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