forwarding.tex

xorp源码hg

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% $XORP: xorp/docs/user_manual/forwarding.tex,v 1.12 2006/10/17 22:26:07 pavlin Exp $
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\chapter{Forwarding Engine}

\section{Terminology and Concepts}

The forwarding engine is that part of a router that receives packets
and forwards then from one interface to another.  In the case of XORP,
the forwarding engine may be the kernel forwarding path on UNIX,
the Click forwarding path~\cite{CLICK-PROJECT}, or it may reside in
external forwarding hardware.

On any particular router, it might be desirable to enable or disable
different parts of the forwarding functionality.  For example, a
router might only be intended to forward IPv6 packets but not IPv4
packets, or it might be intended to forward unicast packets but not
multicast packets.  Thus XORP provides the ability to enable and
configure various forwarding functionality.

In XORP, the term ``{\stt fea}'' refers to {\it Forwarding Engine
Abstraction} and the term ``{\stt mfea}'' refers to {\it Multicast
Forwarding Engine Abstraction}.  The term ``abstraction'' here refers to
a high-level configuration interface that should be the same
irrespective of whether the forwarding engine is provided in software
in the operating system kernel or in external forwarding hardware.

\newpage
\section{Configuration of the Forwarding Engine}

On a XORP router, forwarding functionality must be explicitly enabled
or no packets will be forwarded.  Forwarding can be separately enabled
for unicast and multicast, and for IPv4 and IPv6.  In addition,
multicast interfaces/vifs need to be explicitly enabled individually,
and certain special-purpose forwarding functionality can also be
enabled for multicast.

\subsection{Configuration Syntax}
\vspace{0.1in}
\noindent\framebox[\textwidth][l]{\scriptsize
\begin{minipage}{6in}
\begin{alltt}
\begin{tabbing}
xx\=xx\=xx\=xx\=xx\=\kill
fea \{\\
\>targetname: {\it txt}\\
\>unicast-forwarding4 \{\\
\>\>disable: {\it bool}\\
\>\>forwarding-entries \{\\
\>\>\>retain-on-startup: {\it bool}\\
\>\>\>retain-on-shutdown: {\it bool}\\
\>\>\}\\
\>\}\\
\>unicast-forwarding6 \{\\
\>\>disable: {\it bool}\\
\>\>forwarding-entries \{\\
\>\>\>retain-on-startup: {\it bool}\\
\>\>\>retain-on-shutdown: {\it bool}\\
\>\>\}\\
\>\}\\
\>click \{\\
\>\>disable: {\it bool}\\
\>\>duplicate-routes-to-kernel: {\it bool}\\
\\
\>\>kernel-click \{\\
\>\>\>disable: {\it bool}\\
\>\>\>install-on-startup: {\it bool}\\
\>\>\>kernel-click-modules: {\it text}\\
\>\>\>mount-directory: {\it text}\\
\>\>\>kernel-click-config-generator-file: {\it text}\\
\>\>\}\\
\\
\>\>user-click \{\\
\>\>\>disable: {\it bool}\\
\>\>\>command-file: {\it text}\\
\>\>\>command-extra-arguments: {\it text}\\
\>\>\>command-execute-on-startup: {\it bool}\\
\>\>\>control-address: {\it IPv4-addr}\\
\>\>\>control-socket-port: {\it uint(1..65535)}\\
\>\>\>startup-config-file: {\it text}\\
\>\>\>user-click-config-generator-file: {\it text}\\
\>\>\}\\
\>\}\\
\}
\\
{\rm continued overleaf....}
\end{tabbing}
\end{alltt}
\end{minipage}
}
\newpage
\vspace{0.1in}
\noindent\framebox[\textwidth][l]{\scriptsize
\begin{minipage}{6in}
\begin{alltt}
\begin{tabbing}
xx\=xx\=xx\=xx\=xx\=\kill
plumbing \{\\
\>mfea4 \{\\
\>\>disable: {\it bool}\\
\>\>interface {\it text} \{\\
\>\>\>vif {\it text} \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\}\\
\>\>\}\\
\>\>interface register\_vif \{\\
\>\>\>vif register\_vif \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\}\\
\>\>\}\\
\>\>traceoptions \{\\
\>\>\>flag all \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\}\\
\>\>\}\\
\>\}\\
\\
\>mfea6 \{\\
\>\>disable: {\it bool}\\
\>\>interface {\it text} \{\\
\>\>\>vif {\it text} \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\}\\
\>\>\}\\
\>\>interface register\_vif \{\\
\>\>\>vif register\_vif \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\}\\
\>\>\}\\
\>\>traceoptions \{\\
\>\>\>flag \{\\
\>\>\>\>all \{\\
\>\>\>\>\>disable: {\it bool}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\>\}\\
\}
\end{tabbing}
\end{alltt}
\end{minipage}
}
\vspace{0.1in}

\begin{description}
\item{\tt fea}: this delimits the configuration for the unicast
  forwarding engine functionality. 
  The following unicast forwarding engine parameters can be configured:
\begin{description}
\item{\tt targetname}: this is the name for this instance of the
  forwarding engine abstraction.  It defaults to ``{\stt fea}'', and
  it is strongly recommended that this default is {\it not} overridden
  under normal usage scenarios.
\end{description}

\item{\tt unicast-forwarding4}: this directive is used to configure the IPv4
  forwarding~\footnote{Note that prior to XORP Release-1.1, the
  {\tt enable-unicast-forwarding4} flag was used instead to enable or disable
  the IPv4 forwarding.}.
\begin{description}
\item{\tt disable}: this takes the value {\stt true} or {\stt false},
  and disables or enables all IPv4 unicast forwarding on the router.
  The default is {\stt false}.
\item{\tt forwarding-entries}: this directive is used to configure the
  properties of the IPv4 forwarding entries.
\begin{description}
\item{\tt retain-on-startup}: this takes the value {\stt true} or
  {\stt false}, and is used to control whether the XORP IPv4 unicast
  forwarding entries (if there are any left from a previous execution)
  are removed on startup by the FEA itself. The default is {\stt false}.
\item{\tt retain-on-shutdown}: this takes the value {\stt true} or
  {\stt false}, and is used to control whether the XORP IPv4 unicast
  forwarding entries are removed on shutdown by the FEA itself.
  The default is {\stt false}.
\end{description}
   Note that the {\tt retain-on-startup} and {\tt retain-on-shutdown}
   statements prevent the FEA itself from deleting the forwarding
   entries and does not prevent the RIB or any of the unicast routing
   protocols from deleting the entries on shutdown.
\end{description}

\item{\tt unicast-forwarding6}: this directive is used to configure the IPv6
  forwarding~\footnote{Note that prior to XORP Release-1.1, the
  {\tt enable-unicast-forwarding6} flag was used instead to enable or disable
  the IPv6 forwarding.}.
\begin{description}
\item{\tt disable}: this takes the value {\stt true} or {\stt false},
  and disables or enables all IPv6 unicast forwarding on the router.
  The default is {\stt false}.
\item{\tt forwarding-entries}: this directive is used to configure the
  properties of the IPv6 forwarding entries.
\begin{description}
\item{\tt retain-on-startup}: this takes the value {\stt true} or
  {\stt false}, and is used to control whether the XORP IPv6 unicast
  forwarding entries (if there are any left from a previous execution)
  are removed on startup by the FEA itself. The default is {\stt false}.
\item{\tt retain-on-shutdown}: this takes the value {\stt true} or
  {\stt false}, and is used to control whether the XORP IPv6 unicast
  forwarding entries are removed on shutdown by the FEA itself.
  The default is {\stt false}.
\end{description}
   Note that the {\tt retain-on-startup} and {\tt retain-on-shutdown}
   statements prevent the FEA itself from deleting the forwarding
   entries and does not prevent the RIB or any of the unicast routing
   protocols from deleting the entries on shutdown.
\end{description}

\item{\tt click}: this directive is used to configure the Click
  forwarding path.
\begin{description}
\item{\tt disable}: this takes the value {\stt true} or {\stt false},
  and disables or enables the Click forwarding path on the router. The
  default is {\stt false}.
\item{\tt duplicate-routes-to-kernel}: this takes the value {\stt true}
  or {\stt false}, and is used to control whether the XORP routes added
  to Click should be added to the system kernel as well. The default is
  {\stt false}.

\item{\tt kernel-click}: this directive is used to configure
  kernel-level Click.
\begin{description}
\item{\tt disable}: this takes the value {\stt true} or {\stt false},
  and disables or enables the kernel-level Click forwarding path on the
  router. The default is {\stt false}.
\item{\tt install-on-startup}: this takes the value {\stt true} or {\stt
  false}, and is used to specify whether the kernel-level Click should
  be installed on startup. The default is {\stt false}.
\item{\tt kernel-click-modules}: this specifies the list of Click
  modules (separated by ':') that should be loaded into the kernel.
  The default is the list of modules needed by Linux:
  ``/usr/local/click/linuxmodule/proclikefs.o:/usr/local/click/linuxmodule/click.o''
  For FreeBSD, the only module that is needed is ``click.ko'' so the
  list should be like: ``/path/to/click.ko''.
\item{\tt mount-directory}: this specifies the name of the directory to
  mount the Click file system on. The default is: ``/click''.
\item{\tt kernel-click-config-generator-file}: this specifies the name
  of the program to execute that would generate the kernel-level Click
  configuration from the XORP configuration. The default is:
  ``/usr/local/xorp/fea/xorp\_fea\_click\_config\_generator''.
\end{description}

\item{\tt user-click}: this directive is used to configure user-level
  Click.
\begin{description}
\item{\tt disable}: this takes the value {\stt true} or {\stt false},
  and disables or enables the user-level Click forwarding path on the
  router. The default is {\stt false}.
\item{\tt command-file}: this specifies the name of the user-level
  Click binary program to execute. The default is
  ``/usr/local/bin/click''.
\item{\tt command-extra-arguments}: this specifies the extra arguments
  that should be supplied to the user-level Click binary program when
  executing it. The default is ``-R''. Note that it should not contain
  ``\verb=-p <port>='', because it will be in conflict with the FEA's
  addition of the same argument.
\item{\tt command-execute-on-startup}: this takes the value {\stt true}
  or {\stt false}, and is used to specify whether the user-level Click
  binary program should be executed on startup. The default is {\stt
  false}.
\item{\tt control-address}: this takes an IPv4 address and is used to
  specify the address that the user-level Click binary program would be
  listening on for incoming connections (to control and reconfigure
  Click). The default is 127.0.0.1.
\item{\tt control-socket-port}: this takes an integer in the interval
  [1..65535] and is used to specify the TCP port number the user-level
  Click binary program would be listening on for incoming connections
  (to control and reconfigure Click). The default is 13000.
\item{\tt startup-config-file}: this specifies the name of the initial
  Click configuration file that would loaded on startup. The default is
  ``/dev/null''.
\item{\tt user-click-config-generator-file}: this specifies the name
  of the program to execute that would generate the user-level Click
  configuration from the XORP configuration. The default is
  ``/usr/local/xorp/fea/xorp\_fea\_click\_config\_generator''.