ospf.tex

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% $XORP: xorp/docs/user_manual/ospf.tex,v 1.12 2007/03/20 21:44:33 atanu Exp $
% 

\chapter{OSPFv2 and OSPFv3}
\label{ospf}
\section{OSPF Terminology and Concepts}

OSPF is the Open Shortest Path First protocol, it is one of two
principle Interior Gateway Protocols (IGP) the other being IS-IS. RIP
is also an IGP however OSPF and IS-IS have better scaling properties.

The initial OSPF specification is RFC 2328 OSPF Version 2 or
OSPFv2. This specification is specific to IPv4. There is a later
specification draft-ietf-ospf-ospfv3-update-14.txt OSPF for IPv6,
which happens to be Version 3 or OSPFv3.

The specifications for OSPFv2 and OSPFv3 are fairly similar the
obvious difference is the handing of IPv4 and IPv6 addresses.

The XORP implementation of OSPF supports both OSPFv2 and OSPFv3.

For consistency with our other protocols OSPFv2 is {\tt ospf4} and
OPSFv3 is {\tt ospf6} in the configuration files, the {\tt 4} in {\tt
ospf4} refers to the IPv4 address family and {\tt 6} in {\tt ospf6}
refers to the IPv6 address family.

\subsection{Key OSPF Concepts}

As an Interior Gateway Protocol OSPF runs within a single Autonomous
System. One way that OSPF achieves good scaling properties is to allow
an AS to be split into distinct regions that OSPF calls areas. The areas
are structured in a two level hierarchy, area {\tt 0.0.0.0} is special
and is called the {\tt BACKBONE} area. All other areas must be
connected to that {\tt BACKBONE} either directly or through virtual links.

A fundamental quantity in OSPF that describes topology and routing
information is the Link State Advertisement (LSA). Every OSPF router
within an area should have exactly the same LSAs in its
database. There are different type of LSAs the base specification
describes Router-LSAs, Network-LSAs, Summary-LSAs and AS-external-LSAs.

The OSPF protocol has explicit support for introducing routes from
other protocols, these routes are introduced via AS-external-LSAs. For
example, routes from a RIP cloud can be introduced into OSPF and will
appear as AS-external-LSAs.

Areas in OSPF can be one of three different types {\tt normal}, {\tt
stub} and {\tt Not-So-Stubby}. The {\tt BACKBONE} is always {\tt
normal}. All LSAs in OSPF are flooded only within an area, the
exception is the AS-external-LSA that can be flooded between all {\tt
normal} areas.

OSPF routers are categorised into four overlapping categories, an
internal router whose interfaces are all in one area, an area border
router ({\tt ABR}) that has interfaces in more than one area, a backbone router
that has an interface to the {\tt BACKBONE} and an AS boundary router
that introduces routes from other protocols.

An AS boundary router can be configured in {\tt normal} and {\tt
Not-So-Stubby} areas. In a {\tt normal} area the AS boundary router
generates an AS-external-LSA that is flooded to all other {\tt normal}
areas. In a {\tt Not-So-Stubby} an AS boundary router generates a
Type-7 LSA that {\bf may} be translated at a area border router to an
AS-external-LSA, which will be flooded to all {\tt normal} areas. An
AS-external-LSA is never flooded into a {\tt stub} or {\tt
Not-So-Stubby} area. The different types of areas exist to limit the
number of LSAs in a particular area, for example a {\tt stub} area may
have a small number of internal routes and default routes to the
{\tt ABR}s.

\section{Standards}

XORP OSPF complies with the following standards:
\begin{description}
\item{\bf RFC 2328}: OSPF Version 2
\item{\bf draft-ietf-ospf-ospfv3-update-14.txt} OSPF for IPv6
\item{\bf RFC 3101}: The OSPF Not-So-Stubby Area (NSSA) Option
\end{description}

\newpage
\section{Configuring OSPF}

\subsection{Configuration Syntax}

The configuration syntax for XORP OSPFv2 is given below.

\vspace{0.1in}
\noindent\framebox[\textwidth][l]{\scriptsize
\begin{minipage}{6in}
\begin{alltt}
\begin{tabbing}
xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=\kill
protocols \{\\
\>ospf4 \{\\
\>\>targetname: {\it text}\\
\>\>router-id: {\it IPv4}\\
\>\>rfc1583-compatibility: {\it bool};
\>\>ip-router-alert: {\it bool}\\
\\
\>\>traceoptions \{\\
\>\>\>flag \{\\
\>\>\>\>all \{\\
\>\>\>\>\>disable: {\it bool}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\\
\>\>area {\it IPv4} \{\\
\>\>\>area-type: {\it text}\\
\\
\>\>\>default-lsa \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\>metric: {\it uint(0..0xffffff)}\\
\>\>\>\}\\
\\
\>\>\>summaries \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\}\\
\\
\>\>\>area-range {\it IPv4Net} \{\\
\>\>\>\>advertise: {\it bool}\\
\>\>\>\}\\
\\
\>\>\>virtual-link {\it IPv4} \{\\
\>\>\>\>transit-area: {\it ipv4}\\
\>\>\>\>hello-interval: {\it uint(1..65535)}\\
\>\>\>\>router-dead-interval: {\it uint(1..65535)}\\
\>\>\>\>retransmit-interval: {\it uint(1..65535)}\\
\>\>\>\>transit-delay: {\it uint(0..3600)}\\
\>\>\>\>authentication \{\\
\>\>\>\>\>simple-password: {\it text}\\
\\
\>\>\>\>\>md5 {\it uint(0..255)} \{\\
\>\>\>\>\>\>password: {\it text}\\
\>\>\>\>\>\>start-time: {\it text(``YYYY-MM-DD.HH:MM'')}\\
\>\>\>\>\>\>end-time: {\it text(``YYYY-MM-DD.HH:MM'')}\\
\>\>\>\>\>\>max-time-drift: {\it uint(0..65535)}\\
\>\>\>\>\>\}\\
\>\>\>\>\}\\
\>\>\>\}\\
\\
{\rm continued overleaf....}
\end{tabbing}
\end{alltt}
\end{minipage}
}
\vspace{0.1in}

\newpage
\vspace{0.1in}
\noindent\framebox[\textwidth][l]{\scriptsize
\begin{minipage}{6in}
\begin{alltt}
\begin{tabbing}
xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=\kill
\>\>\>interface {\it text} \{\\
\>\>\>\>link-type: {\it text}\\
\\
\>\>\>\>vif {\it text} \{\\
\\
\>\>\>\>\>address {\it IPv4} \{\\
\>\>\>\>\>\>priority: {\it uint(0..255)}\\
\>\>\>\>\>\>hello-interval: {\it uint(1..65535)}\\
\>\>\>\>\>\>router-dead-interval: {\it uint(1..4294967295)}\\
\>\>\>\>\>\>interface-cost: {\it uint(1..65535)}\\
\>\>\>\>\>\>retransmit-interval: {\it uint(1..65535)}\\
\>\>\>\>\>\>transit-delay: {\it uint(0..3600)}\\
\>\>\>\>\>\>authentication \{\\
\>\>\>\>\>\>\>simple-password: {\it text}\\
\\
\>\>\>\>\>\>\>md5 {\it uint(0..255)} \{\\
\>\>\>\>\>\>\>\>password: {\it text}\\
\>\>\>\>\>\>\>\>start-time: {\it text(``YYYY-MM-DD.HH:MM'')}\\
\>\>\>\>\>\>\>\>end-time: {\it text(``YYYY-MM-DD.HH:MM'')}\\
\>\>\>\>\>\>\>\>max-time-drift: {\it uint(0..65535)}\\
\>\>\>\>\>\>\>\}\\
\>\>\>\>\>\>\}\\
\>\>\>\>\>\>passive: {\it text}\\
\\
\>\>\>\>\>\>neighbor  {\it IPv4}\{\\
\>\>\>\>\>\>\>router-id: {\it IPv4}\\
\>\>\>\>\>\>\}\\
\\
\>\>\>\>\>\>disable: {\it bool}\\
\>\>\>\>\>\}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\\
\>\>import: {\it text} \\
\>\>export: {\it text}\\
\>\}\\
\}
\end{tabbing}
\end{alltt}
\end{minipage}
}
\vspace{0.1in}

\newpage
The configuration syntax for XORP OSPFv3 is given below.

\vspace{0.1in}
\noindent\framebox[\textwidth][l]{\scriptsize
\begin{minipage}{6in}
\begin{alltt}
\begin{tabbing}
xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=\kill
protocols \{\\
\>ospf6 \{\\
\>\>targetname: {\it text}\\
\>\>router-id: {\it IPv4}\\
\>\>ip-router-alert: {\it bool}\\
\\
\>\>traceoptions \{\\
\>\>\>flag \{\\
\>\>\>\>all \{\\
\>\>\>\>\>disable: {\it bool}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\\
\>\>area {\it IPv4} \{\\
\>\>\>area-type: {\it text}\\
\\
\>\>\>default-lsa \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\>metric: {\it uint(0..0xffffff)}\\
\>\>\>\}\\
\\
\>\>\>summaries \{\\
\>\>\>\>disable: {\it bool}\\
\>\>\>\}\\
\>\>\>area-range {\it IPv6Net} \{\\
\>\>\>\>advertise: {\it bool}\\
\>\>\>\}\\
\>\>\>virtual-link {\it IPv4} \{\\
\>\>\>\>transit-area: {\it ipv4}\\
\>\>\>\>hello-interval: {\it uint(1..65535)}\\
\>\>\>\>router-dead-interval: {\it uint(1..65535)}\\
\>\>\>\>retransmit-interval: {\it uint(1..65535)}\\
\>\>\>\>transit-delay: {\it uint(0..3600)}\\
\>\>\>\}\\
\\
%{\rm continued overleaf....}
%\end{tabbing}
%\end{alltt}
%\end{minipage}
%}
%\vspace{0.1in}

%\newpage
%\vspace{0.1in}
%\noindent\framebox[\textwidth][l]{\scriptsize
%\begin{minipage}{6in}
%\begin{alltt}
%\begin{tabbing}
%xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=xx\=\kill
\>\>\>interface {\it text} \{\\
\>\>\>\>link-type: {\it text}\\
\\
\>\>\>\>vif {\it text} \{\\
\\
\>\>\>\>\>address {\it IPv6} \{\\
\>\>\>\>\>\>disable: {\it bool}\\
\>\>\>\>\>\}\\
\>\>\>\>\>priority: {\it uint(0..255)}\\
\>\>\>\>\>hello-interval: {\it uint(1..65535)}\\
\>\>\>\>\>router-dead-interval: {\it uint(1..4294967295)}\\
\>\>\>\>\>interface-cost: {\it uint(1..65535)}\\
\>\>\>\>\>retransmit-interval: {\it uint(1..65535)}\\
\>\>\>\>\>transit-delay: {\it uint(0..3600)}\\
\>\>\>\>\>passive: {\it text}\\
\>\>\>\>\>neighbor  {\it IPv4}\{\\
\>\>\>\>\>\>router-id: {\it IPv4}\\
\>\>\>\>\>\}\\
\>\>\>\>\>disable: {\it bool}\\
\>\>\>\>\>\}\\
\>\>\>\>\}\\
\>\>\>\}\\
\>\>\}\\
\\
\>\>import: {\it text} \\
\>\>export: {\it text}\\
\>\}\\
\}
\end{tabbing}
\end{alltt}
\end{minipage}
}
\vspace{0.1in}

\noindent
The OSPFv2 and OSPFv3 configurations are practically equivalent with
the following exceptions:
\begin{itemize}
\item OSPFv3 does not support authentication in the protocol itself.
\item OSPFv2 supports a single address per interface/vif, therefore all
parameters are set below the address node.
\item OSPFv3 supports multiple addresses per interface/vif, therefore
parameters are set below the vif node.
\item OSPFv3 does not require any addresses to be configured in which
case it will advertise all global addresses configured on the
interface/vif. If any addresses are configured in OSPFv3 then only
those addresses will be advertised. If it is required that no
addresses should be advertised then configuring an address and
disabling it, will stop any global addresses being advertised.
\item OSPFv3 in release 1.4 requires that a link local address is
configured on any interface/vif on which it is configured to run.
\end{itemize}

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
  OSPF configuration is under the {\stt protocols} node in the
  configuration.
\item{\tt ospf4}: This delimits the OSPFv2 configuration part of the XORP
  router configuration.
\item{\tt ospf6}: This delimits the OSPFv3 configuration part of the XORP
  router configuration.
\item{\tt targetname}: This is the name for this instance of OSPF.  It
  defaults to ``{\stt ospfv2}'', and it is not recommended that this
  default is overridden under normal usage scenarios.
\item{\tt router-id}: This is a unique IPv4 address within the
Autonomous System. The smallest IP address of an interface belonging
to the router is a good choice. The required format of the {\stt
router-id} is a dotted-decimal IPv4 address.
\item{\tt ip-router-alert}: This takes the value {\stt true} or {\stt
false}. The default state is {\stt false}, if set to {\stt true} the
IP router alert option will be placed in all transmitted packets.
\item{\tt traceoptions}: This directive if present will enable all tracing.
\item{\tt area}: This delimits an area in which multiple virtual links
and interfaces can be configured. The {\stt area} directive take an
area identifier parameter, which by convention is specified as a
dotted-decimal IPv4 address.
\begin{description}

\item{\tt area-type}: This is the type of the area, {\stt normal},
{\stt stub} or {\stt nssa}.

\item{\tt default-lsa}: This directive if present is affective for
{\stt stub} or {\stt nssa} areas only. If the router is an Area Border
Router, then a default-lsa will be introduced into this area.
\begin{description}
\item{\tt metric}: This is the metric in the default-lsa.
\item{\tt disable}: This takes the value {\stt true} or {\stt
false}. The default setting is {\stt false} it can be set to {\stt
true} to disable the sending of the default-lsa.
\end{description}
\end{description}
\begin{description}

\item{\tt summaries}: This directive if present is affective for
{\stt stub} or {\stt nssa} areas only. If the router is an Area Border
Router, then this option controls the introduction of Summary-LSAs into
the area.
\begin{description}
\item{\tt disable}: This takes the value {\stt true} or {\stt
false}. The default setting is {\stt false} it can be set to {\stt
true} to disable the sending of Summary-LSAs.
\end{description}
\end{description}

\begin{description}
\item{\tt area-range}: If the router is an Area Border Router the IPv4
network defines how to summarize this area into other areas.
\begin{description}
\item{\tt advertise}: This takes the value {\stt true} or {\stt
false}. The default setting is {\stt true} it can be set to {\stt
false} to disable the sending of Summary-LSAs. 
\end{description}
\end{description}

\begin{description}
\item{\tt virtual-link}: This is the {\stt router-id} of the router
with which a virtual link should be formed. Virtual links can only be
configured in the {\stt BACKBONE} area. The format of the parameter is
a dotted-decimal IPv4 address.
\begin{description}
\item{\tt transit-area}: This is the transit area through which the
virtual link is formed.
\item{\tt hello-interval}: This is the time in seconds between sending
hello packets.
\item{\tt router-dead-interval}: This is the time in seconds to wait before