while ($linha=mysql_fetch_array($resultado))
{
  echo "<tr>";
  echo "<td scope=\"col\">$linha[ip]</td>";
  echo "<td scope=\"col\">$linha[mac]</td>";
  echo "<td scope=\"col\"><a href='alterar.php?id={$linha[id]}'>Alterar</a></td>";
  echo "<td scope=\"col\">$linha[ativo]</td>";
  echo "<td scope=\"col\"><a href='excluir.php?id={$linha[id]}'>Excluir</a></td>";
  echo "</tr>";
}