master-thesis/doc/Results.tex

\chapter{\label{results}Results}
%** Results.tex: What were the results achieved including an evaluation
%
This section describes the achieved results and compares the P4 based
implementation with real world software solutions.

We distinguish the software implementation of P4 (BMV2) and the
hardware implementation (NetFPGA) due to significant differences in
deployment and development. We present benchmarks for the existing
software solutions as well as for our hardware implementation. As the
objective of this thesis was to demonstrate the high speed
capabilities of NAT64 in hardware, no benchmarks were performed on the
P4 software implementation.
% ok
% ----------------------------------------------------------------------
\section{\label{results:p4}P4 based implementations}
All planned features could be realised with P4 and a controller.
For this thesis the parsing capabilities of P4 were adequate.
However P4, at the time of writing, cannot parse ICMP6 options in
general, as the upper level protocol does not specify the number
of options that follow and parsing of an undefined number
of 64 bit blocks is required.

The language has some limitations on where the placement of
conditional statements (\texttt{if/switch}).\footnote{In general,
if and switch statements in actions lead to errors,
but not all constellations are forbidden.}
Furthermore P4/BMV2 does not support for multiple LPM keys in a table,
however it supports multiple keys with ternary matching, which is a
superset of LPM matching.

When developing P4 programs, the reason for incorrect behaviour we
have seen were checksum problems. This is in retrospective expected,
as the main task our implementation does is modify headers on which
the checksums depend. In all cases we have seen Ethernet frame
checksum errors, the effective length of the packet was incorrect.

The tooling around P4 is somewhat fragile. We encountered small
language bugs during the development~\cite{schottelius:github1675},
\ref{appendix:expressionbug}
or found missing features~\cite{schottelius:github745},
~\cite{theojepsen:_get}: it is at the moment impossible to retrieve
the matching key from table or the name of the action called. Thus
if different table entries call the same action, it is impossible
within the action, or if forwarded to the controller, within the
controller to distinguish on which match the action was
triggered. This problem is very consistent within P4, as not even the
matching table name can be retrieved. While these information can be
added manually as additional fields in the table entries, we would
expect a language to support reading and forwarding this kind of meta
information.

While in P4 the P4 code and the related controller are tightly
coupled, their data definitions are not. Thus the packet format
definition that is used between the P4 switch and the controller has
to be duplicated. Our experiences in software development indicate
that this duplication is a likely source of errors in bigger software
projects.

The supporting scripts in the P4 toolchain are usually written in
python2. However python2 ``is
legacy''~\cite{various:_shoul_i_python_python}. During development
errors with unicode string handling in python2 caused
changes to IPv6 addresses.~\ref{appendix:p4:python2unicode}

P4os - reusable code

% idomatic problem: Security issue: not checking checksums before


****** TODO IPv6 udp -> IPv4
- Got 4-5 tuple ([proto], src ip, src port, dst ip, dst port)
- Does not / never signal end
- Needs timeout for cleaning up

 P4/BMV2 thus
allows us to closest resemble any other translation implementation.

Only supporting /96, not other embeddings as described in
section \ref{background:transition:prefixnat}.

% ----------------------------------------------------------------------
\subsection{\label{Results:BMV2}BMV2}
The software implementation of P4 has most features, which is
mostly due to the capability of checksumming the payload: Acting
as a ``proper'' participant in NDP, requires the host to calculate
checksums over the payload.


List of features BMV2 ~\cite{tab:p4bmv2features}

\begin{table}[htbp]
\begin{center}\begin{minipage}{\textwidth}
\begin{tabular}{| c | c | c |}
\hline
\textbf{Feature} & \textbf{Description} & \textbf{Status} \\
\hline
Switch to controller & Switch forwards unhandeled packets to
controller & fully implemented\footnote{Source code: \texttt{actions\_egress.p4}}\\
\hline
Controller to Switch & Controller can setup table entries &
fully implemented\footnote{Source code: \texttt{controller.py}}\\
\hline
NDP & Switch responds to ICMP6 neighbor  & \\
    & solicitation request (without controller) &
fully implemented\footnote{Source code:
  \texttt{actions\_icmp6\_ndp\_icmp.p4}} \\
\hline
ARP & Switch can answer ARP request (without controller) & fully
implemented\footnote{Source code: \texttt{actions\_arp.p4}}\\
\hline
ICMP6 & Switch responds to ICMP6 echo request (without controller) &
fully implemented\footnote{Source code: \texttt{actions\_icmp6\_ndp\_icmp.p4}} \\
\hline
ICMP & Switch responds to ICMP echo request (without controller) &
fully implemented\footnote{Source code: \texttt{actions\_icmp6\_ndp\_icmp.p4}} \\
\hline
NAT64: TCP & Switch translates TCP with checksumming & \\
& from/to IPv6 to/from IPv4 &
fully implemented\footnote{Source code: \texttt{actions\_nat64\_generic\_icmp.p4}} \\
\hline
NAT64: UDP & Switch translates UDP with checksumming & \\
& from/to IPv6 to/from IPv4 &
fully implemented\footnote{Source code: \texttt{actions\_nat64\_generic\_icmp.p4}} \\
\hline
NAT64:  & Switch translates echo request/reply & \\
ICMP/ICMP6 & from/to ICMP6 to/from ICMP with checksumming &
fully implemented\footnote{Source code: \texttt{actions\_nat64\_generic\_icmp.p4}} \\
\hline
NAT64: Sessions  & Switch and controller create 1:n sessions/mappings &
fully implemented\footnote{Source code:
  \texttt{actions\_nat64\_session.p4}, \texttt{controller.py}} \\
\hline
Delta Checksum & Switch can calculate checksum without payload
inspection &
fully implemented\footnote{Source code: \texttt{actions\_delta\_checksum.p4}}\\
\hline
Payload Checksum & Switch can calculate checksum with payload inspection &
fully implemented\footnote{Source code: \texttt{checksum\_bmv2.p4}}\\
\hline
\end{tabular}
\end{minipage}
\caption{P4 / BMV2 feature list}
\label{tab:p4bmv2features}
\end{center}
\end{table}

Responds to icmp, icmp6
ndp ~\cite{rfc4861}
arp

very easy to use

Fully functional host
Can compute checksums on its own.

focus on typical use cases of icmp, icmp6, the software implementation
supports translating echo request and echo reply messages, but does
not support all ICMP/ICMP6 translations that are defined in
RFC6145~\cite{rfc6145}.

Stateful : no automatic removal

Session management not benchmarked, as it is only a matter of creating
table entries.

Jool and tayga are supported by


% ----------------------------------------------------------------------
\subsection{\label{results:netpfga}NetFPGA - FIXME: writing}
The reduced feature set of the NetPFGA implementation is due to two
factors: compile time. Between 2 to 6 hours per compile run. No
payload checksum

overview - general translation - not advanced features
% ----------------------------------------------------------------------
\subsubsection{\label{results:netpfga:features}Features}
\begin{table}[htbp]
\begin{center}\begin{minipage}{\textwidth}
\begin{tabular}{| c | c | c |}
\hline
\textbf{Feature} & \textbf{Description} & \textbf{Status} \\
\hline
Switch to controller & Switch forwards unhandeled packets to
controller & portable\footnote{While the NetFPGA P4 implementation
  does not have the clone3() extern that the BMV2 implementation offers,
communication to the controller can easily be realised by using one of
the additional ports of the NetFPGA and connect a physical network
card to it.}\\
\hline
Controller to Switch & Controller can setup table entries &
portable\footnote{The p4utils suite offers an easy access to the
  switch tables. While the P4-NetFPGA support repository also offers
  python scripts to modify the switch tables, the code is less
  sophisticated and more fragile.}\\
\hline
NDP & Switch responds to ICMP6 neighbor  & \\
    & solicitation request (without controller) &
portable\footnote{NetFPGA/P4 does not offer calculating the checksume
  over the payload. However delta checksumming can be used to create
  the required checksum for replying.} \\
\hline
ARP & Switch can answer ARP request (without controller) &
portable\footnote{As ARP does not use checksums, integrating the
  source code \texttt{actions\_arp.p4} into the netpfga code base is
  enough to enable ARP support in the NetPFGA.} \\
\hline
ICMP6 & Switch responds to ICMP6 echo request (without controller) &
portable\footnote{Same reasoning as NDP.} \\
\hline
ICMP & Switch responds to ICMP echo request (without controller) &
portable\footnote{Same reasoning as NDP.} \\
\hline
NAT64: TCP & Switch translates TCP with checksumming & \\
& from/to IPv6 to/from IPv4 &
fully implemented\footnote{Source code: \texttt{actions\_nat64\_generic\_icmp.p4}} \\
\hline
NAT64: UDP & Switch translates UDP with checksumming & \\
& from/to IPv6 to/from IPv4 &
fully implemented\footnote{Source code: \texttt{actions\_nat64\_generic\_icmp.p4}} \\
\hline
NAT64:  & Switch translates echo request/reply & \\
ICMP/ICMP6 & from/to ICMP6 to/from ICMP with checksumming &
portable\footnote{ICMP/ICMP6 translations only require enabling the
  icmp/icmp6 code in the netpfga code base.} \\
\hline
NAT64: Sessions & Switch and controller create 1:n sessions/mappings &
portable\footnote{Same reasoning as ``Controller to switch''.} \\
\hline
Delta Checksum & Switch can calculate checksum without payload
inspection &
fully implemented\footnote{Source code: \texttt{actions\_delta\_checksum.p4}}\\
\hline
Payload Checksum & Switch can calculate checksum with payload inspection &
unsupported\footnote{To support creating payload checksums, either an
  HDL module needs to be created or to modify the generated
  the PX program.~\cite{schottelius:_exter_p4_netpf}} \\
\hline
\end{tabular}
\end{minipage}
\caption{P4 / NetFPGA feature list}
\label{tab:p4netpfgafeatures}
\end{center}
\end{table}
% ----------------------------------------------------------------------
\subsubsection{\label{results:netpfga:stability}Stability}
Two different NetPFGA cards were used during the development of the
thesis. The first card had consistent ioctl errors (compare section
\ref{netpfgaioctlerror}) when writing table entries. The available
hardware tests (compare figures \ref{fig:hwtestnico} and
\ref{fig:hwtesthendrik}) showed failures in both cards, however the
first card reported an additional ``10G\_Loopback'' failure. Due to
the inability of setting table entries, no benchmarking was performed
on the first NetFPGA card.
\begin{figure}[h]
  \includegraphics[scale=1.4]{hwtestnico}
  \centering
  \caption{Hardware Test NetPFGA card 1}
  \label{fig:hwtestnico}
\end{figure}
\begin{figure}[h]
  \includegraphics[scale=0.2]{hwtesthendrik}
  \centering
  \caption{Hardware Test NetPFGA card 2, ~\cite{hendrik:_p4_progr_fpga_semes_thesis_sa}}
  \label{fig:hwtesthendrik}
\end{figure}
During the development and benchmarking, the second NetFPGA card stopped to
function properly multiple times. In both cases the card would not
forward packets anymore. Multiple reboots (3 were usually enough)
and multiple times reflashing the bitstream to the NetFPGA usually
restored the intended behaviour. However due to this ``crashes'', it
was impossible to complete a full benchmark run that would last for
more than one hour.

Sometimes it was also required to reboot the host containing the
NetFPGA card 3 times to enable successful flashing.\footnote{Typical
output of the flashing process would be: ``fpga configuration failed. DONE PIN is not HIGH''}
% ----------------------------------------------------------------------
\subsubsection{\label{results:netpfga:performance}Performance}
As expected, the NetFGPA card performed at near line speed and offers
NAT64 translations at 9.28 Gbit/s. Single and multiple streams
performed almost exactly identical and have been consistent through
multiple iterations of the benchmarks.
% ----------------------------------------------------------------------
\subsubsection{\label{results:netpfga:usability}Usability}
To use the NetFGPA, Vivado and SDNET provided by Xilinx need to be
installed. However a bug in the installer triggers an infinite loop,
if a certain shared library\footnote{The required shared library
is libncurses5.} is missing on the target operating system. The
installation program seems still to be progressing, however does never
finish.

While the NetFPGA card supports P4, the toolchains and supporting
scripts are in a immature state. The compilation process consists of
at least 9 different steps, which are interdependent\footnote{See
source code \texttt{bin/do-all-steps.sh}.} Some of the steps generate
shell scripts and python scripts that in turn generate JSON
data.\footnote{One compilation step calls the script
``config\_writes.py''. This script failed with a syntax error, as it
contained incomplete python code. The scripts config\_writes.py
and config\_writes.sh are generated by gen\_config\_writes.py.
The output of the script gen\_config\_writes.py depends on the content
of config\_writes.txt. That file is generated by the simulation
``xsim''. The file ``SimpleSumeSwitch\_tb.sv'' contains code that is
responsible for writing config\_writes.txt and uses a function
named axi4\_lite\_master\_write\_request\_control for generating the
output. This in turn is dependent on the output of a script named
gen\_testdata.py.}

However incorrect parsing generates syntactically incorrect
scripts or scripts that generate incorrect output. The toolchain
provided by the NetFGPA-P4 repository contains more than 80000 lines
of code. The supporting scripts for setting table entries require
setting the parameters for all possible actions, not only for the
selected action. Supplying only the required parameters results in a
crash of the supporting script.

The documentation for using the NetFPGA-P4 repository is very
distributed and does not contain a reference on how to use the
tools. Mapping of egress ports and their metadata field are found in a
python script that is used for generating test data.

The compile process can take up to 6 hours and because the different
steps are interdependent, errors in a previous stage were in our
experiences detected hours after they happened. The resulting log
files of the compilation process can be up to 5 MB in size. Within
this log file various commands output references to other logfiles,
however the referenced logfiles do not exist before or after the
compile process.

During the compile process various informational, warning and error
messages are printed. However some informational messages constitute
critical errors, while on the other hand critical errors and syntax
errors often do not constitue a critical
error.\footnote{F.i. ``CRITICAL WARNING: [BD 41-737] Cannot set the
parameter TRANSLATION\_MODE on /axi\_interconnect\_0. It is
read-only.'' is a non critical warning.}
Also contradicting
output is generated.\footnote{While using version 2018.2, the following
message was printed: ``WARNING: command 'get\_user\_parameter' will be removed in the 2015.3
release, use 'get\_user\_parameters' instead''.}

Programs or scripts that are called during the compile process do not
necessarily exit non zero if they encountered a critical error. Thus
finding the source of an error can be difficult due to the compile
process continuing after critical errors occured. Not only programs
that have critical errors exit ``successfully'', but also python
scripts that encounter critical paths don't abort with raise(), but
print an error message to stdout and don't abort with an error.

The most often encountered critical compile error is
``Run 'impl\_1' has not been launched. Unable to open''. This error
indicates that something in the previous compile steps failed and can
refer to incorrectly generated testdata to unsupported LPM tables.

The NetFPGA kernel module provides access to virtual Linux
devices (nf0...nf3). However tcpdump does not see any packets that are
emitted from the switch. The only possibility to capture packets
that are emitted from the switch is by connecting a physical cable to
the port and capturing on the other side.

Jumbo frames\footnote{Frames with an MTU greater than 1500 bytes.} are
commonly used in 10 Gbit/s networks. According to
\ref{wikipedia:_jumbo}, even many gigabit network interface card
support jumbo frames. However according to emails on the private
NetPFGA mailing list, the NetFPGA only supports 1500 byte frames at
the moment and additional work is required to implement support for
bigger frames.

Our P4 source code required contains Xilinx
annotations\footnote{F.i. ``@Xilinx\_MaxPacketRegion(1024)''} that define
the maximum packet size in bits. We observed two different errors on
the output packet, if the incoming packets exceeds the specified size:
\begin{itemize}
\item The output packet is longer then the original packet.
\item The output packet is corrupted.
\end{itemize}

While most of the P4 language is supported on the netpfga, some key
techniques are missing or not supported.
\begin{itemize}
\item Analysing / accessing payload is not supported
\item Checksum computation over payload is not supported
\item Using LPM tables can lead to compilation errors
\item Depening on the match type, only certain table sizes are allowed
\end{itemize}
Renaming variables in the declaration of the parser or deparser lead
to compilation errors. Function syntax is not supported. For this
reason our implementation uses \texttt{\#define} statements instead of functions.

FIXME:

General result: limited NAT64 is working, however
  No Payload ;  checksumming - requires controller
Hash funktion in Arbeit  ;   No NDP, no ARP - focused on key factors of NAT64 translation,
other features can be supported by controller
Needed to debug internal parsing errors
debugging generated tcl code to debug impl1 error

% ----------------------------------------------------------------------
\section{\label{results:softwarenat64}Software based NAT64}
with Tayga and
  Jool
Both cpu bound.

During the benchmark cpu bound, single thread
tayga: Single threaded
easy to use

Jool kernel module
100\% cpu usage on 1 core for udp
0\% visible cpu usage for tcp, might be tcp offloading
Integration with iptables
Requires routing


% ----------------------------------------------------------------------
\section{\label{results:benchmark}NAT64 Benchmarks - FIXME: explain
  numbers}
% ----------------------------------------------------------------------
\subsection{\label{results:benchmark:design}Benchmark Design}
\begin{figure}[h]
  \includegraphics[scale=0.5]{softwarenat64design}
  \centering
  \caption{Benchmark design for NAT64 in software implementations}
  \label{fig:softwarenat64design}
\end{figure}
We use two hosts for performing benchmarks: a load generator and a
NAT64 translator. Both hosts are equipped with a dual port
Intel X520 10 Gbit/s network card. Both hosts are connected using DAC
without any equipment in between. TCP offloading is enabled in the
X520 cards. Figure \ref{fig:softwarenat64design}
shows the network setup.
When testing the NetPFGA/P4 performance, the X520 cards in the NAT64
translator are disconnected and instead the NetPFGA ports are
connected, as show in figure \ref{fig:netpfgadesign}. The load
generator is equipped with a quad core CPU (Intel(R) Core(TM) i7-6700
CPU @ 3.40GHz), enabled with hyperthreading and 16 GB RAM. The NAT64
translator is also equipped with a quard core CPU (Intel(R) Core(TM)
i7-4770 CPU @ 3.40GHz) and 16 GB RAM.
The first 10 seconds of the benchmark are excluded to avoid the TCP
warm up phase.\footnote{iperf -O 10 parameter, see section \ref{design:tests}.}
\begin{figure}[h]
  \includegraphics[scale=0.5]{netpfgadesign}
  \centering
  \caption{NAT64 with NetFPGA benchmark}
  \label{fig:netpfgadesign}
\end{figure}
% ok
% ----------------------------------------------------------------------


We successfully implemented P4 code to realise
NAT64~\cite{schottelius:thesisrepo}. It contains parsers
for all related protocols (ipv6, ipv4, udp, tcp, icmp, icmp6, ndp,
arp), supports EAMT as defined by RFC7757 ~\cite{rfc7757} and is
feature equivalent to the two compared software solutions
tayga~\cite{lutchansky:_tayga_simpl_nat64_linux} and
jool~\cite{mexico:_jool_open_sourc_siit_nat64_linux}.
Due to limitations in the P4 environment of the
NetFPGA~\cite{conclusion:netfpga} environment, the BMV2 implementation
is more feature rich. Table \ref{tab:benchmark} summarises the
achieved bandwidths of the NAT64 solutions.


\begin{table}[htbp]
\begin{center}\begin{minipage}{\textwidth}
\begin{tabular}{| c | c | c | c | c |}
\hline
Implementation & \multicolumn{4}{|c|}{min/avg/max in Gbit/s} \\
\hline
Tayga & 2.79 / 3.20 / 3.43 & 3.34 / 3.36 / 3.38 & 2.57 / 3.02 / 3.27 &
2.35 / 2.91 / 3.20 \\
\hline
Jool & 8.22 / 8.22 / 8.22  & 8.21 / 8.21 / 8.22  & 8.21 / 8.23 / 8.25
& 8.21 / 8.23 / 8.25\\
\hline
P4 / NetPFGA & 9.28 / 9.28 / 9.29 & 9.28 / 9.28 / 9.29  & 9.28 / 9.28
/ 9.29 & 9.28 / 9.28 / 9.29\\
\hline
Parallel connections & 1 & 10 & 20 & 50 \\
\hline
\end{tabular}
\end{minipage}
\caption{IPv6 to IPv4 TCP NAT64 Benchmark}
\label{tab:benchmarkv6}
\end{center}
\end{table}


During the benchmarks the client -- CPU usage
\begin{table}[htbp]
\begin{center}\begin{minipage}{\textwidth}
\begin{tabular}{| c | c | c | c | c |}
\hline
Implementation & \multicolumn{4}{|c|}{min/avg/max in Gbit/s} \\
\hline
Tayga & 2.90 / 3.15 / 3.34 & 2.87 / 3.01 / 3.22 &
2.68 / 2.85 / 3.09 & 2.60 / 2.78 / 2.88 \\
\hline
Jool & 7.18 / 7.56 / 8.24 & 7.97 / 8.05 / 8.09 &
8.05 / 8.08 / 8.10 & 8.10 / 8.12 / 8.13 \\
\hline
P4 / NetPFGA & 8.51 / 8.53 / 8.55 & 9.28 / 9.28 / 9.29 & 9.29 / 9.29 /
9.29 & 9.28 / 9.28 / 9.29 \\
\hline
Parallel connections & 1 & 10 & 20 & 50 \\
\hline
\end{tabular}
\end{minipage}
\caption{IPv4 to IPv6 TCP NAT64 Benchmark}
\label{tab:benchmarkv4}
\end{center}
\end{table}


\begin{table}[htbp]
\begin{center}\begin{minipage}{\textwidth}
\begin{tabular}{| c | c | c | c | c |}
\hline
Implementation & \multicolumn{4}{|c|}{avg bandwidth in gbit/s / avg loss /
  adjusted bandwith} \\
\hline
Tayga & 8.02 / 70\% / 2.43 & 9.39 / 79\% / 1.97 & 15.43 / 86\% / 2.11
& 19.27 / 91\% 1.73 \\
\hline
Jool & 6.44 / 0\% / 6.41 & 6.37 / 2\% / 6.25 &
16.13 / 64\% / 5.75 & 20.83 / 71\% / 6.04 \\
\hline
P4 / NetPFGA & 8.28 / 0\% / 8.28 & 9.26 / 0\% / 9.26 &
16.15 / 0\% / 16.15 & 15.8 / 0\% / 15.8 \\
\hline
Parallel connections & 1 & 10 & 20 & 50 \\
\hline
\end{tabular}
\end{minipage}
\caption{IPv6 to IPv4 UDP NAT64 Benchmark}
\label{tab:benchmarkv4}
\end{center}
\end{table}


\begin{table}[htbp]
\begin{center}\begin{minipage}{\textwidth}
\begin{tabular}{| c | c | c | c | c |}
\hline
Implementation & \multicolumn{4}{|c|}{avg bandwidth in gbit/s / avg loss /
  adjusted bandwith} \\
\hline
Tayga & 6.78 / 84\% / 1.06 & 9.58 / 90\% / 0.96 &
15.67 / 91\% / 1.41 & 20.77 / 95\% / 1.04 \\
\hline
Jool         & 4.53 / 0\% / 4.53 & 4.49 / 0\% / 4.49 & 13.26 / 0\% / 13.26 &
22.57 / 0\% / 22.57\\
\hline
P4 / NetPFGA & 7.04 / 0\% / 7.04 & 9.58 / 0\% / 9.58 &
9.78 / 0\% / 9.78 & 14.37 / 0\% / 14.37\\
\hline
Parallel connections & 1 & 10 & 20 & 50 \\
\hline
\end{tabular}
\end{minipage}
\caption{IPv4 to IPv6 UDP NAT64 Benchmark}
\label{tab:benchmarkv4}
\end{center}
\end{table}

UDP load generator hitting 100\% cpu at P20.
TCP confirmed.
Over bandwidth results

Feature comparison
speed - sessions - eamt
can act as host
lpm tables
ping
ping6 support
ndp
controller support

netpfga consistent