame + FCS: 0x{:08x}",
            names[i].trim(),
            checks[i]
        );
    }
}

Recorded with rustc 1.99.0 (edition 2024) on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: rustc --edition 2024 -O main.rs && ./main

TypeScript 6.0 · main.ts

function crc(a: number[]): number {
  let c = 0xffffffff;
  for (const b of a) {
    c ^= b;
    for (let j = 0; j < 8; j++) c = (c >>> 1) ^ (c & 1 ? 0xedb88320 : 0);
  }
  return (c ^ 0xffffffff) >>> 0;
}
const hex = (a: number[]) => a.map((b) => b.toString(16).padStart(2, "0")).join(" ");
const a = [0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181];
a.push(...Array.from("hello, VLAN 10", (c) => c.charCodeAt(0)), ...Array(32).fill(0));
const b = [...a.slice(0, 12), 129, 0, 160, 10, ...a.slice(12)];
const back = [...b.slice(0, 12), ...b.slice(16)],
  t = (b[14] << 8) | b[15];
const frames = [a, b],
  names = ["untagged", "tagged  "];
const sums = frames.map(crc),
  checks = frames.map((f, i) => {
    const n = f.length,
      c = sums[i];
    const tail = Array.from({ length: 4 }, (_, j) => (c >>> (8 * j)) & 255);
    console.log(`${names[i]}: ${n} bytes + FCS = ${n + 4} bytes, FCS ${hex(tail)}`);
    console.log(`  first 20 bytes: ${hex(f.slice(0, 20))}`);
    return crc([...f, ...tail]);
  });
console.log(`tag read back: {'pcp': ${t >>> 13}, 'dei': ${(t >>> 12) & 1}, 'vid': ${t & 4095}}`);
console.log(`stripped frame equals the original: ${hex(back) === hex(a) ? "True" : "False"}`);
console.log(`tagged and untagged FCS differ: ${sums[0] !== sums[1] ? "True" : "False"}`);
for (let i = 0; i < 2; i++) {
  const value = checks[i].toString(16).padStart(8, "0");
  console.log(`receiver's check over ${names[i].trim()} frame + FCS: 0x${value}`);
}

Recorded with TypeScript 6.0.3 (strict), run by Node.js 24.21.0 on macOS 26 arm64. It runs in your browser with QuickJS (quickjs-emscripten 0.32.0) after Sucrase 3.35.1. To run it yourself: npx -p typescript@6.0.3 tsc --noEmit --strict main.ts && node main.ts

Go 1.27 · main.go

package main

import (
	"bytes"
	"fmt"
	"hash/crc32"
)

func truth(v bool) string {
	if v {
		return "True"
	}
	return "False"
}
func main() {
	a := make([]byte, 60)
	copy(a, []byte{0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181})
	copy(a[14:], "hello, VLAN 10")
	b := make([]byte, 64)
	copy(b, a[:12])
	copy(b[12:], []byte{129, 0, 160, 10})
	copy(b[16:], a[12:])
	back := append(append([]byte{}, b[:12]...), b[16:]...)
	t := uint16(b[14])<<8 | uint16(b[15])
	frames := [][]byte{a, b}
	names := []string{"untagged", "tagged"}
	var sums, checks [2]uint32
	for i, f := range frames {
		n := len(f)
		c := crc32.ChecksumIEEE(f)
		sums[i] = c
		tail := []byte{byte(c), byte(c >> 8), byte(c >> 16), byte(c >> 24)}
		checks[i] = crc32.ChecksumIEEE(append(f, tail...))
		fmt.Printf("%-8s: %d bytes + FCS = %d bytes, FCS % x\n", names[i], n, n+4, tail)
		fmt.Printf("  first 20 bytes: % x\n", f[:20])
	}
	fmt.Printf("tag read back: {'pcp': %d, 'dei': %d, 'vid': %d}\n", t>>13, t>>12&1, t&4095)
	fmt.Printf("stripped frame equals the original: %s\n", truth(bytes.Equal(back, a)))
	fmt.Printf("tagged and untagged FCS differ: %s\n", truth(sums[0] != sums[1]))
	for i, c := range checks {
		fmt.Printf("receiver's check over %s frame + FCS: 0x%08x\n", names[i], c)
	}
}

Recorded with Go 1.27.1 on macOS 26 arm64. It runs in your browser with the Go compiler in WebAssembly 1.27.1. To run it yourself: go run main.go

Swift 6.4 · main.swift

func crc(_ a: [UInt8]) -> UInt32 {
  var c = UInt32.max
  for b in a {
    c ^= UInt32(b)
    for _ in 0..<8 { c = (c >> 1) ^ (c & 1 != 0 ? 0xedb8_8320 : 0) }
  }
  return ~c
}
func hex(_ a: [UInt8]) -> String {
  a.map { String(Int($0) + 256, radix: 16).dropFirst() }.joined(separator: " ")
}
func truth(_ v: Bool) -> String { v ? "True" : "False" }
var a: [UInt8] = [0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181]
a += Array("hello, VLAN 10".utf8) + [UInt8](repeating: 0, count: 32)
let b = Array(a.prefix(12)) + [129, 0, 160, 10] + Array(a.dropFirst(12))
let back = Array(b.prefix(12)) + Array(b.dropFirst(16))
let t = UInt16(b[14]) << 8 | UInt16(b[15])
let frames = [a, b]
let names = ["untagged", "tagged  "]
var sums = [UInt32](repeating: 0, count: 2)
var checks = [UInt32](repeating: 0, count: 2)
for i in 0..<2 {
  let f = frames[i]
  let n = f.count
  let c = crc(f)
  sums[i] = c
  let tail = (0..<4).map { UInt8(truncatingIfNeeded: c >> ($0 * 8)) }
  print("\(names[i]): \(n) bytes + FCS = \(n+4) bytes, FCS \(hex(tail))")
  print("  first 20 bytes: \(hex(Array(f.prefix(20))))")
  checks[i] = crc(f + tail)
}
print("tag read back: {'pcp': \(t>>13), 'dei': \(t>>12&1), 'vid': \(t&4095)}")
print("stripped frame equals the original: \(truth(back==a))")
print("tagged and untagged FCS differ: \(truth(sums[0] != sums[1]))")
for i in 0..<2 {
  let s = String(checks[i], radix: 16)
  let value = String(repeating: "0", count: 8 - s.count) + s
  print("receiver's check over \(i==0 ? "untagged":"tagged") frame + FCS: 0x\(value)")
}

Recorded with Apple Swift 6.4 on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: swiftc -O main.swift -o main && ./main

Ruby 4.0 · main.rb

# frozen_string_literal: true

require 'zlib'

def hex(bytes)
  bytes.unpack1('H*').scan(/../).join(' ')
end

a = ['00005e00530200005e00530188b5'].pack('H*') + 'hello, VLAN 10'.ljust(46, "\0")
b = a[0, 12] + ['8100a00a'].pack('H*') + a[12..]
back = b[0, 12] + b[16..]
t = b[14, 2].unpack1('n')
frames = [a, b]
names = %w[untagged tagged]
sums = []
checks = []
frames.each_with_index do |frame, i|
  n = frame.bytesize
  sum = Zlib.crc32(frame)
  sums << sum
  tail = [sum].pack('V')
  checks << Zlib.crc32(frame + tail)
  puts format('%<s>-8s: %<n>d bytes + FCS = %<m>d bytes, FCS %<h>s',
              s: names[i], n: n, m: n + 4, h: hex(tail))
  puts "  first 20 bytes: #{hex(frame[0, 20])}"
end
puts format("tag read back: {'pcp': %<p>d, 'dei': %<d>d, 'vid': %<v>d}",
            p: t >> 13, d: (t >> 12) & 1, v: t & 4095)
puts "stripped frame equals the original: #{back == a ? 'True' : 'False'}"
puts "tagged and untagged FCS differ: #{sums[0] != sums[1] ? 'True' : 'False'}"
checks.each_with_index do |sum, i|
  puts format("receiver's check over %<s>s frame + FCS: 0x%<c>08x", s: names[i], c: sum)
end

Recorded with CRuby 4.0.7 on macOS 26 arm64. It runs in your browser with ruby.wasm 2.10.1 (Ruby 4.0.0). To run it yourself: ruby main.rb

Kotlin 2.4 · Main.kt

fun crc(a: List<Int>): UInt {
    var c = UInt.MAX_VALUE
    for (b in a) {
        c = c xor b.toUInt()
        repeat(8) { c = (c shr 1) xor if (c and 1u != 0u) 0xedb88320u else 0u }
    }
    return c.inv()
}

fun hex(a: List<Int>) = a.joinToString(" ") { it.toString(16).padStart(2, '0') }

fun main() {
    val head = listOf(0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181)
    val a = head + "hello, VLAN 10".map { it.code } + List(32) { 0 }
    val b = a.take(12) + listOf(129, 0, 160, 10) + a.drop(12)
    val back = b.take(12) + b.drop(16)
    val t = b[14] shl 8 or b[15]
    val frames = listOf(a, b)
    val names = listOf("untagged", "tagged  ")
    val sums = frames.map { crc(it) }
    val checks =
        frames.mapIndexed { i, f ->
            val tail = List(4) { j -> ((sums[i] shr (8 * j)) and 255u).toInt() }
            println("${names[i]}: ${f.size} bytes + FCS = ${f.size + 4} bytes, FCS ${hex(tail)}")
            println("  first 20 bytes: ${hex(f.take(20))}")
            crc(f + tail)
        }
    println("tag read back: {'pcp': ${t shr 13}, 'dei': ${(t shr 12) and 1}, 'vid': ${t and 4095}}")
    println("stripped frame equals the original: ${if (back == a) "True" else "False"}")
    println("tagged and untagged FCS differ: ${if (sums[0] != sums[1]) "True" else "False"}")
    for (i in 0..1) {
        val value = checks[i].toString(16).padStart(8, '0')
        println("receiver's check over ${names[i].trim()} frame + FCS: 0x$value")
    }
}

Recorded with Kotlin 2.4.20 on Java 25.0.4.1 on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: kotlinc Main.kt -include-runtime -d main.jar && java -jar main.jar

Dart 3.13 · main.dart

int crc32(List<int> bytes) {
  var crc = 0xffffffff;
  for (final byte in bytes) {
    crc ^= byte;
    for (var bit = 0; bit < 8; bit++) {
      crc = (crc >> 1) ^ ((crc & 1) == 1 ? 0xedb88320 : 0);
    }
  }
  return crc ^ 0xffffffff;
}

List<int> fcs(List<int> bytes) {
  final crc = crc32(bytes);
  return [for (var index = 0; index < 4; index++) (crc >> (8 * index)) & 255];
}

String hex(List<int> bytes) =>
    bytes.map((byte) => byte.toRadixString(16).padLeft(2, '0')).join(' ');
String truth(bool v) => v ? 'True' : 'False';
void main() {
  final plain = [0, 0, 94, 0, 83, 2, 0, 0, 94, 0, 83, 1, 136, 181];
  plain.addAll('hello, VLAN 10'.codeUnits);
  plain.addAll(List.filled(32, 0));
  final tag = [...plain.take(12), 129, 0, 160, 10, ...plain.skip(12)];
  final tci = (tag[14] << 8) | tag[15];
  final restored = [...tag.take(12), ...tag.skip(16)];
  for (final (name, f) in [('untagged', plain), ('tagged  ', tag)]) {
    final size = f.length;
    print('$name: $size bytes + FCS = ${size + 4} bytes, FCS ${hex(fcs(f))}');
    print('  first 20 bytes: ${hex(f.take(20).toList())}');
  }
  print(
    "tag read back: {'pcp': ${tci >> 13}, 'dei': ${(tci >> 12) & 1}, 'vid': ${tci & 4095}}",
  );
  print(
    'stripped frame equals the original: ${truth(hex(restored) == hex(plain))}',
  );
  print(
    'tagged and untagged FCS differ: ${truth(hex(fcs(tag)) != hex(fcs(plain)))}',
  );
  for (final (name, f) in [('untagged', plain), ('tagged', tag)]) {
    final residue = crc32([...f, ...fcs(f)]).toRadixString(16).padLeft(8, '0');
    print("receiver's check over $name frame + FCS: 0x$residue");
  }
}

Recorded with Dart 3.13.5 on macOS 26 arm64. It runs in your browser with a WebAssembly build by dart2wasm 3.13.5. To run it yourself: dart run main.dart

Python 3.14 · main.py

names = ["pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"]
vlans = [10, 20, 1, 10, 20, 99]
allowed = {1, 10, 20, 99}


def send(v: int, n: int) -> int:
    return -1 if v not in allowed else 0 if v == n else v


def receive(t: int, n: int) -> int:
    return n if t == 0 else t if t in allowed else -1


for n in [1, 99]:
    native = [1, n]
    print(f"native=1,{n}")
    for h in [0, 4, 2, 5]:
        s, v = h // 3, vlans[h]
        t = send(v, native[s])
        far = receive(t, native[1 - s])
        got = [
            names[i]
            for i in range(6)
            if i != h and vlans[i] == (v if i // 3 == s else far)
        ]
        wire = "blocked" if t < 0 else "untagged" if t == 0 else f"tagged:{t}"
        print(f"{names[h]} vlan={v} wire={wire} got={','.join(got) or 'none'}")

Recorded with CPython 3.14.8 on macOS 26 arm64. It runs in your browser with Pyodide 314.0.7 (CPython 3.14.2). To run it yourself: python3 main.py

JavaScript Node 24 · main.mjs

const names = ["pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"],
  vlans = [10, 20, 1, 10, 20, 99];
const allowed = new Set([1, 10, 20, 99]);
const send = (v, n) => (allowed.has(v) ? (v === n ? 0 : v) : null);
const receive = (t, n) => (t === 0 ? n : allowed.has(t) ? t : null);
for (const n of [1, 99]) {
  const native = [1, n];
  console.log(`native=1,${n}`);
  for (const h of [0, 4, 2, 5]) {
    const s = Math.trunc(h / 3),
      v = vlans[h],
      t = send(v, native[s]);
    const far = t === null ? null : receive(t, native[1 - s]);
    const got = names.filter((_, i) => i !== h && vlans[i] === (Math.trunc(i / 3) === s ? v : far));
    const wire = t === null ? "blocked" : t === 0 ? "untagged" : `tagged:${t}`;
    console.log(`${names[h]} vlan=${v} wire=${wire} got=${got.join(",") || "none"}`);
  }
}

Recorded with Node.js 24.21.0 LTS (V8 13.6) on macOS 26 arm64. It runs in your browser with QuickJS (quickjs-emscripten 0.32.0). To run it yourself: node main.mjs

Java 25 LTS · Main.java

public class Main {
  static boolean allowed(int v) {
    return v == 1 || v == 10 || v == 20 || v == 99;
  }

  static int send(int v, int n) {
    return allowed(v) ? v == n ? 0 : v : -1;
  }

  static int receive(int t, int n) {
    return t == 0 ? n : allowed(t) ? t : -1;
  }

  public static void main(String[] args) {
    String[] names = {"pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"};
    int[] vlans = {10, 20, 1, 10, 20, 99};
    for (int n : new int[] {1, 99}) {
      int[] nativeVlan = {1, n};
      System.out.printf("native=1,%d\n", n);
      for (int h : new int[] {0, 4, 2, 5}) {
        int s = h / 3, v = vlans[h], t = send(v, nativeVlan[s]);
        int far = receive(t, nativeVlan[1 - s]);
        String got = "";
        for (int i = 0; i < 6; i++)
          if (i != h && vlans[i] == (i / 3 == s ? v : far))
            got += (got.isEmpty() ? "" : ",") + names[i];
        String wire = t < 0 ? "blocked" : t == 0 ? "untagged" : "tagged:" + t;
        System.out.printf(
            "%s vlan=%d wire=%s got=%s\n", names[h], v, wire, got.isEmpty() ? "none" : got);
      }
    }
  }
}

Recorded with OpenJDK 25.0.4.1 LTS (Eclipse Temurin) on macOS 26 arm64. It runs in your browser with a TeaVM 0.16.0 build in QuickJS (quickjs-emscripten 0.32.0). To run it yourself: java Main.java

C++23 · main.cpp

#include <stdio.h>
int allowed(int v) { return v == 1 || v == 10 || v == 20 || v == 99; }
int send(int v, int n) { return allowed(v) ? v == n ? 0 : v : -1; }
int receive(int t, int n) { return t == 0 ? n : allowed(t) ? t : -1; }
int main(void) {
  const char *names[] = {"pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"};
  int vlans[] = {10, 20, 1, 10, 20, 99}, senders[] = {0, 4, 2, 5};
  for (int c = 0; c < 2; c++) {
    int n = c ? 99 : 1, native[] = {1, n};
    printf("native=1,%d\n", n);
    for (int k = 0; k < 4; k++) {
      int h = senders[k], s = h / 3, v = vlans[h], t = send(v, native[s]);
      int far = t < 0 ? -1 : receive(t, native[1 - s]), first = 1;
      char wire[20];
      if (t < 0)
        snprintf(wire, sizeof wire, "blocked");
      else if (t == 0)
        snprintf(wire, sizeof wire, "untagged");
      else
        snprintf(wire, sizeof wire, "tagged:%d", t);
      printf("%s vlan=%d wire=%s got=", names[h], v, wire);
      for (int i = 0; i < 6; i++)
        if (i != h && vlans[i] == (i / 3 == s ? v : far)) {
          printf("%s%s", first ? "" : ",", names[i]);
          first = 0;
        }
      puts(first ? "none" : "");
    }
  }
  return 0;
}

Recorded with Apple clang 21.0.0 (C++23) and GCC 16.2.0 on macOS 26 arm64. It runs in your browser with Clang in WebAssembly (YoWASP) 22.0.0-git20542-10. To run it yourself: clang++ -std=c++23 -O2 -Wall -Wextra -Werror -pedantic -fsanitize=address,undefined main.cpp -o main && ./main

C# 14 · .NET 10 · app.cs

string[] names = ["pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"];
int[] vlans = [10, 20, 1, 10, 20, 99];
HashSet<int> allowed = [1, 10, 20, 99];
int? Send(int v, int n) => allowed.Contains(v) ? v == n ? 0 : v : null;
int? Receive(int t, int n) => t == 0 ? n : allowed.Contains(t) ? t : null;
foreach (int n in new[] { 1, 99 })
{
    int[] nativeVlan = [1, n]; Console.WriteLine($"native=1,{n}");
    foreach (int h in new[] { 0, 4, 2, 5 })
    {
        int s = h / 3, v = vlans[h]; int? t = Send(v, nativeVlan[s]);
        int? far = t is null ? null : Receive(t.Value, nativeVlan[1 - s]);
        var got = Enumerable.Range(0, 6).Where(i =>
            i != h && vlans[i] == (i / 3 == s ? v : far)).Select(i => names[i]);
        string wire = t is null ? "blocked" : t == 0 ? "untagged" : $"tagged:{t}";
        string text = string.Join(",", got);
        Console.WriteLine($"{names[h]} vlan={v} wire={wire} got={(text == "" ? "none" : text)}");
    }
}

Recorded with C# 14 on .NET 10.0.12 (SDK 10.0.401) on macOS 26 arm64. It runs in your browser with the .NET runtime for WebAssembly 10.0.12. To run it yourself: dotnet run app.cs

C23 · main.c

#include <stdio.h>
int allowed(int v) { return v == 1 || v == 10 || v == 20 || v == 99; }
int send(int v, int n) { return allowed(v) ? v == n ? 0 : v : -1; }
int receive(int t, int n) { return t == 0 ? n : allowed(t) ? t : -1; }
int main(void) {
  const char *names[] = {"pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"};
  int vlans[] = {10, 20, 1, 10, 20, 99}, senders[] = {0, 4, 2, 5};
  for (int c = 0; c < 2; c++) {
    int n = c ? 99 : 1, native[] = {1, n};
    printf("native=1,%d\n", n);
    for (int k = 0; k < 4; k++) {
      int h = senders[k], s = h / 3, v = vlans[h], t = send(v, native[s]);
      int far = t < 0 ? -1 : receive(t, native[1 - s]), first = 1;
      char wire[20];
      if (t < 0)
        snprintf(wire, sizeof wire, "blocked");
      else if (t == 0)
        snprintf(wire, sizeof wire, "untagged");
      else
        snprintf(wire, sizeof wire, "tagged:%d", t);
      printf("%s vlan=%d wire=%s got=", names[h], v, wire);
      for (int i = 0; i < 6; i++)
        if (i != h && vlans[i] == (i / 3 == s ? v : far)) {
          printf("%s%s", first ? "" : ",", names[i]);
          first = 0;
        }
      puts(first ? "none" : "");
    }
  }
  return 0;
}

Recorded with Apple clang 21.0.0 (C23) and GCC 16.2.0 on macOS 26 arm64. It runs in your browser with Clang in WebAssembly (YoWASP) 22.0.0-git20542-10. To run it yourself: clang -std=c23 -O2 -Wall -Wextra -Werror -pedantic -fsanitize=address,undefined main.c -o main && ./main

PHP 8.5 · main.php

<?php

declare(strict_types=1);

$names = ['pc-a','pc-b','printer','pc-c','pc-d','camera'];
$vlans = [10,20,1,10,20,99];
function allowed(int $v): bool
{
    return in_array($v, [1,10,20,99], true);
}
function send(int $v, int $n): ?int
{
    return allowed($v) ? ($v === $n ? 0 : $v) : null;
}
function receive(int $t, int $n): ?int
{
    return $t === 0 ? $n : (allowed($t) ? $t : null);
}
foreach ([1,99] as $n) {
    $native = [1,$n];
    echo "native=1,$n\n";
    foreach ([0,4,2,5] as $h) {
        $s = intdiv($h, 3);
        $v = $vlans[$h];
        $t = send($v, $native[$s]);
        $far = $t === null ? null : receive($t, $native[1 - $s]);
        $got = [];
        for ($i = 0;$i < 6;++$i) {
            if ($i !== $h && $vlans[$i] === (intdiv($i, 3) === $s ? $v : $far)) {
                $got[] = $names[$i];
            }
        }
        $wire = $t === null ? 'blocked' : ($t === 0 ? 'untagged' : "tagged:$t");
        echo $names[$h] . " vlan=$v wire=$wire got=" . (implode(',', $got) ?: 'none') . "\n";
    }
}

Recorded with PHP 8.5.11 (CLI) on macOS 26 arm64. It runs in your browser with php-wasm 0.2.0 (PHP 8.5.2). To run it yourself: php main.php

Rust 1.99 · main.rs

fn allowed(v: i32) -> bool {
    [1, 10, 20, 99].contains(&v)
}
fn send(v: i32, n: i32) -> i32 {
    if !allowed(v) {
        -1
    } else if v == n {
        0
    } else {
        v
    }
}
fn receive(t: i32, n: i32) -> i32 {
    if t == 0 {
        n
    } else if allowed(t) {
        t
    } else {
        -1
    }
}
fn main() {
    let names = ["pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"];
    let vlans = [10, 20, 1, 10, 20, 99];
    for n in [1, 99] {
        let native = [1, n];
        println!("native=1,{n}");
        for h in [0, 4, 2, 5] {
            let s = h / 3;
            let v = vlans[h];
            let t = send(v, native[s]);
            let far = receive(t, native[1 - s]);
            let got = (0..6)
                .filter(|&i| i != h && vlans[i] == if i / 3 == s { v } else { far })
                .map(|i| names[i])
                .collect::<Vec<_>>()
                .join(",");
            let wire = match t {
                -1 => "blocked".into(),
                0 => "untagged".into(),
                _ => format!("tagged:{t}"),
            };
            println!(
                "{} vlan={v} wire={wire} got={}",
                names[h],
                if got.is_empty() { "none" } else { &got }
            );
        }
    }
}

Recorded with rustc 1.99.0 (edition 2024) on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: rustc --edition 2024 -O main.rs && ./main

TypeScript 6.0 · main.ts

const names = ["pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"],
  vlans = [10, 20, 1, 10, 20, 99];
const allowed = new Set([1, 10, 20, 99]);
const send = (v: number, n: number): number | null => (allowed.has(v) ? (v === n ? 0 : v) : null);
const receive = (t: number, n: number): number | null => (t === 0 ? n : allowed.has(t) ? t : null);
for (const n of [1, 99]) {
  const native = [1, n];
  console.log(`native=1,${n}`);
  for (const h of [0, 4, 2, 5]) {
    const s = Math.trunc(h / 3),
      v = vlans[h],
      t = send(v, native[s]);
    const far = t === null ? null : receive(t, native[1 - s]);
    const got = names.filter((_, i) => i !== h && vlans[i] === (Math.trunc(i / 3) === s ? v : far));
    const wire = t === null ? "blocked" : t === 0 ? "untagged" : `tagged:${t}`;
    console.log(`${names[h]} vlan=${v} wire=${wire} got=${got.join(",") || "none"}`);
  }
}

Recorded with TypeScript 6.0.3 (strict), run by Node.js 24.21.0 on macOS 26 arm64. It runs in your browser with QuickJS (quickjs-emscripten 0.32.0) after Sucrase 3.35.1. To run it yourself: npx -p typescript@6.0.3 tsc --noEmit --strict main.ts && node main.ts

Go 1.27 · main.go

package main

import (
	"fmt"
	"strings"
)

func allowed(v int) bool { return v == 1 || v == 10 || v == 20 || v == 99 }
func send(v, n int) int {
	if !allowed(v) {
		return -1
	}
	if v == n {
		return 0
	}
	return v
}
func receive(t, n int) int {
	if t == 0 {
		return n
	}
	if !allowed(t) {
		return -1
	}
	return t
}
func main() {
	names := []string{"pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"}
	vlans := []int{10, 20, 1, 10, 20, 99}
	for _, n := range []int{1, 99} {
		native := []int{1, n}
		fmt.Printf("native=1,%d\n", n)
		for _, h := range []int{0, 4, 2, 5} {
			s, v := h/3, vlans[h]
			t := send(v, native[s])
			far := receive(t, native[1-s])
			got := []string{}
			for i, name := range names {
				target := far
				if i/3 == s {
					target = v
				}
				if i != h && vlans[i] == target {
					got = append(got, name)
				}
			}
			wire := "blocked"
			if t == 0 {
				wire = "untagged"
			} else if t > 0 {
				wire = fmt.Sprint("tagged:", t)
			}
			text := strings.Join(got, ",")
			if text == "" {
				text = "none"
			}
			fmt.Printf("%s vlan=%d wire=%s got=%s\n", names[h], v, wire, text)
		}
	}
}

Recorded with Go 1.27.1 on macOS 26 arm64. It runs in your browser with the Go compiler in WebAssembly 1.27.1. To run it yourself: go run main.go

Swift 6.4 · main.swift

let names = ["pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera"]
let vlans = [10, 20, 1, 10, 20, 99]
let allowed: Set<Int> = [1, 10, 20, 99]
func send(_ v: Int, _ n: Int) -> Int? { allowed.contains(v) ? v == n ? 0 : v : nil }
func receive(_ t: Int, _ n: Int) -> Int? { t == 0 ? n : allowed.contains(t) ? t : nil }
for n in [1, 99] {
  let native = [1, n]
  print("native=1,\(n)")
  for h in [0, 4, 2, 5] {
    let s = h / 3
    let v = vlans[h]
    let t = send(v, native[s])
    let far = t.flatMap { receive($0, native[1 - s]) }
    let got = (0..<6).filter { $0 != h && vlans[$0] == ($0 / 3 == s ? v : far) }
      .map { names[$0] }.joined(separator: ",")
    let wire = t.map { $0 == 0 ? "untagged" : "tagged:\($0)" } ?? "blocked"
    print("\(names[h]) vlan=\(v) wire=\(wire) got=\(got.isEmpty ? "none":got)")
  }
}

Recorded with Apple Swift 6.4 on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: swiftc -O main.swift -o main && ./main

Ruby 4.0 · main.rb

# frozen_string_literal: true

def send_tag(vlan, native)
  return unless [1, 10, 20, 99].include?(vlan)

  vlan == native ? 0 : vlan
end

def receive(tag, native)
  if tag.zero?
    native
  else
    ([1, 10, 20, 99].include?(tag) ? tag : nil)
  end
end

names = %w[pc-a pc-b printer pc-c pc-d camera]
vlans = [10, 20, 1, 10, 20, 99]
[1, 99].each do |n|
  native = [1, n]
  puts "native=1,#{n}"
  [0, 4, 2, 5].each do |h|
    s = h / 3
    v = vlans[h]
    t = send_tag(v, native[s])
    far = receive(t, native[1 - s]) unless t.nil?
    got = (0...6).select { |i| i != h && vlans[i] == (i / 3 == s ? v : far) }
                 .map { |i| names[i] }.join(',')
    wire = if t.nil?
             'blocked'
           else
             t.zero? ? 'untagged' : "tagged:#{t}"
           end
    puts "#{names[h]} vlan=#{v} wire=#{wire} got=#{got.empty? ? 'none' : got}"
  end
end

Recorded with CRuby 4.0.7 on macOS 26 arm64. It runs in your browser with ruby.wasm 2.10.1 (Ruby 4.0.0). To run it yourself: ruby main.rb

Kotlin 2.4 · Main.kt

fun main() {
    val names = listOf("pc-a", "pc-b", "printer", "pc-c", "pc-d", "camera")
    val vlans = listOf(10, 20, 1, 10, 20, 99)
    val allowed = setOf(1, 10, 20, 99)

    fun send(
        v: Int,
        n: Int,
    ): Int =
        when {
            v !in allowed -> -1
            v == n -> 0
            else -> v
        }

    fun receive(
        t: Int,
        n: Int,
    ): Int =
        when {
            t == 0 -> n
            t in allowed -> t
            else -> -1
        }
    for (n in listOf(1, 99)) {
        val native = listOf(1, n)
        println("native=1,$n")
        for (h in listOf(0, 4, 2, 5)) {
            val s = h / 3
            val v = vlans[h]
            val t = send(v, native[s])
            val far = receive(t, native[1 - s])
            val got =
                (0..5)
                    .filter { it != h && vlans[it] == if (it / 3 == s) v else far }
                    .joinToString(",") { names[it] }
                    .ifEmpty { "none" }
            val wire =
                when (t) {
                    -1 -> "blocked"
                    0 -> "untagged"
                    else -> "tagged:$t"
                }
            println("${names[h]} vlan=$v wire=$wire got=$got")
        }
    }
}

Recorded with Kotlin 2.4.20 on Java 25.0.4.1 on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: kotlinc Main.kt -include-runtime -d main.jar && java -jar main.jar

Dart 3.13 · main.dart

void main() {
  final names = ['pc-a', 'pc-b', 'printer', 'pc-c', 'pc-d', 'camera'];
  final vlans = [10, 20, 1, 10, 20, 99], allowed = {1, 10, 20, 99};
  int send(int v, int n) {
    if (!allowed.contains(v)) return -1;
    return v == n ? 0 : v;
  }

  int receive(int t, int n) {
    if (t == 0) return n;
    return allowed.contains(t) ? t : -1;
  }

  for (final n in [1, 99]) {
    final native = [1, n];
    print('native=1,$n');
    for (final h in [0, 4, 2, 5]) {
      final s = h ~/ 3, v = vlans[h], t = send(v, native[s]);
      final far = receive(t, native[1 - s]);
      final got = [
        for (var i = 0; i < 6; i++)
          if (i != h && vlans[i] == (i ~/ 3 == s ? v : far)) names[i],
      ].join(',');
      final wire = t < 0
          ? 'blocked'
          : t == 0
          ? 'untagged'
          : 'tagged:$t';
      print('${names[h]} vlan=$v wire=$wire got=${got.isEmpty ? 'none' : got}');
    }
  }
}

Recorded with Dart 3.13.5 on macOS 26 arm64. It runs in your browser with a WebAssembly build by dart2wasm 3.13.5. To run it yourself: dart run main.dart

Python 3.14 · main.py

tab, ask, mac, cnt, off = {}, {}, {}, {}, set()


def step(event):
    t, p, src, msg, id, ip, ttl = event
    if p in off:
        return 0
    if p != 1:
        if p in mac and mac[p] != src:
            off.add(p)
            return 1
        mac[p] = src
    if msg:
        if p != 1:
            if msg >= 3:
                return 2
            if id != src:
                return 3
            ask[id] = p
            return 4
        if msg == 4 and id in ask:
            tab[ip] = (id, ask[id], ttl)
            return 5
        return 6
    if p == 1:
        return 7
    key = (p, t // 100)
    cnt[key] = cnt.get(key, 0) + 1
    if cnt[key] > 15:
        off.add(p)
        return 8
    entry = tab.get(ip)
    return 9 if entry is None else 10 if entry[:2] == (src, p) else 11


rowset = [
    [0, 2, 2, 1, 2, 0, 0],
    [10, 3, 102, 3, 2, -10, 0],
    [10, 1, 1, 3, 2, 25, 0],
    [20, 2, 2, 2, 2, 0, 0],
    [30, 1, 1, 4, 2, 25, 86400],
    [100, 2, 2, 0, 0, 25, 0],
    [100, 1, 1, 0, 0, 1, 0],
    [200, 3, 102, 0, 0, 1, 0],
    [250, 3, 102, 0, 0, 25, 0],
]
rowset += [[400 + 5 * i, 3, 102, 0, 0, 100 + i, 0] for i in range(20)]
rowset += [
    [600, 3, 102, 0, 0, 66, 0],
    [700, 4, 119, 1, 119, 0, 0],
    [750, 4, 120, 1, 120, 0, 0],
]
for event in rowset:
    print(step(event))
for ip, (src, p, ttl) in sorted(tab.items()):
    print(f"binding=192.168.10.{ip},00:00:5e:00:53:{src:02x},10,{p},{ttl}")

Recorded with CPython 3.14.8 on macOS 26 arm64. It runs in your browser with Pyodide 314.0.7 (CPython 3.14.2). To run it yourself: python3 main.py

JavaScript Node 24 · main.mjs

const ask = Array(256).fill(0),
  mac = Array(6).fill(0),
  off = Array(6).fill(false);
const cnt = Array.from({ length: 6 }, () => Array(10).fill(0)),
  tab = Array(256).fill(null);
function step([t, p, src, msg, id, ip, ttl]) {
  if (off[p]) return 0;
  if (p !== 1) {
    if (mac[p] && mac[p] !== src + 1) {
      off[p] = true;
      return 1;
    }
    mac[p] = src + 1;
  }
  if (msg) {
    if (p !== 1) {
      if (msg >= 3) return 2;
      if (id !== src) return 3;
      ask[id] = p;
      return 4;
    }
    if (msg === 4 && ask[id]) {
      tab[ip] = [id, ask[id], ttl];
      return 5;
    }
    return 6;
  }
  if (p === 1) return 7;
  if (++cnt[p][Math.trunc(t / 100)] > 15) {
    off[p] = true;
    return 8;
  }
  const b = tab[ip];
  return b === null || b === undefined ? 9 : b[0] === src && b[1] === p ? 10 : 11;
}
const rows = [
  [0, 2, 2, 1, 2, 0, 0],
  [10, 3, 102, 3, 2, -10, 0],
  [10, 1, 1, 3, 2, 25, 0],
  [20, 2, 2, 2, 2, 0, 0],
  [30, 1, 1, 4, 2, 25, 86400],
  [100, 2, 2, 0, 0, 25, 0],
  [100, 1, 1, 0, 0, 1, 0],
  [200, 3, 102, 0, 0, 1, 0],
  [250, 3, 102, 0, 0, 25, 0],
];
for (let i = 0; i < 20; i++) rows.push([400 + 5 * i, 3, 102, 0, 0, 100 + i, 0]);
rows.push([600, 3, 102, 0, 0, 66, 0], [700, 4, 119, 1, 119, 0, 0], [750, 4, 120, 1, 120, 0, 0]);
for (const e of rows) console.log(step(e));
for (let ip = 0; ip < 256; ip++)
  if (tab[ip]) {
    const [src, p, ttl] = tab[ip];
    console.log(
      `binding=192.168.10.${ip},00:00:5e:00:53:${src.toString(16).padStart(2, "0")},10,${p},${ttl}`,
    );
  }

Recorded with Node.js 24.21.0 LTS (V8 13.6) on macOS 26 arm64. It runs in your browser with QuickJS (quickjs-emscripten 0.32.0). To run it yourself: node main.mjs

Java 25 LTS · Main.java

public class Main {
  static final int[] ask = new int[256], mac = new int[6];
  static final int[][] cnt = new int[6][10], tab = new int[256][];
  static final boolean[] off = new boolean[6];

  static int step(int[] e) {
    int t = e[0], p = e[1], src = e[2], msg = e[3], id = e[4], ip = e[5], ttl = e[6];
    if (off[p]) return 0;
    if (p != 1) {
      if (mac[p] != 0 && mac[p] != src + 1) {
        off[p] = true;
        return 1;
      }
      mac[p] = src + 1;
    }
    if (msg != 0) {
      if (p != 1) {
        if (msg >= 3) return 2;
        if (id != src) return 3;
        ask[id] = p;
        return 4;
      }
      if (msg == 4 && ask[id] != 0) {
        tab[ip] = new int[] {id, ask[id], ttl};
        return 5;
      }
      return 6;
    }
    if (p == 1) return 7;
    if (++cnt[p][t / 100] > 15) {
      off[p] = true;
      return 8;
    }
    int[] b = tab[ip];
    return b == null ? 9 : b[0] == src && b[1] == p ? 10 : 11;
  }

  public static void main(String[] args) {
    String text =
        "0 2 2 1 2 0 0;10 3 102 3 2 -10 0;10 1 1 3 2 25 0;20 2 2 2 2 0 0;"
            + "30 1 1 4 2 25 86400;100 2 2 0 0 25 0;100 1 1 0 0 1 0;200 3 102 0 0 1 0;"
            + "250 3 102 0 0 25 0;600 3 102 0 0 66 0;700 4 119 1 119 0 0;750 4 120 1 120 0 0";
    var rows = new java.util.ArrayList<int[]>();
    for (String row : text.split(";"))
      rows.add(java.util.Arrays.stream(row.split(" ")).mapToInt(Integer::parseInt).toArray());
    for (int i = 0; i < 20; i++) rows.add(9 + i, new int[] {400 + 5 * i, 3, 102, 0, 0, 100 + i, 0});
    rows.forEach(e -> System.out.println(step(e)));
    for (int ip = 0; ip < 256; ip++)
      if (tab[ip] != null) {
        int[] b = tab[ip];
        System.out.printf(
            "binding=192.168.10.%d,00:00:5e:00:53:%02x,10,%d,%d%n", ip, b[0], b[1], b[2]);
      }
  }
}

Recorded with OpenJDK 25.0.4.1 LTS (Eclipse Temurin) on macOS 26 arm64. It runs in your browser with a TeaVM 0.16.0 build in QuickJS (quickjs-emscripten 0.32.0). To run it yourself: java Main.java

C++23 · main.cpp

#include <stdio.h>
static int tab[256][3], ask[256], mac[6], off[6], cnt[6][10];
static int step(const int *e) {
  int t = e[0], p = e[1], src = e[2], msg = e[3], id = e[4], ip = e[5],
      ttl = e[6];
  if (off[p])
    return 0;
  if (p != 1) {
    if (mac[p] && mac[p] != src + 1) {
      off[p] = 1;
      return 1;
    }
    mac[p] = src + 1;
  }
  if (msg) {
    if (p != 1) {
      if (msg >= 3)
        return 2;
      if (id != src)
        return 3;
      ask[id] = p;
      return 4;
    }
    if (msg == 4 && ask[id]) {
      tab[ip][0] = id;
      tab[ip][1] = ask[id];
      tab[ip][2] = ttl;
      return 5;
    }
    return 6;
  }
  if (p == 1)
    return 7;
  if (++cnt[p][t / 100] > 15) {
    off[p] = 1;
    return 8;
  }
  if (tab[ip][1] == 0)
    return 9;
  return tab[ip][0] == src && tab[ip][1] == p ? 10 : 11;
}
int main(void) {
  const int head[][7] = {
      {0, 2, 2, 1, 2, 0, 0},       {10, 3, 102, 3, 2, -10, 0},
      {10, 1, 1, 3, 2, 25, 0},     {20, 2, 2, 2, 2, 0, 0},
      {30, 1, 1, 4, 2, 25, 86400}, {100, 2, 2, 0, 0, 25, 0},
      {100, 1, 1, 0, 0, 1, 0},     {200, 3, 102, 0, 0, 1, 0},
      {250, 3, 102, 0, 0, 25, 0}};
  for (int i = 0; i < 9; i++)
    printf("%d\n", step(head[i]));
  for (int i = 0; i < 20; i++) {
    int e[] = {400 + 5 * i, 3, 102, 0, 0, 100 + i, 0};
    printf("%d\n", step(e));
  }
  const int tail[][7] = {{600, 3, 102, 0, 0, 66, 0},
                         {700, 4, 119, 1, 119, 0, 0},
                         {750, 4, 120, 1, 120, 0, 0}};
  for (int i = 0; i < 3; i++)
    printf("%d\n", step(tail[i]));
  for (int ip = 0; ip < 256; ip++)
    if (tab[ip][1] != 0)
      printf("binding=192.168.10.%d,00:00:5e:00:53:%02x,10,%d,%d\n", ip,
             tab[ip][0], tab[ip][1], tab[ip][2]);
  return 0;
}

Recorded with Apple clang 21.0.0 (C++23) and GCC 16.2.0 on macOS 26 arm64. It runs in your browser with Clang in WebAssembly (YoWASP) 22.0.0-git20542-10. To run it yourself: clang++ -std=c++23 -O2 -Wall -Wextra -Werror -pedantic -fsanitize=address,undefined main.cpp -o main && ./main

C# 14 · .NET 10 · app.cs

int[] ask = new int[256], mac = new int[6];
int[,] cnt = new int[6, 10];
int[]?[] tab = new int[256][];
bool[] off = new bool[6];
int Step(int[] e)
{
    int t = e[0], p = e[1], src = e[2], msg = e[3], id = e[4], ip = e[5], ttl = e[6];
    if (off[p]) return 0;
    if (p != 1)
    {
        if (mac[p] != 0 && mac[p] != src + 1) { off[p] = true; return 1; }
        mac[p] = src + 1;
    }
    if (msg != 0)
    {
        if (p != 1) { if (msg >= 3) return 2; if (id != src) return 3; ask[id] = p; return 4; }
        if (msg == 4 && ask[id] != 0) { tab[ip] = [id, ask[id], ttl]; return 5; }
        return 6;
    }
    if (p == 1) return 7;
    if (++cnt[p, t / 100] > 15) { off[p] = true; return 8; }
    var b = tab[ip]; return b is null ? 9 : b[0] == src && b[1] == p ? 10 : 11;
}
int[][] rows = [[0,2,2,1,2,0,0],[10,3,102,3,2,-10,0],[10,1,1,3,2,25,0],
    [20,2,2,2,2,0,0],[30,1,1,4,2,25,86400],[100,2,2,0,0,25,0],
    [100,1,1,0,0,1,0],[200,3,102,0,0,1,0],[250,3,102,0,0,25,0]];
foreach (var e in rows) Console.WriteLine(Step(e));
for (int i = 0; i < 20; i++) Console.WriteLine(Step([400 + 5 * i, 3, 102, 0, 0, 100 + i, 0]));
int[][] tail = [[600, 3, 102, 0, 0, 66, 0],
    [700, 4, 119, 1, 119, 0, 0], [750, 4, 120, 1, 120, 0, 0]];
foreach (var e in tail)
    Console.WriteLine(Step(e));
for (int ip = 0; ip < 256; ip++) if (tab[ip] is { } b)
    Console.WriteLine($"binding=192.168.10.{ip},00:00:5e:00:53:{b[0]:x2},10,{b[1]},{b[2]}");

Recorded with C# 14 on .NET 10.0.12 (SDK 10.0.401) on macOS 26 arm64. It runs in your browser with the .NET runtime for WebAssembly 10.0.12. To run it yourself: dotnet run app.cs

C23 · main.c

#include <stdio.h>
static int tab[256][3], ask[256], mac[6], off[6], cnt[6][10];
static int step(const int *e) {
  int t = e[0], p = e[1], src = e[2], msg = e[3], id = e[4], ip = e[5],
      ttl = e[6];
  if (off[p])
    return 0;
  if (p != 1) {
    if (mac[p] && mac[p] != src + 1) {
      off[p] = 1;
      return 1;
    }
    mac[p] = src + 1;
  }
  if (msg) {
    if (p != 1) {
      if (msg >= 3)
        return 2;
      if (id != src)
        return 3;
      ask[id] = p;
      return 4;
    }
    if (msg == 4 && ask[id]) {
      tab[ip][0] = id;
      tab[ip][1] = ask[id];
      tab[ip][2] = ttl;
      return 5;
    }
    return 6;
  }
  if (p == 1)
    return 7;
  if (++cnt[p][t / 100] > 15) {
    off[p] = 1;
    return 8;
  }
  if (tab[ip][1] == 0)
    return 9;
  return tab[ip][0] == src && tab[ip][1] == p ? 10 : 11;
}
int main(void) {
  const int head[][7] = {
      {0, 2, 2, 1, 2, 0, 0},       {10, 3, 102, 3, 2, -10, 0},
      {10, 1, 1, 3, 2, 25, 0},     {20, 2, 2, 2, 2, 0, 0},
      {30, 1, 1, 4, 2, 25, 86400}, {100, 2, 2, 0, 0, 25, 0},
      {100, 1, 1, 0, 0, 1, 0},     {200, 3, 102, 0, 0, 1, 0},
      {250, 3, 102, 0, 0, 25, 0}};
  for (int i = 0; i < 9; i++)
    printf("%d\n", step(head[i]));
  for (int i = 0; i < 20; i++) {
    int e[] = {400 + 5 * i, 3, 102, 0, 0, 100 + i, 0};
    printf("%d\n", step(e));
  }
  const int tail[][7] = {{600, 3, 102, 0, 0, 66, 0},
                         {700, 4, 119, 1, 119, 0, 0},
                         {750, 4, 120, 1, 120, 0, 0}};
  for (int i = 0; i < 3; i++)
    printf("%d\n", step(tail[i]));
  for (int ip = 0; ip < 256; ip++)
    if (tab[ip][1] != 0)
      printf("binding=192.168.10.%d,00:00:5e:00:53:%02x,10,%d,%d\n", ip,
             tab[ip][0], tab[ip][1], tab[ip][2]);
  return 0;
}

Recorded with Apple clang 21.0.0 (C23) and GCC 16.2.0 on macOS 26 arm64. It runs in your browser with Clang in WebAssembly (YoWASP) 22.0.0-git20542-10. To run it yourself: clang -std=c23 -O2 -Wall -Wextra -Werror -pedantic -fsanitize=address,undefined main.c -o main && ./main

PHP 8.5 · main.php

<?php

declare(strict_types=1);

$ask = array_fill(0, 256, 0);
$mac = array_fill(0, 6, 0);
$off = array_fill(0, 6, false);
$cnt = array_fill(0, 6, array_fill(0, 10, 0));
$tab = array_fill(0, 256, [0,0,0]);
function step(array $e): int
{
    global $ask,$mac,$off,$cnt,$tab;
    [$t,$p,$src,$msg,$id,$ip,$ttl] = $e;
    if ($off[$p]) {
        return 0;
    }
    if ($p !== 1) {
        if ($mac[$p] !== 0 && $mac[$p] !== $src + 1) {
            $off[$p] = true;
            return 1;
        }$mac[$p] = $src + 1;
    }
    if ($msg !== 0) {
        if ($p !== 1) {
            if ($msg >= 3) {
                return 2;
            }if ($id !== $src) {
                return 3;
            }$ask[$id] = $p;
            return 4;
        }
        if ($msg === 4 && $ask[$id] !== 0) {
            $tab[$ip] = [$id,$ask[$id],$ttl];
            return 5;
        }return 6;
    }
    if ($p === 1) {
        return 7;
    }
    if (++$cnt[$p][intdiv($t, 100)] > 15) {
        $off[$p] = true;
        return 8;
    }
    $b = $tab[$ip];
    return $b[1] === 0 ? 9 : ($b[0] === $src && $b[1] === $p ? 10 : 11);
}
$rows = [[0,2,2,1,2,0,0],[10,3,102,3,2,-10,0],[10,1,1,3,2,25,0],
    [20,2,2,2,2,0,0],[30,1,1,4,2,25,86400],[100,2,2,0,0,25,0],
    [100,1,1,0,0,1,0],[200,3,102,0,0,1,0],[250,3,102,0,0,25,0]];
foreach ($rows as $e) {
    echo step($e) . "\n";
}
for ($i = 0;$i < 20;++$i) {
    echo step([400 + 5 * $i,3,102,0,0,100 + $i,0]) . "\n";
}
foreach ([[600,3,102,0,0,66,0],[700,4,119,1,119,0,0],[750,4,120,1,120,0,0]] as $e) {
    echo step($e) . "\n";
}
foreach ($tab as $ip => $b) {
    if ($b[1] !== 0) {
        printf("binding=192.168.10.%d,00:00:5e:00:53:%02x,10,%d,%d\n", $ip, $b[0], $b[1], $b[2]);
    }
}

Recorded with PHP 8.5.11 (CLI) on macOS 26 arm64. It runs in your browser with php-wasm 0.2.0 (PHP 8.5.2). To run it yourself: php main.php

Rust 1.99 · main.rs

fn main() {
    let mut ask = [0; 256];
    let mut mac = [0; 6];
    let mut off = [false; 6];
    let mut cnt = [[0; 10]; 6];
    let mut tab = [[0; 3]; 256];
    let mut rows = vec![
        [0, 2, 2, 1, 2, 0, 0],
        [10, 3, 102, 3, 2, -10, 0],
        [10, 1, 1, 3, 2, 25, 0],
        [20, 2, 2, 2, 2, 0, 0],
        [30, 1, 1, 4, 2, 25, 86400],
        [100, 2, 2, 0, 0, 25, 0],
        [100, 1, 1, 0, 0, 1, 0],
        [200, 3, 102, 0, 0, 1, 0],
        [250, 3, 102, 0, 0, 25, 0],
    ];
    rows.extend((0..20).map(|i| [400 + 5 * i, 3, 102, 0, 0, 100 + i, 0]));
    rows.extend([
        [600, 3, 102, 0, 0, 66, 0],
        [700, 4, 119, 1, 119, 0, 0],
        [750, 4, 120, 1, 120, 0, 0],
    ]);
    let mut step = |[t, p, src, msg, id, ip, ttl]: [i32; 7]| {
        let p = p as usize;
        let id = id as usize;
        if off[p] {
            return 0;
        }
        if p != 1 {
            if mac[p] != 0 && mac[p] != src + 1 {
                off[p] = true;
                return 1;
            }
            mac[p] = src + 1;
        }
        if msg != 0 {
            if p != 1 {
                if msg >= 3 {
                    return 2;
                }
                if id as i32 != src {
                    return 3;
                }
                ask[id] = p;
                return 4;
            }
            if msg == 4 && ask[id] != 0 {
                tab[ip as usize] = [id as i32, ask[id] as i32, ttl];
                return 5;
            }
            return 6;
        }
        if p == 1 {
            return 7;
        }
        cnt[p][(t / 100) as usize] += 1;
        if cnt[p][(t / 100) as usize] > 15 {
            off[p] = true;
            return 8;
        }
        let b = tab[ip as usize];
        if b[1] == 0 {
            9
        } else if b[0] == src && b[1] == p as i32 {
            10
        } else {
            11
        }
    };
    for e in rows {
        println!("{}", step(e));
    }
    for (ip, b) in tab.iter().enumerate().filter(|(_, b)| b[1] != 0) {
        println!(
            "binding=192.168.10.{ip},00:00:5e:00:53:{:02x},10,{},{}",
            b[0], b[1], b[2]
        );
    }
}

Recorded with rustc 1.99.0 (edition 2024) on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: rustc --edition 2024 -O main.rs && ./main

TypeScript 6.0 · main.ts

const ask = Array(256).fill(0),
  mac = Array(6).fill(0),
  off = Array(6).fill(false);
const cnt = Array.from({ length: 6 }, () => Array(10).fill(0)),
  tab: (number[] | null)[] = Array(256).fill(null);
function step([t, p, src, msg, id, ip, ttl]: number[]): number {
  if (off[p]) return 0;
  if (p !== 1) {
    if (mac[p] && mac[p] !== src + 1) {
      off[p] = true;
      return 1;
    }
    mac[p] = src + 1;
  }
  if (msg) {
    if (p !== 1) {
      if (msg >= 3) return 2;
      if (id !== src) return 3;
      ask[id] = p;
      return 4;
    }
    if (msg === 4 && ask[id]) {
      tab[ip] = [id, ask[id], ttl];
      return 5;
    }
    return 6;
  }
  if (p === 1) return 7;
  if (++cnt[p][Math.trunc(t / 100)] > 15) {
    off[p] = true;
    return 8;
  }
  const b = tab[ip];
  return b === null || b === undefined ? 9 : b[0] === src && b[1] === p ? 10 : 11;
}
const rows = [
  [0, 2, 2, 1, 2, 0, 0],
  [10, 3, 102, 3, 2, -10, 0],
  [10, 1, 1, 3, 2, 25, 0],
  [20, 2, 2, 2, 2, 0, 0],
  [30, 1, 1, 4, 2, 25, 86400],
  [100, 2, 2, 0, 0, 25, 0],
  [100, 1, 1, 0, 0, 1, 0],
  [200, 3, 102, 0, 0, 1, 0],
  [250, 3, 102, 0, 0, 25, 0],
];
for (let i = 0; i < 20; i++) rows.push([400 + 5 * i, 3, 102, 0, 0, 100 + i, 0]);
rows.push([600, 3, 102, 0, 0, 66, 0], [700, 4, 119, 1, 119, 0, 0], [750, 4, 120, 1, 120, 0, 0]);
for (const e of rows) console.log(step(e));
for (let ip = 0; ip < 256; ip++)
  if (tab[ip]) {
    const b = tab[ip];
    if (b === null) continue;
    const [src, p, ttl] = b;
    console.log(
      `binding=192.168.10.${ip},00:00:5e:00:53:${src.toString(16).padStart(2, "0")},10,${p},${ttl}`,
    );
  }

Recorded with TypeScript 6.0.3 (strict), run by Node.js 24.21.0 on macOS 26 arm64. It runs in your browser with QuickJS (quickjs-emscripten 0.32.0) after Sucrase 3.35.1. To run it yourself: npx -p typescript@6.0.3 tsc --noEmit --strict main.ts && node main.ts

Go 1.27 · main.go

package main

import "fmt"

var ask [256]int
var mac [6]int
var off [6]bool
var cnt [6][10]int
var tab [256][3]int

func step(e [7]int) int {
	t, p, src, msg, id, ip, ttl := e[0], e[1], e[2], e[3], e[4], e[5], e[6]
	if off[p] {
		return 0
	}
	if p != 1 {
		if mac[p] != 0 && mac[p] != src+1 {
			off[p] = true
			return 1
		}
		mac[p] = src + 1
	}
	if msg != 0 {
		if p != 1 {
			if msg >= 3 {
				return 2
			}
			if id != src {
				return 3
			}
			ask[id] = p
			return 4
		}
		if msg == 4 && ask[id] != 0 {
			tab[ip] = [3]int{id, ask[id], ttl}
			return 5
		}
		return 6
	}
	if p == 1 {
		return 7
	}
	cnt[p][t/100]++
	if cnt[p][t/100] > 15 {
		off[p] = true
		return 8
	}
	b := tab[ip]
	if b[1] == 0 {
		return 9
	}
	if b[0] == src && b[1] == p {
		return 10
	}
	return 11
}
func main() {
	rows := [][7]int{{0, 2, 2, 1, 2, 0, 0}, {10, 3, 102, 3, 2, -10, 0}, {10, 1, 1, 3, 2, 25, 0},
		{20, 2, 2, 2, 2, 0, 0}, {30, 1, 1, 4, 2, 25, 86400}, {100, 2, 2, 0, 0, 25, 0},
		{100, 1, 1, 0, 0, 1, 0}, {200, 3, 102, 0, 0, 1, 0}, {250, 3, 102, 0, 0, 25, 0}}
	for _, e := range rows {
		fmt.Println(step(e))
	}
	for i := 0; i < 20; i++ {
		fmt.Println(step([7]int{400 + 5*i, 3, 102, 0, 0, 100 + i, 0}))
	}
	for _, e := range [][7]int{{600, 3, 102, 0, 0, 66, 0},
		{700, 4, 119, 1, 119, 0, 0}, {750, 4, 120, 1, 120, 0, 0}} {
		fmt.Println(step(e))
	}
	for ip, b := range tab {
		if b[1] != 0 {
			fmt.Printf("binding=192.168.10.%d,00:00:5e:00:53:%02x,10,%d,%d\n", ip, b[0], b[1], b[2])
		}
	}
}

Recorded with Go 1.27.1 on macOS 26 arm64. It runs in your browser with the Go compiler in WebAssembly 1.27.1. To run it yourself: go run main.go

Swift 6.4 · main.swift

var ask = [Int](repeating: 0, count: 256)
var mac = [Int](repeating: 0, count: 6)
var off = [Bool](repeating: false, count: 6)
var cnt = [[Int]](repeating: [Int](repeating: 0, count: 10), count: 6)
var tab = [[Int]](repeating: [0, 0, 0], count: 256)
func step(_ e: [Int]) -> Int {
  let t = e[0]
  let p = e[1]
  let src = e[2]
  let msg = e[3]
  let id = e[4]
  let ip = e[5]
  let ttl = e[6]
  if off[p] { return 0 }
  if p != 1 {
    if mac[p] != 0 && mac[p] != src + 1 {
      off[p] = true
      return 1
    }
    mac[p] = src + 1
  }
  if msg != 0 {
    if p != 1 {
      if msg >= 3 { return 2 }
      if id != src { return 3 }
      ask[id] = p
      return 4
    }
    if msg == 4 && ask[id] != 0 {
      tab[ip] = [id, ask[id], ttl]
      return 5
    }
    return 6
  }
  if p == 1 { return 7 }
  cnt[p][t / 100] += 1
  if cnt[p][t / 100] > 15 {
    off[p] = true
    return 8
  }
  let b = tab[ip]
  return b[1] == 0 ? 9 : b[0] == src && b[1] == p ? 10 : 11
}
let rows = [
  [0, 2, 2, 1, 2, 0, 0], [10, 3, 102, 3, 2, -10, 0], [10, 1, 1, 3, 2, 25, 0],
  [20, 2, 2, 2, 2, 0, 0], [30, 1, 1, 4, 2, 25, 86400], [100, 2, 2, 0, 0, 25, 0],
  [100, 1, 1, 0, 0, 1, 0], [200, 3, 102, 0, 0, 1, 0], [250, 3, 102, 0, 0, 25, 0],
]
for e in rows { print(step(e)) }
for i in 0..<20 { print(step([400 + 5 * i, 3, 102, 0, 0, 100 + i, 0])) }
for e in [[600, 3, 102, 0, 0, 66, 0], [700, 4, 119, 1, 119, 0, 0], [750, 4, 120, 1, 120, 0, 0]] {
  print(step(e))
}
for ip in 0..<256 where tab[ip][1] != 0 {
  let b = tab[ip]
  let s = String(b[0], radix: 16)
  let hex = s.count == 1 ? "0" + s : s
  print("binding=192.168.10.\(ip),00:00:5e:00:53:\(hex),10,\(b[1]),\(b[2])")
}

Recorded with Apple Swift 6.4 on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: swiftc -O main.swift -o main && ./main

Ruby 4.0 · main.rb

# frozen_string_literal: true

def request(ask, row)
  _, port, src, msg, who, = row
  return 2 if msg >= 3
  return 3 if who != src

  ask[who] = port
  4
end

def dhcp(state, row)
  tab, ask = state
  _, port, _, msg, who, ip, ttl = row
  return request(ask, row) if port != 1
  return 6 unless msg == 4 && ask.key?(who)

  tab[ip] = [who, ask[who], ttl]
  5
end

def arp(state, row)
  tab, _, _, cnt, off = state
  ticks, port, src, _, _, ip = row
  return 7 if port == 1

  key = [port, ticks / 100]
  cnt[key] = cnt.fetch(key, 0) + 1
  return (off[port] = true) && 8 if cnt[key] > 15
  return 9 unless tab.key?(ip)

  tab[ip].first(2) == [src, port] ? 10 : 11
end

def security(state, port, src)
  _, _, mac, _, off = state
  return false if port == 1

  old = mac[port]
  return off[port] = true if old && old != src

  mac[port] = src
  false
end

def step(state, row)
  _, port, src, msg = row
  return 0 if state[4][port]
  return 1 if security(state, port, src)

  msg.zero? ? arp(state, row) : dhcp(state, row)
end

rows = [[0, 2, 2, 1, 2, 0, 0], [10, 3, 102, 3, 2, -10, 0], [10, 1, 1, 3, 2, 25, 0],
        [20, 2, 2, 2, 2, 0, 0], [30, 1, 1, 4, 2, 25, 86_400], [100, 2, 2, 0, 0, 25, 0],
        [100, 1, 1, 0, 0, 1, 0], [200, 3, 102, 0, 0, 1, 0], [250, 3, 102, 0, 0, 25, 0]]
rows += (0...20).map { |i| [400 + 5 * i, 3, 102, 0, 0, 100 + i, 0] }
rows += [[600, 3, 102, 0, 0, 66, 0], [700, 4, 119, 1, 119, 0, 0], [750, 4, 120, 1, 120, 0, 0]]
state = [{}, {}, {}, {}, {}]
rows.each { |row| puts step(state, row) }
state[0].keys.sort.each do |ip|
  mac, port, ttl = state[0][ip]
  suffix = mac.to_s(16).rjust(2, '0')
  puts "binding=192.168.10.#{ip},00:00:5e:00:53:#{suffix},10,#{port},#{ttl}"
end

Recorded with CRuby 4.0.7 on macOS 26 arm64. It runs in your browser with ruby.wasm 2.10.1 (Ruby 4.0.0). To run it yourself: ruby main.rb

Kotlin 2.4 · Main.kt

val ask = IntArray(256)
val mac = IntArray(6)
val off = BooleanArray(6)
val cnt = Array(6) { IntArray(10) }
val tab = Array(256) { IntArray(3) }

fun step(e: List<Int>): Int {
    val(t, p, src, msg, id) = e
    val ip = e[5]
    val ttl = e[6]
    if (off[p]) return 0
    if (p != 1) {
        if (mac[p] != 0 && mac[p] != src + 1) {
            off[p] = true
            return 1
        }
        mac[p] = src + 1
    }
    if (msg != 0) {
        if (p != 1) {
            if (msg >= 3) return 2
            if (id != src) return 3
            ask[id] = p
            return 4
        }
        if (msg == 4 && ask[id] != 0) {
            tab[ip] = intArrayOf(id, ask[id], ttl)
            return 5
        }
        return 6
    }
    if (p == 1) return 7
    if (++cnt[p][t / 100] > 15) {
        off[p] = true
        return 8
    }
    val b = tab[ip]
    return if (b[1] == 0) {
        9
    } else if (b[0] == src && b[1] == p) {
        10
    } else {
        11
    }
}

fun main() {
    val text =
        "0 2 2 1 2 0 0;10 3 102 3 2 -10 0;10 1 1 3 2 25 0;20 2 2 2 2 0 0;" +
            "30 1 1 4 2 25 86400;100 2 2 0 0 25 0;100 1 1 0 0 1 0;" +
            "200 3 102 0 0 1 0;250 3 102 0 0 25 0;600 3 102 0 0 66 0;" +
            "700 4 119 1 119 0 0;750 4 120 1 120 0 0"
    val rows = text.split(';').map { it.split(' ').map(String::toInt) }.toMutableList()
    rows.addAll(9, (0..19).map { i -> listOf(400 + 5 * i, 3, 102, 0, 0, 100 + i, 0) })
    for (e in rows)println(step(e))
    for (ip in tab.indices) {
        if (tab[ip][1] != 0) {
            val b = tab[ip]
            val suffix = b[0].toString(16).padStart(2, '0')
            println("binding=192.168.10.$ip,00:00:5e:00:53:$suffix,10,${b[1]},${b[2]}")
        }
    }
}

Recorded with Kotlin 2.4.20 on Java 25.0.4.1 on macOS 26 arm64. It runs in your browser with a WebAssembly build on the WASI runner (browser_wasi_shim 0.4.2). To run it yourself: kotlinc Main.kt -include-runtime -d main.jar && java -jar main.jar

Dart 3.13 · main.dart

void main() {
  final ask = List.filled(256, 0),
      mac = List.filled(6, 0),
      off = List.filled(6, false);
  final cnt = List.generate(6, (_) => List.filled(10, 0)),
      tab = List.generate(256, (_) => List.filled(3, 0));
  int step(List<int> e) {
    final [t, p, src, msg, id, ip, ttl] = e;
    if (off[p]) return 0;
    if (p != 1) {
      if (mac[p] != 0 && mac[p] != src + 1) {
        off[p] = true;
        return 1;
      }
      mac[p] = src + 1;
    }
    if (msg != 0) {
      if (p != 1) {
        if (msg >= 3) return 2;
        if (id != src) return 3;
        ask[id] = p;
        return 4;
      }
      if (msg == 4 && ask[id] != 0) {
        tab[ip] = [id, ask[id], ttl];
        return 5;
      }
      return 6;
    }
    if (p == 1) return 7;
    if (++cnt[p][t ~/ 100] > 15) {
      off[p] = true;
      return 8;
    }
    final b = tab[ip];
    return b[1] == 0
        ? 9
        : b[0] == src && b[1] == p
        ? 10
        : 11;
  }

  final rows = [
    [0, 2, 2, 1, 2, 0, 0],
    [10, 3, 102, 3, 2, -10, 0],
    [10, 1, 1, 3, 2, 25, 0],
    [20, 2, 2, 2, 2, 0, 0],
    [30, 1, 1, 4, 2, 25, 86400],
    [100, 2, 2, 0, 0, 25, 0],
    [100, 1, 1, 0, 0, 1, 0],
    [200, 3, 102, 0, 0, 1, 0],
    [250, 3, 102, 0, 0, 25, 0],
  ];
  for (final e in rows) print(step(e));
  for (var i = 0; i < 20; i++)
    print(step([400 + 5 * i, 3, 102, 0, 0, 100 + i, 0]));
  for (final e in [
    [600, 3, 102, 0, 0, 66, 0],
    [700, 4, 119, 1, 119, 0, 0],
    [750, 4, 120, 1, 120, 0, 0],
  ])
    print(step(e));
  for (var ip = 0; ip < 256; ip++)
    if (tab[ip][1] != 0) {
      final b = tab[ip], suffix = tab[ip][0].toRadixString(16).padLeft(2, '0');
      print('binding=192.168.10.$ip,00:00:5e:00:53:$suffix,10,${b[1]},${b[2]}');
    }
}

Recorded with Dart 3.13.5 on macOS 26 arm64. It runs in your browser with a WebAssembly build by dart2wasm 3.13.5. To run it yourself: dart run main.dart