diff --git a/doc/Background.tex b/doc/Background.tex index 570acb2..fcce639 100644 --- a/doc/Background.tex +++ b/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