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Add section regarding bgp sendholdtimer

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netravnen 2024-09-01 22:07:06 +02:00
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chapter/layer3.tex
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@ -369,3 +369,34 @@ Problems by running \textit{Full Mesh} is the formula of \[ iBGPsessions = n*(n-
\item distance is set to 20 compared to 200 for \gls{ibgp} routes,
\item Next hop does \textit{not} change for \gls{ebgp} routes advertised to \gls{ibgp} neighbours \textit{by-default}\footnote{Often times it is necessary to tell a router to set itself as the next-hop before advertising to \gls{ibgp} neighbours}.
\end{enumerate}
\subsection[bgpzombies]{Border Gateway Protocol Zombies}
\gls{bgp} zombies\cite{ietf-idr-bgp-sendholdtimer-00} can occuer for a multitude of reasons. Depending on the implementation. Examples are
\begin{enumerate}
\item Overloaded control plane
\item Unable to send out update/keepalives due to full out queues
\item Stuck TCP session the \gls{bgp} daemon is unaware of (e.g. tcp window size changed to 0)
\end{enumerate}
The consequence of \gls{bgp} sessions not being able to close properly. Can sometimes result in zombie routes. Where the router originating the route. Due to having one or more stuck sessions. Are unable to send out WITHDRAW messages. Thereby other routers think the route is still active. And does not withdraw the route from their own \gls{rib}. Ending up with a \gls{rib} containing STALL routes.
One workaround to get rid of zombie routes is to completely reset your routers \gls{rib}. This can be done by example rebooting network edge routers\cite{Navigati54:online}.
As of writing (Nov 2023) the following known public implementations have implemented the draft,
\begin{enumerate}
\item FRRouting\cite{bgpdimpl26:online}
\item neo-bgp\cite{Whatdoes40:online} (bgp.tools)
\item OpenBGPD\cite{Rebgpdse40:online}
\end{enumerate}
As of writing (Nov 2023) the following known public implementations are working on implementing the draft,
\begin{enumerate}
\item BIRD \url{https://gitlab.nic.cz/labs/bird/}\\
branch BGP_SendHoldTimer
\end{enumerate}
It is unknown when commercial vendors will implement the current internet draft. This will most likely not happen until the draft has been adopted as an official RFC.