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ospf topology

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netravnen 2018-02-18 14:35:06 +01:00
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@ -60,7 +60,7 @@ going on at around the same time.
\subsection{Algorithm} \subsection{Algorithm}
The protocol uses Dijkstra\tsq{s} algorithm when calculating metrics The protocol uses Dijkstra\tsq{s} algorithm when calculating metrics
mathematically.\cite{wiki:Dijkstra's_algorithm} mathematically.
The exchange of routing updates is done with \gls{ospf} own method. Directly The exchange of routing updates is done with \gls{ospf} own method. Directly
using IP protocol 89 and multicast address 224.0.0.5 for link-local updates and using IP protocol 89 and multicast address 224.0.0.5 for link-local updates and
@ -73,6 +73,32 @@ router to handle the exchange of routing information updates. And a backup
designated router is elected should the primary fail at some point. So as to designated router is elected should the primary fail at some point. So as to
avoid instability in the exchange of updates. avoid instability in the exchange of updates.
Dijkstra\tsq{s} algorithm. First formulated by computer scientist Edsger W.
Dijkstra in 1956 and published 1959. Is the formula behind \gls{ospf} path
calculation.\cite{wiki:Dijkstra's_algorithm}
Every node in the network knows about every path to any given destination in
the network. And only the best path is then selected for candidate route to be
used for forwarding traffic.
\subsubsection{Topology}
OSPF is divided into areas hierarchically. With the backbone area being the
authoritative central area.
\fig{ospf/area-hierarchy}{OSPF Area Hierarchy}{OSPF Area Hierarchy}
All traffic is forced to go by the backbone area when in transit from one area
to another. This in turn works fine for the most part. But requires strict
discipline when expanding and/or upgrading the network.
This is even more true when networks merge (fx. company merger/acquisition)
together. The ugly solution to having areas to far away from the backbone area
is Virtual links between ABRs across a non-backbone area.
\fig{ospf/virtual-link}{OSPF Virtual Link}{OSPF Virtual Link between abr
routers across non-backbone area}
\subsubsection{Database}
\subsection{Timers} \subsection{Timers}
\subsection{Filtering} \subsection{Filtering}

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