\documentclass[10pt,a4paper]{article}

% Packages
\usepackage{fancyhdr}           % For header and footer
\usepackage{multicol}           % Allows multicols in tables
\usepackage{tabularx}           % Intelligent column widths
\usepackage{tabulary}           % Used in header and footer
\usepackage{hhline}             % Border under tables
\usepackage{graphicx}           % For images
\usepackage{xcolor}             % For hex colours
%\usepackage[utf8x]{inputenc}    % For unicode character support
\usepackage[T1]{fontenc}        % Without this we get weird character replacements
\usepackage{colortbl}           % For coloured tables
\usepackage{setspace}           % For line height
\usepackage{lastpage}           % Needed for total page number
\usepackage{seqsplit}           % Splits long words.
%\usepackage{opensans}          % Can't make this work so far. Shame. Would be lovely.
\usepackage[normalem]{ulem}     % For underlining links
% Most of the following are not required for the majority
% of cheat sheets but are needed for some symbol support.
\usepackage{amsmath}            % Symbols
\usepackage{MnSymbol}           % Symbols
\usepackage{wasysym}            % Symbols
%\usepackage[english,german,french,spanish,italian]{babel}              % Languages

% Document Info
\author{xavierjackson55}
\pdfinfo{
  /Title (lan-switching.pdf)
  /Creator (Cheatography)
  /Author (xavierjackson55)
  /Subject (LAN Switching Cheat Sheet)
}

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\renewcommand{\seqinsert}{\ifmmode\allowbreak\else\-\fi} % Hyphens in seqsplit
% This two commands together give roughly
% the right line height in the tables
\renewcommand{\arraystretch}{1.3}
\onehalfspacing

% Commands
\newcommand{\SetRowColor}[1]{\noalign{\gdef\RowColorName{#1}}\rowcolor{\RowColorName}} % Shortcut for row colour
\newcommand{\mymulticolumn}[3]{\multicolumn{#1}{>{\columncolor{\RowColorName}}#2}{#3}} % For coloured multi-cols
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\newcommand{\tn}{\tabularnewline} % Required as custom column type in use

% Font and Colours
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\renewcommand{\familydefault}{\sfdefault}
\color{TextColor}

% Header and Footer
\pagestyle{fancy}
\fancyhead{} % Set header to blank
\fancyfoot{} % Set footer to blank
\fancyhead[L]{
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{C}
    \SetRowColor{DarkBackground}
    \vspace{-7pt}
    {\parbox{\dimexpr\textwidth-2\fboxsep\relax}{\noindent
        \hspace*{-6pt}\includegraphics[width=5.8cm]{/web/www.cheatography.com/public/images/cheatography_logo.pdf}}
    }
\end{tabulary}
\columnbreak
\begin{tabulary}{11cm}{L}
    \vspace{-2pt}\large{\bf{\textcolor{DarkBackground}{\textrm{LAN Switching Cheat Sheet}}}} \\
    \normalsize{by \textcolor{DarkBackground}{xavierjackson55} via \textcolor{DarkBackground}{\uline{cheatography.com/184445/cs/38481/}}}
\end{tabulary}
\end{multicols}}

\fancyfoot[L]{ \footnotesize
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{LL}
  \SetRowColor{FootBackground}
  \mymulticolumn{2}{p{5.377cm}}{\bf\textcolor{white}{Cheatographer}}  \\
  \vspace{-2pt}xavierjackson55 \\
  \uline{cheatography.com/xavierjackson55} \\
  \end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
  \SetRowColor{FootBackground}
  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Cheat Sheet}}  \\
   \vspace{-2pt}Not Yet Published.\\
   Updated 1st May, 2023.\\
   Page {\thepage} of \pageref{LastPage}.
\end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
  \SetRowColor{FootBackground}
  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Sponsor}}  \\
  \SetRowColor{white}
  \vspace{-5pt}
  %\includegraphics[width=48px,height=48px]{dave.jpeg}
  Measure your website readability!\\
  www.readability-score.com
\end{tabulary}
\end{multicols}}




\begin{document}
\raggedright
\raggedcolumns

% Set font size to small. Switch to any value
% from this page to resize cheat sheet text:
% www.emerson.emory.edu/services/latex/latex_169.html
\footnotesize % Small font.

\begin{multicols*}{2}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{What is a LAN?}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{A LAN stands for local area network. These are devices that are confined to a limited area. For example, a SOHO, or an office department etc. A LAN in its basic form can just be two computers plugged together. However, in most enterprise or office's, these LAN's are created by something called a switch. End-hosts are typically plugged into switches. These end hosts could be PC's or servers.% Row Count 8 (+ 8)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{What is a Switch?}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{A switch is a Layer 2 device. (Based on OSI Model) Switches typically have a lot of ports on them, unlike routers which typically do not have many interfaces on them. This makes switches great to plug into end hosts. \newline % Row Count 5 (+ 5)
The function of a switch is to forward traffic WITHIN LAN's. A router on the other hand will forward traffic BETWEEN LAN's.% Row Count 8 (+ 3)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Ethernet Switching}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{Ethernet Switching is when a switch forwards traffic to the correct end host within a LAN based upon MAC addresses. \newline % Row Count 3 (+ 3)
Ethernet itself is a Layer 2 protocol in the OSI Model, also known as the Data Link Layer. \newline % Row Count 5 (+ 2)
The PDU (Protocol Data Unit) at Layer 2 is known as a Frame. Thus Ethernet Frames are what are sent when sending traffic within LAN's.% Row Count 8 (+ 3)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Ethernet Frames}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{The Minimum size for an Ethernet Frame is 64 Bytes. 1 Byte = 8 Bits, so 64 Bytes = 512. \newline % Row Count 2 (+ 2)
An Ethernet Frame will include an Ethernet header, a packet (encapsulated from Layer 3) and a trailer. This would make the minimum size if everything included to 64 bytes. \newline % Row Count 6 (+ 4)
Minimum PAYLOAD size is 46. If \textless{}46 padding bytes are added to the frame to add upto 46. (Below explains why)% Row Count 9 (+ 3)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Ethernet Header: (Without 802.1Q)}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{8.4cm}}{The Ethernet Header is comprised of 4 main sections (There are optional ones, like VLAN 802.1q which isnt explained here).  These are Preamble \& SFD, Destination \& Source, Type, and CRC.} \tn 
% Row Count 4 (+ 4)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{{\bf{Preamble \& SFD:}} The preamble is 7 bytes long. (56 bits) Its main purpose is to allow devices to sync their reciever clocks.  The SFD is 1 byte long (8 bits) and is used to mark the end of the rest of the frame.  The preamble \& SFD are usually not considered part of the ethernet frame. So, without this, the ethernet payload is 64-18 (Preamble +SFD) = 46. So, if it is \textless{}46 padding is added.} \tn 
% Row Count 12 (+ 8)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{8.4cm}}{{\bf{Destination \& Source:}} These sections indicate the source \& destination of where the frame is headed too.  Inside these it includes MAC addresses, which are 6 bytes in length. So it will be 6 bytes for both the Destination \& the Source.  In ethernet frames destination comes before source, because of something called ARP.} \tn 
% Row Count 19 (+ 7)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{{\bf{Type/Length:}} 2 Bytes in Length. (16 Bits) A value of 1500 or less indicates the length of the encapsulated packet. A value of 1536 or higher indicates the TYPE of encapsulated packet. For example IPv4 = 2048, IPv6 = 34,525.} \tn 
% Row Count 24 (+ 5)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
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\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{MAC Addresses}}  \tn
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{MAC Address stands for Media Access control.  \newline % Row Count 1 (+ 1)
Its 6 bytes in Length. Its usually assigned/burnt into the device when it is manufactured. (Usually to the NIC).  \newline % Row Count 4 (+ 3)
The first 3 bytes are the OUI (Organizationally Unique Identifier, which is assigned to the company making the network device.  \newline % Row Count 7 (+ 3)
The Last 3 bytes are unique to the device itself.  \newline % Row Count 9 (+ 2)
It is also written is hexadecimal. (Not included here)% Row Count 11 (+ 2)
} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}


% That's all folks
\end{multicols*}

\end{document}