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Update section: BGP

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netravnen 2017-08-19 20:01:18 +02:00
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chapter/layer3.tex
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The protocol of the internet used since 1994.\cite{wiki:Border_Gateway_Protocol}
Currently based upon \rfc{4271} with updates following in \rfc{6286} \rfc{6608}, \rfc{6793}, \rfc{7606}, \rfc{7607}, \rfc{7705}.
\subsection{Properties}
\begin{itemize}
\item \itemhead{Properties}
\begin{itemize}
\item Uses tcp/179 as \gls{dst} port
\item Sends keep-alive message every 1 minute
\item Keep-alive message is 19 byte
\end{itemize}
\item \itemhead{Route exchange}
\begin{itemize}
\item \itemhead{Route-maps mechanism}
\begin{itemize}
\item Routes can be aggregated between \glspl{as}.
\item Properties can be changed on the fly by mathing
\begin{enumerate}[label={\alph*)}]
\item \Gls{bgp} communities,
\item \Gls{ip} prefix,
\item \Gls{bgp} as-path,
\end{enumerate}
\end{itemize}
\end{itemize}
\item \itemhead{States}
\begin{enumerate}
\item Idle: \gls{bgp} while initializing refuses all incoming connections. Will initiate \gls{tcp} connection to peer.
\item Connect: Waits for \gls{tcp} connection. If \gls{tcp} is established goes to state OpenSent. If \gls{tcp} is \textit{un}successful ConnectRetry timer is started and then goes to Active state.
\item Active: When ConnectRetry counter reaches 0 goes to state Connect.
\item OpenSent: Sends \gls{msg} to remote node. Waits for reply \gls{msg} before going to OpenConfirm.
\item OpenConfirm: Nodes exchange keepalive \glspl{msg} and goes to Established state if successful.
\item Established: Nodes can now exchange KeepAlive, Updates, and Notification \glspl{msg}.
\item Uses tcp/179 as \gls{dst} port
\item Sends keep-alive message every 1 minute
\item Keep-alive message is 19 byte long
\end{itemize}
Be ware if sessions are terminated immediately upon trying to establish connection. Try debugging following points.
\begin{itemize}
\item tcp/179 is not open,
\item random port 1023> is not open,
\item incorrect peer-ip,
\item incorrect peer-as.
\end{itemize}
\subsection{Route exchange}
Exchanging routes between routers is a reliant and tolerant manner is \glspl{bgp} 1-advantage over \gls{ospf}/\gls{isis}/\gls{rip}/\gls{eigrp}.
The sheer tuning and control mechanisms \gls{bgp} can offer is simply astounding. Route-maps is the key and access-lists just one option.
\subsubsection[Route-maps]{Route-maps mechanism}
Route-maps is used to target a select set of routes and either modify/add/remove attributes attached to the select route-set.
\begin{itemize}
\item Routes can be aggregated between \glspl{as}.
\item Properties can be changed on the fly by matching
\begin{enumerate}[label={\alph*)}]
\item \Gls{bgp} communities,
\item \Gls{ip} prefix,
\item \Gls{bgp} as-path,
\end{enumerate}
\end{itemize}
An simple example of using route-maps is
\begin{cisco}
ip prefix-list 1 permit 172.16.0.0/16
ip prefix-list 2 permit 192.168.1.0/24
!
route-map RED permit 10
match ip address prefix-list 1
set ip next hop 10.1.1.1
continue 20 ! Continues to apply rules normally only
! applied to prefix-list 2. To apply to
! prefix-list 1, too.
! Any attributes set in '20' will
! override any set during '10'.
route-map RED permit 20
match ip address prefix-list 2
set ip next hop 10.2.2.2 ! Last rule overrides previous rules from
! previous '10' rule-set.
\end{cisco}
When rules from a rule-set is chained together as shown above. The last rule will override all previous set values regarding the attribute being applied. In this case \texttt{next-hop} from 'permit 10' is overridden in 'permit 20'.
\subsection[States]{BGP States}
The states is the way \gls{bgp} handles peer/neighbor connection establishing. The \underline{playbook} so to speak.
\begin{enumerate}
\item Idle: \gls{bgp} while initializing refuses all incoming connections. Will initiate \gls{tcp} connection to peer.
\item Connect: Waits for \gls{tcp} connection. If \gls{tcp} is established goes to state OpenSent. If \gls{tcp} is \textit{un}successful ConnectRetry timer is started and then goes to Active state.
\item Active: When ConnectRetry counter reaches 0 goes to state Connect.
\item OpenSent: Sends \gls{msg} to remote node. Waits for reply \gls{msg} before going to OpenConfirm.
\item OpenConfirm: Nodes exchange keepalive \glspl{msg} and goes to Established state if successful.
\item Established: Nodes can now exchange KeepAlive, Updates, and Notification \glspl{msg}.
\end{enumerate}
\subsection[iBGP]{Internal Border Gateway Protocol}
\gls{ibgp} is running \gls{bgp} within the same \gls{as} between routers. Much like running a general \gls{igrp} in the network.