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+\documentclass[a4paper,12pt]{article}
+\usepackage[english,vietnamese]{babel}
+\usepackage{booktabs}
+\usepackage{lmodern}
+\usepackage{hyperref}
+\usepackage{siunitx}
+\usepackage[nottoc,numbib]{tocbibind}
+\renewcommand{\thefootnote}{\fnsymbol{footnote}}
+\newcommand{\byte}{\mathrm{B}}
+
+\title{Teredo Tunnel Simulation}
+\author{\selectlanguage{vietnamese}Nguyễn Gia Phong---BI9-184}
+
+\begin{document}
+\selectlanguage{english}
+\maketitle
+\tableofcontents
+
+\newpage
+\section{Introduction}
+\subsection{Brief Description}
+Internet Protocol version 6 (IPv6), the most recent version of
+the Internet Protocol, was developed by the IETF to deal with
+the long-anticipated problem of IPv4 address exhaustion.  Despite being
+superior to IPv4 in multiple aspect (e.g. larger address space,
+extension headers), IPv6 has not been widely adopted, although it has been
+semi-standardized in 1998 and fully-standardized in 2017~\cite{rfc8200}.
+
+During the transition period, teredo tunneling has been used to give
+IPv6 connectivity for IPv6-capable hosts that are on the IPv4 Internet
+but have no native connection to an IPv6 network~\cite{rfc4380}.
+In this article, I will demontrate a way to set up such tunnel up
+on virtual machines, then examine the packets being sent by IPv6 nodes
+connected by the tunnel.
+
+\subsection{Licensing and Attribution}
+This work is licensed under a CC BY-SA 4.0 license.
+
+Aside from the listed references, I would also like to express my gratitude
+toward Dr. {\selectlanguage{vietnamese}Giang Anh Tuấn}, whose teaching material
+gave me basic understanding on computer network as well as a chance to practice
+on networking studies like this.\footnote{I would never have the motivation to
+self-study this subject otherwise.}  In addition, I want to thank user
+\textbf{detonate} in Freenode's \#ipv6, who pointed out to me that local
+IPv6 addresses (\verb|fe80::/64|) are not forwardable.
+
+\section{Configuration}
+\subsection{Virtual Machines}
+In order to simulate Teredo tunneling, one needs two IPv6 nodes and two routers
+with both IPv4 and IPv6 access.  In total, there needs to be four
+virtual machines to be set up, thus I went for Void Linux, which is known
+for its low memory foot print thanks to using \verb|runit| instead
+of \verb|systemd|.  To minimize resource usage and speed up the setup process,
+I chose the barebone live image which uses \verb|musl| instead of \verb|glibc|.
+At boot, the image uses only \SI{40}{\mega\byte} of memory.
+
+For virtualization, I use \verb|vert-manager|, simply because it is available
+in Debian's repository (my host OS).  For some reason, on \verb|amd64|,
+the kernel refuses to boot until I give it over \SI{200}{\mega\byte},
+but apparently that is still a really modest number.  Networking is provided
+to the guest OSes via NAT with default configurations.
+
+It is worth mentioning that through \verb|virtio|, one may use SSH to log into
+the guests systems from the host OS.  I find this especially convenient as
+it enables me to copy and paste not only commands but also IP addresses between
+host and guests as well as between guests.
+
+For convenience, from now on, the outside nodes will be referred to as PC~A and
+PC~B, on the other hand the routers are named Router~A and Router~B.  Upon boot,
+they were given an Ethernet interface \verb|eth0| with the following addresses
+\begin{center}
+  \begin{tabular}{c c c}
+    \toprule
+    Node & MAC & IPv4\\
+    \midrule
+    Router A & \verb|52:54:00:f0:85:c7| & \verb|192.168.122.127|\\
+    Router B & \verb|52:54:00:2b:01:cc| & \verb|192.168.122.134|\\
+    PC A & \verb|52:54:00:3b:82:36| & \verb|192.168.122.86|\,\,\,\\
+    PC B & \verb|52:54:00:7b:ed:c0| & \verb|192.168.122.255|\\
+    \bottomrule
+  \end{tabular}
+\end{center}
+
+Local IPv6 addresses were also given but we are not going to need them.
+
+\subsection{Teredo Tunnel Setup}
+First, I set up a IPv4 tunnel between the two routers:
+\begin{verbatim}
+# On Router A
+ip tunnel add tunn mode sit remote 192.168.122.134 ttl 255
+ip link set tunn up
+# On Router B
+ip tunnel add tunn mode sit remote 192.168.122.127 ttl 255
+ip link set tunn up
+\end{verbatim}
+
+For this tunnel to be able to act as a Teredo one, the two routers needs
+to have IPv6 addresses prefixed by \verb|2001::/32|~\cite{rfc4380}:
+\begin{verbatim}
+# On Router A
+ip -6 addr add 2001:2::1/64 dev eth0
+# On Router B
+ip -6 addr add 2001:3::1/64 dev eth0
+\end{verbatim}
+
+Finally, I fellback all IPv6 lookups to the tunnel and enabled IPv6 forwarding:
+\begin{verbatim}
+ip -6 route add default dev tunn
+sysctl -w net.ipv6.conf.all.forwarding=1
+\end{verbatim}
+
+\subsection{Teredo Tunnel Usage}
+The IPv6 addresses of the PCs were set up as follows
+(\verb|0x8067| is \verb|PC| in ASCII)
+\begin{verbatim}
+# On PC A
+ip -6 address add 2001:2::8067/64 dev eth0
+# On PC B
+ip -6 address add 2001:3::8067/64 dev eth0
+\end{verbatim}
+
+By giving both Router~A and PC~A addresses prefixed by \verb|2001:2::/64|
+(similarly for Router~B and PC~B), I implied that they can find each other
+through the local IPv6 network, for example on PC~B
+\begin{verbatim}
+$ ip -6 route | head -n1
+2001:3::/64 dev eth0 proto kernel metric 256 pref medium
+\end{verbatim}
+
+To use the newly created tunnel,
+the PCs simple had to be routed directly to the routers
+\begin{verbatim}
+# On PC A
+ip -6 route add default via 2001:2::1
+# On PC B
+ip -6 route add default via 2001:3::1
+\end{verbatim}
+
+The connection could then be verified by running on PC~A
+\begin{verbatim}
+$ traceroute 2001:3::8067
+traceroute to 2001:3::8067 (2001:3::8067), 30 hops max, 80 byte packets
+ 1  2001:2::1 (2001:2::1)  0.572 ms  0.441 ms  0.328 ms
+ 2  2001:3::1 (2001:3::1)  0.906 ms  0.888 ms  1.049 ms
+ 3  2001:3::8067 (2001:3::8067)  1.325 ms  1.174 ms  1.091 ms
+\end{verbatim}
+
+\section{Analysis}
+To gain further understanding on how packets are transferred over
+the Teredo tunnel, I captured and took a closer look at some of them.
+
+\subsection{Packets Capturing}
+Fortunately for me\footnote{Aside from web browsing, I also run an IPFS node
+and a bunch of local servers.  I probably need to retire some of them soon
+since they really clutter the traffic.}, all traffic of guests OSes were wired
+to an separate interface named \verb|virbr0|.  To capture going through
+the tunnel, I simply had to tell Wireshark to listen to the interface,
+while letting PC~A ping PC~B though IPv6: \verb|ping -c1 2001:3::8067|.
+I then skimmed through the packets sent between the two nodes and looked for
+the IPv6-in-IPv4 ones.
+
+\subsection{Packet Contents}
+Catured IPv6-in-IPv4 looks exactly like how I would imagined it to be.
+The content of the ping request can be partially decoded as follows.
+
+\subsubsection{Ethernet Header}
+\paragraph{52 54 00 2b 01 cc} MAC address of Router B (destination)
+\paragraph{52 54 00 f0 85 c7} MAC address of Router A (source)
+\paragraph{08 00} EtherType of IPv4
+
+\subsubsection{IPv4 Header}
+\paragraph{45 00 00 7c 9b 43 40 00 ff} Some flags
+\paragraph{29} Protocol of \emph{IPv6}
+\paragraph{69 be} Checksum
+\paragraph{c0 a8 7a 86} IPv4 address of Router B (destination)
+\paragraph{c0 a8 7a 7f} IPv4 address of Router A (source)
+
+\subsubsection{IPv6 Header}
+\paragraph{60 00 07 e7 00 40} Some flags
+\paragraph{3a} Next header (ICMPv6)
+\paragraph{3f} Hop limit of 63
+\paragraph{20 01 00 02 00 00 00 00 00 00 00 00 00 00 80 67} PC~A's IPv6 address
+\paragraph{20 01 00 03 00 00 00 00 00 00 00 00 00 00 80 67} PC~B's IPv6 address
+
+\subsubsection{ICMPv6}
+\paragraph{80} Type of ping request
+\paragraph{00 cf be 03 d9 00 01} Some flags
+\paragraph{e3 0d fe 5e 00 00 00 00 bc d6 0e 00 00 00
+00 00 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d
+1e 1f 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d
+2e 2f 30 31 32 33 34 35 36 37} Binary data to be echoed
+
+\section{Conclusion}
+Via the activities elaborated above, the procedure to set up a Teredo tunnel
+and the content of the packets travelling through it could be well understood.
+These understanding may help facilite the adoption of IPv6, even for IPv6 nodes
+having no native connection to an IPv6 network.  I hope that the IPv6 will grow
+fast enough that I can see the day measures like this tunnel can soon
+be deprecated.
+
+\begin{thebibliography}{99}
+  \bibitem{rfc8200} C.~Huitema.
+    \emph{Teredo: Tunneling IPv6 over UDP
+          through Network Address Translations (NATs)}.
+    Internet Engineering Task Force, February 2006.
+    \href{https://tools.ietf.org/html/rfc4380}{RFC 4380}.
+  \bibitem{rfc4380} S.~Deering, R.~Hinden.
+    \emph{Internet Protocol, Version 6 (IPv6) Specification}.
+    Internet Engineering Task Force, July 2017.
+    \href{https://tools.ietf.org/html/rfc8200}{RFC 8200}.
+\end{thebibliography}
+\end{document}