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Nico Schottelius 3 years ago
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      doc/Background.tex

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doc/Background.tex

@ -4,7 +4,7 @@ relation to our work.
% ----------------------------------------------------------------------
\section{\label{background:p4}P4}
P4 is a programming language designed to program inside network
equipment. It's main features are protocol and target independence.
equipment. Its main features are protocol and target independence.
The \textit{protocol independence} refers to the separation of concerns in
terms of language and protocols: P4, generally speaking, operates on
bits that are parsed and then accessible in the self defined
@ -23,7 +23,7 @@ parser will read and parse in the ingress pipeline one protocol
\end{figure}
The \textit{target independence} is the second very powerful feature
of P4: it allows code to be compiled to different targets. While in
theory the P4 code should be completely target independent, in reality
theory the P4 code should be completely target independent, in reality,
there are some modifications needed on a per-target basis and each
target faces different restrictions. The challenges arising from this
are discussed in section \ref{results:p4}.
@ -44,7 +44,7 @@ consider transmission via Ethernet, which operates at
layer 2. Inside the Ethernet frame a field named ``type'' specifies
the higher level protocol identifier.\footnote{
0x0800 for IPv4~\cite{rfc894} and 0x86DD for IPv6~\cite{rfc2464}.}
This is important, because
This is important because
Ethernet can only reference one protocol, which makes IPv4 and IPv6
mutually exclusive.
The figures \ref{fig:ipv4header} and \ref{fig:ipv6header} show the
@ -81,7 +81,7 @@ The major difference between ARP and NDP in relation to P4 are
\item ARP is a separate protocol on the same layer as IPv6 and IPv4,
\item NDP operates below ICMP6 which operates below IPv6,
\item NDP contains checksums over payload,
\item and NDP in ICMP6 contains optional, non referenced option fields
\item and NDP in ICMP6 contains optional, non-referenced option fields
(specifically: ICMP6 link layer address option).
\end{itemize}
ARP is required to be a separate protocol, because IPv4 hosts don't
@ -99,8 +99,7 @@ collision domain is significantly reduced in IPv6, compared to IPv4.
As seen later in this document (compare
section \ref{results:netpfga:features}), the requirement to generate checksums
over payload poses difficult problems for some hardware targets. Even
more difficult is the use of options within ICMP6. Figure shows a
typical layout of a neighbor advertisement messages.
more difficult is the use of options within ICMP6.
\begin{figure}[h]
\includegraphics[scale=0.3]{icmp6ndp}
\centering
@ -230,7 +229,7 @@ stateful NAT64, the translator needs to store the mapping in a table and
purge entries regularly.
Stateful NAT64 usually uses information found in protocols at layer 4
like TCP~\cite{rfc793} or UDP~\cite{rfc768}. However it can also
like TCP~\cite{rfc793} or UDP~\cite{rfc768}. However, it can also
support ICMP~\cite{rfc792} and ICMP6~\cite{rfc4443}.
% ----------------------------------------------------------------------
\subsection{\label{background:transition:Protocol dependent}Higher
@ -242,14 +241,14 @@ nginx~\cite{nginx:_nginx_high_perfor_load_balan}
use layer 7 protocol
information to proxy towards backends. Within this proxying method,
the underlying IP protocol can be changed from IPv6 to IPv4 and vice
versa. However the requested hostname that is usually used for
versa. However, the requested hostname that is usually used for
selecting the backend is encrypted in TLS 1.3~\cite{rfc8446}, which
poses a challenge for implementations.
While protocol dependent translation has the highest amount of
information to choose from for translation, complex parsers or even
cryptographic methods are required for it. That reduces the
opportunities of protocol dependent translation
opportunities of protocol dependent translation.
% ----------------------------------------------------------------------
\subsection{\label{background:transition:prefixnat}Mapping IPv4
Addresses in IPv6}
@ -260,8 +259,8 @@ practice to assign an IPv6 prefix for IPv6 hosts that represents a
mapping to the IPv4 Internet. In RFC6052~\cite{rfc6502} the well
known prefix \textit{64:ff9b::/96} is defined. One possibility to map
an IPv4 address into the prefix is by adding its integer value to the
prefix, treating it like an offset. In figure \ref{fig:ipv4embed}
we show an example python code of how this can be done.
prefix, treating it as an offset. In figure \ref{fig:ipv4embed}
we show example python code of how this can be done.
\begin{figure}[h]
\begin{verbatim}
>>> import ipaddress
@ -328,7 +327,7 @@ figure \ref{fig:dns64}.
\caption{Illustration of DNS64}
\label{fig:dns64}
\end{figure}
The DNS64 DNS server will query the authorative DNS server for an AAAA
The DNS64 DNS server will query the authoritative DNS server for an AAAA
record. However as the host \textit{ipv4onlyhost.example.com} is only
reachable by IPv4, it also only has an A entry. After receiving the
answer that there is no AAAA record, the DNS64 server will ask for an
@ -337,7 +336,7 @@ A record and gets an answer that the name
\textit{192.0.2.0}. The DNS64 server then embeds the IPv4 address in
the configured IPv6 prefix (\textit{64:ff9b::/96} in this case) and
returns a fake AAAA record to the IPv6 only host. The IPv6 only host
then will use address to connect to. The NAT64 translator recognises
then will use the address to connect to. The NAT64 translator recognises
either that the address is part of a configured prefix or that it has
a dedicated table entry for mapping this IPv6 address to an IPv4
address and translates it accordingly.
@ -380,7 +379,7 @@ defined in RFC768 and RFC793 and are shown in \ref{fig:ipv4pseudoheader}.
When translating, the checksum fields in the higher protocols need to be
adjusted. The checksums for TCP and UDP is calculated not only over the pseudo
headers, but also contain the payload of the packet. This is
important, because some targets (like the NetFPGA) do not allow to
important because some targets (like the NetFPGA) do not allow to
access the payload (see section \ref{design:netpfga}).
\begin{figure}[h]
\begin{verbatim}
@ -447,7 +446,7 @@ systems is not an easy task~\cite{ungleich:_ipv4}.
%% \end{figure}
While the three network designs look similar, there are significant
differences in operating them and limitations that are not easy to
circumvent. In the following sections we describe the limitations and
circumvent. In the following sections, we describe the limitations and
reason how a translation mechanism like our NAT64 implementation
should be deployed.
% ----------------------------------------------------------------------
@ -473,7 +472,7 @@ tables double, the firewall rules roughly double\footnote{The rule sets
even for identical policies in IPv6 and IPv4 networks are not
identical, but similar. For this reason we state that roughly double
the amount of firewall rules are required for the same policy to be
applied.} and the number of network supporting systems (like DHCPv4,
applied.} and the number of network supporting systems, (like DHCPv4,
DHCPv6, router advertisement daemons, etc.) also roughly double.
Additionally services that run on either IPv6 or IPv4 might need to be
configured to run in dualstack mode as well and not every software

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