\documentclass[10pt,a4paper]{article}

% Packages
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\usepackage{multicol}           % Allows multicols in tables
\usepackage{tabularx}           % Intelligent column widths
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\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{bytebar}
\pdfinfo{
  /Title (osi-model.pdf)
  /Creator (Cheatography)
  /Author (bytebar)
  /Subject (OSI Model Cheat Sheet)
}

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% This two commands together give roughly
% the right line height in the tables
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% Commands
\newcommand{\SetRowColor}[1]{\noalign{\gdef\RowColorName{#1}}\rowcolor{\RowColorName}} % Shortcut for row colour
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% 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{OSI Model Cheat Sheet}}}} \\
    \normalsize{by \textcolor{DarkBackground}{bytebar} via \textcolor{DarkBackground}{\uline{cheatography.com/218949/cs/48436/}}}
\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}bytebar \\
  \uline{cheatography.com/bytebar} \\
  \end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
  \SetRowColor{FootBackground}
  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Cheat Sheet}}  \\
   \vspace{-2pt}Published 14th September, 2026.\\
   Updated 14th September, 2026.\\
   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{tabularx}{17.67cm}{x{6.0445 cm} x{11.2255 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{17.67cm}}{\bf\textcolor{white}{The 7 Layers}}  \tn
% Row 0
\SetRowColor{LightBackground}
{\bf{7 — Application}} & User-facing services. Protocols: HTTP, FTP, SMTP, DNS, DHCP \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
{\bf{6 — Presentation}} & Data format, encryption, compression. Protocols: TLS/SSL, JPEG, ASCII \tn 
% Row Count 6 (+ 3)
% Row 2
\SetRowColor{LightBackground}
{\bf{5 — Session}} & Connections between apps. Protocols: NetBIOS, RPC, PPTP \tn 
% Row Count 9 (+ 3)
% Row 3
\SetRowColor{white}
{\bf{4 — Transport}} & End-to-end delivery, ports. Protocols: {\bf{TCP, UDP}}. Devices: Firewall (stateful) \tn 
% Row Count 13 (+ 4)
% Row 4
\SetRowColor{LightBackground}
{\bf{3 — Network}} & Routing, logical addressing. Protocols: {\bf{IP, ICMP}}, OSPF, BGP. Devices: {\bf{Router}}, L3 switch \tn 
% Row Count 17 (+ 4)
% Row 5
\SetRowColor{white}
{\bf{2 — Data Link}} & Switch-to-switch, MAC addressing. Protocols: Ethernet, ARP, PPP. Devices: {\bf{Switch}}, bridge, NIC \tn 
% Row Count 21 (+ 4)
% Row 6
\SetRowColor{LightBackground}
{\bf{1 — Physical}} & Bits on the wire. Devices: Hub, repeater, cables \tn 
% Row Count 23 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{17.67cm}}{All 7 layers, what lives at each, and the mnemonics that make them stick.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{17.67cm}{x{5.3537 cm} x{11.9163 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{17.67cm}}{\bf\textcolor{white}{Mnemonics}}  \tn
% Row 0
\SetRowColor{LightBackground}
{\bf{Top → bottom}} & {\emph{All People Seem To Need Data Processing}} \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
{\bf{Bottom → top}} & {\emph{Please Do Not Throw Sausage Pizza Away}} \tn 
% Row Count 4 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{17.67cm}}{Say them out loud until they stick.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{17.67cm}{x{5.3537 cm} x{11.9163 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{17.67cm}}{\bf\textcolor{white}{Data Names per Layer}}  \tn
% Row 0
\SetRowColor{LightBackground}
{\bf{4 Transport}} & {\bf{Segment}} (TCP) / Datagram (UDP) \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
{\bf{3 Network}} & {\bf{Packet}} \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
{\bf{2 Data Link}} & {\bf{Frame}} \tn 
% Row Count 6 (+ 2)
% Row 3
\SetRowColor{white}
{\bf{1 Physical}} & {\bf{Bits}} \tn 
% Row Count 8 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{17.67cm}}{Exam trick: What PDU at Layer 3? → {\bf{Packet}}. Layer 2 → {\bf{Frame}}. Layer 4 → {\bf{Segment}}.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{17.67cm}{x{5.3537 cm} x{11.9163 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{17.67cm}}{\bf\textcolor{white}{TCP/IP Model vs OSI}}  \tn
% Row 0
\SetRowColor{LightBackground}
{\bf{Application}} & 7 + 6 + 5 (Application, Presentation, Session) \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
{\bf{Transport}} & 4 (Transport) \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
{\bf{Internet}} & 3 (Network) \tn 
% Row Count 5 (+ 1)
% Row 3
\SetRowColor{white}
{\bf{Network Access}} & 2 + 1 (Data Link, Physical) \tn 
% Row Count 7 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{17.67cm}}{The 4-layer model collapses OSI's top three and bottom two.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{17.67cm}{x{6.3899 cm} x{10.8801 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{17.67cm}}{\bf\textcolor{white}{Quick Exam Hits}}  \tn
% Row 0
\SetRowColor{LightBackground}
{\bf{ARP}} & Works at Layer 2/3 boundary (resolves IP → MAC) \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
{\bf{TLS}} & Lives at Layer 6 (Presentation) \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
{\bf{Switches vs Routers}} & Switches = Layer 2 (MAC addresses) · Routers = Layer 3 (IP addresses) \tn 
% Row Count 7 (+ 3)
% Row 3
\SetRowColor{white}
{\bf{MTU}} & MTU issues and fragmentation → Layer 3 \tn 
% Row Count 9 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{17.67cm}}{If you remember nothing else, remember these four.}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}



\end{document}