static_routes.tex

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% $XORP: xorp/docs/user_manual/static_routes.tex,v 1.15 2007/01/23 03:56:47 pavlin Exp $
%

\chapter{Static Routes}
\label{static_routes}
\section{Terminology and Concepts}

A static route is a manually configured route.  Static routes will not
automatically change if a link or neighboring router fails.  In
general, static routes should only be used for very simple network
topologies, or to override the behaviour of a dynamic routing protocol
for a small number of routes.

Static routes can be configured for IPv4 and IPv6.  Each route can be
specified as to be used for unicast forwarding, or as part of the
multicast topology used by multicast routing, or both.  

The term {\it RIB} refers to the router's {\it Routing Information
Base}.  This is the collection of all routes the router has learned
from its configuration or from its dynamic routing protocols.  The RIB
maintains separate collections of routes for IPv4 and IPv6.  Within
each of those collections, the router also maintains separate route
tables for unicast routes and for multicast routes.  Unicast routes
will be used to determine the forwarding table used for unicast packet
forwarding.  Multicast routes do not directly determine the multicast
forwarding table, but instead are used by multicast routing protocols
such as PIM.  PIM uses this to determine the RPF (Reverse-Path
Forwarding) information\footnote{The RPF information represents the path back
to a source.} needed to route 
multicast control information that in turn sets up the multicast
forwarding tree.  The part of the {\it RIB} used to contain multicast
topology information is called the {\it Multicast RIB} or {\it MRIB}.

\newpage
\section{Configuration of Static Routes}

When a static route is specified, it is necessary to indicate not only
the {\it destination subnet} and {\it next-hop} router, but also
whether the route should be placed in the unicast RIB or in the MRIB
or both.

\subsection{Configuration Syntax}

The syntax for defining static routes is shown below.

\vspace{0.1in}
\noindent\framebox[\textwidth][l]{\scriptsize
\begin{minipage}{6in}
\begin{alltt}
\begin{tabbing}
xx\=xx\=xx\=xx\=xx\=\kill
protocols \{\\
\>static \{\\
\>\>targetname: {\it text}\\
\>\>disable: {\it bool}\\
\>\>route {\it IPv4-addr}/{\it int(0..32)} \{\\
\>\>\>next-hop: {\it IPv4-addr}\\
\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>qualified-next-hop {\it IPv4-addr} \{\\
\>\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>\}\\
\>\>\}\\
\>\>route {\it IPv6-addr}/{\it int(0..128)} \{\\
\>\>\>next-hop: {\it IPv6-addr}\\
\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>qualified-next-hop {\it IPv6-addr} \{\\
\>\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>\}\\
\>\>\}\\
\\
\>\>mrib-route {\it IPv4-addr}/{\it int(0..32)} \{\\
\>\>\>next-hop: {\it IPv4-addr}\\
\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>qualified-next-hop {\it IPv4-addr} \{\\
\>\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>\}\\
\>\>\}\\
\>\>mrib-route {\it IPv6-addr}/{\it int(0..128)} \{\\
\>\>\>next-hop: {\it IPv6-addr}\\
\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>qualified-next-hop {\it IPv6-addr} \{\\
\>\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>\}\\
\>\>\}\\
\>\>interface-route {\it IPv4-addr}/{\it int(0..32)} \{\\
\>\>\>next-hop-interface: {\it text}\\
\>\>\>next-hop-vif: {\it text}\\
\>\>\>next-hop-router: {\it IPv4-addr}\\
\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>qualified-next-interface {\it text} \{\\
\>\>\>\>qualified-next-vif {\it text} \{\\
\>\>\>\>\>next-hop-router: {\it IPv4-addr}\\
\>\>\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\\
{\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
\\
\>\>interface-route {\it IPv6-addr}/{\it int(0..128)} \{\\
\>\>\>next-hop-interface: {\it text}\\
\>\>\>next-hop-vif: {\it text}\\
\>\>\>next-hop-router: {\it IPv6-addr}\\
\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>qualified-next-interface {\it text} \{\\
\>\>\>\>qualified-next-vif {\it text} \{\\
\>\>\>\>\>next-hop-router: {\it IPv6-addr}\\
\>\>\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\\
\>\>mrib-interface-route {\it IPv4-addr}/{\it int(0..32)} \{\\
\>\>\>next-hop-interface: {\it text}\\
\>\>\>next-hop-vif: {\it text}\\
\>\>\>next-hop-router: {\it IPv4-addr}\\
\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>qualified-next-interface {\it text} \{\\
\>\>\>\>qualified-next-vif {\it text} \{\\
\>\>\>\>\>next-hop-router: {\it IPv4-addr}\\
\>\>\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\>\>mrib-interface-route {\it IPv6-addr}/{\it int(0..128)} \{\\
\>\>\>next-hop-interface: {\it text}\\
\>\>\>next-hop-vif: {\it text}\\
\>\>\>next-hop-router: {\it IPv6-addr}\\
\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>qualified-next-interface {\it text} \{\\
\>\>\>\>qualified-next-vif {\it text} \{\\
\>\>\>\>\>next-hop-router: {\it IPv6-addr}\\
\>\>\>\>\>metric: {\it uint(1..65535)}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\>\}\\
\}
\end{tabbing}
\end{alltt}
\end{minipage}
}
\vspace{0.1in}

The configuration parameters are used as follows:
\begin{description}
\item{\tt protocols}: this delimits the configuration for all routing
  protocols in the XORP router configuration.  It is mandatory that
  BGP configuration is under the {\stt protocols} node in the
  configuration.
\item{\tt static}: the delimits the part of the router configuration
  that is related to configuring static routes.
\item{\tt targetname}: this is the name for this instance of
  static\_routes.  It defaults to ``{\stt static\_routes}'', and it is
  not recommended that this default is overridden under normal usage
  scenarios.
\item{\tt disable}: this takes the value {\stt true} or {\stt false},
  and determines whether any static routes are installed or not~\footnote{Note
  that prior to XORP Release-1.1, the {\tt enable} flag was used instead of
  {\tt disable}.}.
  Setting it to {\stt true} has the same effect as deleting the whole
  static routes configuration, but without losing what the old
  configuration actually was.
\item{\tt route}: this specifies an unicast route to be installed in the
  RIB~\footnote{Note that prior to the XORP Release-1.3, route4 and route6
  statements were used for IPv4 and IPv6 routes respectively.}.  The
  parameter is an IPv4 or IPv6 destination subnet expressed in the form
  {\it address/prefix-length}.

  Each {\stt route}: specification takes the following attributes:
\begin{description}
\item{\tt next-hop}: this specifies the IPv4 or IPv6 address (in case of
  IPv4 or IPv6 destination respectively) of the nexthop router towards
  the destination subnet~\footnote{Note that prior to the XORP
  Release-1.1, the {\tt nexthop} attribute was used instead of {\tt
  next-hop}.}. It is mandatory.
\item{\tt metric}: this specifies the routing metric or cost for this
  route.  It is a non-negative integer.  The metric for a static route
  is not directly used to decide which route to use, but may affect
  the choice of routes for protocols such as BGP and PIM-SM that
  indirectly use this information.  For example, BGP uses the IGP
  metric to the nexthop to decide between alternative routes as part
  of its decision process.  As with all routing metrics, lower values
  indicate better routes. The default is 1.
\item{\tt qualified-next-hop}: this specifies an alternative nexthop
  router for the route, but with a different metric. Typically it is
  used to install a backup static route that will be used in case the
  original next hop becomes unreachable.

  Each {\stt qualified-next-hop}: specification takes the following
  attributes:

\begin{description}
\item{\tt metric}: this specifies the routing metric or cost for this
  qualified route.  It is a non-negative integer.  Typically its value
  is larger than the metric for the primary next-hop.
  The default is 10.
\end{description}

\end{description}

\item{\tt mrib-route}: this specifies an multicast route to be installed
  in the Multicast RIB~\footnote{Note that prior to the XORP
  Release-1.3, mrib-route4 and mrib-route6 statements were used for IPv4
  and IPv6 routes respectively.}.  The parameter is an IPv4 or IPv6
  destination subnet expressed in the form {\it address/prefix-length}.
  This route will not directly affect forwarding, but will be used by
  multicast routing protocols such as PIM-SM to control how multicast
  trees are formed.

  An {\stt mrib-route} specification takes the same attributes as a
  {\stt route} specification.

\item{\tt interface-route}: this specifies an unicast route to be
  installed in the RIB~\footnote{Note that prior to the XORP
  Release-1.3, interface-route4 and interface-route6 statements were
  used for IPv4 and IPv6 routes respectively.}.  The parameter is an
  IPv4 or IPv6 destination subnet expressed in the form {\it
  address/prefix-length}. Typically, this specification will be used in
  wireless environment to install static routes where this router and
  next-hop router don't share the same subnet address on some (wireless)
  interface.

  Each {\stt interface-route}: specification takes the following attributes:

\begin{description}
\item{\tt next-hop-interface}: this specifies the name of the nexthop
  interface towards the destination subnet. It is mandatory.
\item{\tt next-hop-vif}: this specifies the name of the nexthop
  vif towards the destination subnet. It is mandatory.
\item{\tt next-hop-router}: this specifies the IPv4 or IPv6 address (in
  case of IPv4 or IPv6 destination respectively) of the nexthop router
  towards the destination subnet. The default is 0.0.0.0 or :: (for
  IPv4 and IPv6 respectively).
\item{\tt metric}: this specifies the routing metric or cost for this
  route.  See {\stt route metric} for details. The default is 1.
\item{\tt qualified-next-hop-interface}: this specifies an alternative
  nexthop interface for the route, but with a different
  metric. Typically it is used to install a backup static route that
  will be used in case the original next hop becomes unreachable.

  Each {\stt qualified-next-hop-interface}: specification takes the
  following attributes:

\begin{description}

\item{\tt qualified-next-hop-vif}: this specifies an alternative
  nexthop vif for the route, but with a different metric.

  Each {\stt qualified-next-hop-vif}: specification takes the following
  attributes:

\begin{description}
\item{\tt next-hop-router}: this specifies the IPv4 or IPv6 address (in
  case of IPv4 or IPv6 destination respectively) of the nexthop router
  towards the destination subnet.
\item{\tt metric}: this specifies the routing metric or cost for this
  qualified route.  It is a non-negative integer.  Typically its value
  is larger than the metric for the primary next-hop.
  The default is 10.
\end{description}

\end{description}

\end{description}

\end{description}

The {\tt mrib-interface-route} specification is same as the {\tt
interface-route} specification, except that it is used to configure
routes that are to be installed in the Multicast RIB.

\newpage
\subsection{Example Configurations}
\vspace{0.1in}
\noindent\framebox[\textwidth][l]{\scriptsize
\begin{minipage}{6in}
\begin{alltt}
\begin{tabbing}
xx\=xx\=xx\=xx\=xx\=\kill
protocols \{\\
\>static \{\\
\>\>route 10.20.0.0/16 \{\\
\>\>\>next-hop: 10.10.10.20\\
\>\>\>metric: 1\\
\>\>\>qualified-next-hop 172.17.0.2 \{\\
\>\>\>\>metric: 10\\
\>\>\>\}\\
\>\>\}\\
\>\>route 20:20:20:20::/64 \{\\
\>\>\>next-hop: 10:10:10:10:10:10:10:20\\
\>\>\>metric: 1\\
\>\>\}\\
\>\>\\
\>\>mrib-route 10.20.0.0/16 \{\\
\>\>\>next-hop: 10.10.10.30\\
\>\>\>metric: 1\\
\>\>\}\\
\>\>mrib-route 20:20:20:20::/64 \{\\
\>\>\>next-hop: 10:10:10:10:10:10:10:30\\
\>\>\>metric: 1\\
\>\>\}\\
\>\>\\
\>\>interface-route 10.30.0.0/16 \{\\
\>\>\>next-hop-interface: rl0\\
\>\>\>next-hop-vif: rl0\\
\>\>\>metric: 1\\
\>\>\>qualified-next-hop-interface rl1 \{\\
\>\>\>\>qualified-next-hop-vif rl1 \{\\
\>\>\>\>\>metric: 10\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\>\>interface-route 30:30:30:30::/64 \{\\
\>\>\>next-hop-interface: rl0\\
\>\>\>next-hop-vif: rl0\\
\>\>\>metric: 1\\
\>\>\}\\
\>\>\\
\>\>mrib-interface-route 10.30.0.0/16 \{\\
\>\>\>next-hop-interface: rl1\\
\>\>\>next-hop-vif: rl1\\
\>\>\>metric: 1\\
\>\>\}\\
\>\>mrib-interface-route 30:30:30:30::/64 \{\\
\>\>\>next-hop-interface: rl1\\
\>\>\>next-hop-vif: rl1\\
\>\>\>metric: 1\\
\>\>\}\\
\>\}\\
\}
\end{tabbing}
\end{alltt}
\end{minipage}
}
\vspace{0.1in}


\newpage
\section{Monitoring Static Routes}

IPv4 unicast static routes can be displayed using the command {\stt show route
table ipv4 unicast static}:

\vspace{0.1in}
\noindent\framebox[\textwidth][l]{\scriptsize
\begin{minipage}{6in}
\begin{alltt}
\begin{tabbing}
xxxxxxxxxxxxxxxx\=\kill
user@hostname> \textbf{show route table ipv4 unicast static}\\
192.168.0.0/24 \>[static(1)/1]\\
               \>> to 192.150.187.1 via fxp0/fxp0\\
192.168.1.0/24 \>[static(1)/1]\\
               \>> to 192.150.187.2 via fxp0/fxp0
\end{tabbing}
\end{alltt}
\end{minipage}
}

\vspace{0.1in} 
The information shown for each route not only indicates the configured
information (network, nexthop and metric), but also the interface
and vif via which this route will forward packets.

If the nexthop is not actually reachable, the route will not be shown
by this command because there is not current interface or vif.

\vspace{0.2in}
IPv6 unicast static routes can be displayed using the command {\stt show route
table ipv6 unicast static}.

The Multicast RIB static routes can be displayed using the commands
{\stt show route table ipv4 multicast static} and
{\stt show route table ipv6 multicast static} for IPv4 and IPv6 respectively.