I do know that vertical separators in the tables are not best practice, but in some rare cases I need them.
As you can see from the code bellow the separator between cells 'Switch fcsw1' and 'Switch fcsw1' is missed. How could it be?
\documentclass[a4paper,10pt]{article}
\usepackage{ucs}
\usepackage[utf8]{inputenc}
\usepackage[ukrainian]{babel}
\usepackage[T1,T2A]{fontenc}
\usepackage{multirow, booktabs, array, adjustbox}
\renewcommand{\arraystretch}{1.3}
\begin{document}
\section{Multicolumn and multorow table}
\begin{table}[h]
\centering
\begin{adjustbox}{width=1\textwidth}
\begin{tabular}{l|l|l|l|l} \toprule
\multirow{3}{*}{\textbf{Device}} & \multicolumn{4}{l}{\textbf{Alias}} \\ \cline{2-5}
& \multicolumn{2}{l}{\textbf{Switch fcsw1}} & \multicolumn{2}{l}{\textbf{Switch fcsw2}} \\ \cline{2-5}
& \textbf{name} & \textbf{WWN} & \textbf{name} & \textbf{WWN} \\ \midrule
\multirow{2}{*}{Big Device 1} & DevA01\textunderscore A & 50:00:00:00:00:00:00:00 & aDevA01\textunderscore A & 50:00:00:00:00:00:00:00 \\
& DevA01\textunderscore B & 50:00:00:00:00:00:00:00 & aDevA01\textunderscore B & 50:00:00:00:00:00:00:00 \\ \midrule
\multirow{2}{*}{Big Device 2} & DevA02\textunderscore A & 50:00:00:00:00:00:00:00 & aDevA02\textunderscore A & 50:00:00:00:00:00:00:00 \\
& DevA02\textunderscore B & 50:00:00:00:00:00:00:00 & aDevA02\textunderscore B & 50:00:00:00:00:00:00:00 \\ \midrule
Small Device 3 & 50:00:00:00:00:00:00:00 & aKYVDC01BAK26 & 50:00:00:00:00:00:00:00 \\
Small Device 4 & aDevX01 & 50:00:00:00:00:00:00:00 & aDevX01 & 50:00:00:00:00:00:00:00 \\
Small Device 5 & aDevX02 & 50:00:00:00:00:00:00:00 & aDevX02 & 50:00:00:00:00:00:00:00 \\ \bottomrule
\end{tabular}
\end{adjustbox}
\caption{MRMC Table}
\label{table:1}
\end{table}
\end{document}
booktabs
such as\toprule
and\midrule
, which are designed not to work with vertical rules. – egreg Apr 10 '18 at 17:39