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124 lines
5.1 KiB
TeX
124 lines
5.1 KiB
TeX
\section{Spanning Tree}
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Spanning Tree exists for the \textbf{sole} reason to save "your" network and all the broadcast storms an network engineer having a bad day can by mistake create!
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STP comes from the above desire where redundancy was wanted but no protocol existed before STP to help in this regard.
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\begin{table}[h]
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\centering
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\caption{Spanning Tree standrds}
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\label{stpstandards}
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\resizebox{\columnwidth}{!}{%
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\begin{tabular}{|l|l|l|l|l|}
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\hline
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\textbf{} & \textbf{Standard} & \textbf{Ressource Usage} & \multicolumn{2}{l|}{\textbf{Convergence}} \\ \hline
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CST & 802.1D & Low & Slow & All vlans \\ \hline
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PVST+ & Cisco & High & Slow & Per vlan \\ \hline
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RSTP & 802.1w & So-so (Med.) & Fast & All vlans \\ \hline
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RPVST+ & Cisco & On-the-double (V.High) & Fast & Per vlan \\ \hline
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MST & 802.1s & Med. - High & Fast & Vlan list \\ \hline
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\end{tabular}%
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}
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\end{table}
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\subsection{Port Roles}
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When a switch is enabled for Spanning Tree. One of the following roles will have been assumed by any port on the switch in question.
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\begin{itemize}
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\item \textbf{Root port:} Only 1 port on any switch (non-counting the root bridge!). Is always the port with the lowest metric (aka. best path) to the root bridge.
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\item \textbf{Designated port:} A designated port is the port on any segment closest to the root bridge and forwarding traffic.
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\item \textbf{\textit{Non}-designated port:} Put in blocking mode and not currently forwarding traffic.
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\item \textbf{Disabled port:} The port has been one-way-or-another shut down.
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\end{itemize}
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\subsection{Standards}
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\begin{itemize}
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\item STP {\scriptsize Spanning Tree Protocol}
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\begin{itemize}
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\item Ieee 802.1D
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\item Was created in a time where bridged networks was the norm.
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\item Supports a single vlan/lan.
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\end{itemize}
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\item CST {\scriptsize Common Spanning Tree}
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\begin{itemize}
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\item An evolution of stp
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\item Cst still only supports one stp instance.
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\item But cst do thou in contrast to stp support \textit{multiple} vlans.
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\end{itemize}
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\item PVST {\scriptsize Per Vlan Spanning Tree}
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\begin{itemize}
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\item Now obsolute and succeded by pvst+
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\end{itemize}
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\item PVST+ {\scriptsize Per Vlan Spanning Tree Plus}
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\begin{itemize}
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\item Runs an instance of stp per vlan.
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\item Can guarante better utilization of available network bandwidth.
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\item Root bridge and port priorities can be configured per vlan.
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\end{itemize}
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\item RSTP {\scriptsize Rapid Spanning Tree Protocol}
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\begin{itemize}
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\item Ieee 802.1w
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\item A future development of the original 802.1D standard meant to provide faster convergance. As the original stp standard wasn't actually that fast.
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\end{itemize}
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\item RPVST+ {\scriptsize Rapid Per Vlan Spanning Tree Plus}
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\begin{itemize}
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\item A cisco implementation of rstp based upon pvst+.
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\end{itemize}
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\item MST {\scriptsize Multiple Spanning Tree}
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\begin{itemize}
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\item Originally a cisco developed protocol. Mst has since been developed as an ieee standard.
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\item Mst can as cst map multiple vlans to a single stp instance.
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\item Mst \textit{differently} than cst supports multiple stp instances.
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\item Fx. Instance 1: Vlan 1-99, Instane 2: Vlan 100-199.
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\end{itemize}
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\end{itemize}
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\subsection{Features}
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\subsubsection{BPDU}
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\textbf{B}ridge \textbf{P}rotocol \textbf{D}ata \textbf{U}nits is on cisco equipment sent out every 2 seconds and generally catogorizes into 2 categories:
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\begin{itemize}
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\item \textit{Configuration} bpdu used for stp calculations and
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\item \textit{Topology change notifications} bpdus used to notify other network nodes of a change in the network.
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\end{itemize}
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Any network node with switchports and stp + bpdu enabled sends out bpdu packets with the ports mac as the src address. The destination mac is is designated stp multicast addr 01:80:C2:00:00:00.
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\subsubsection{Root bridge}
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Using a \textbf{R}oot \textbf{B}rigde as the reference point for the stp instance and calculation of root/designated/non-designated ports.\\This election process uses a pre-configured bridge priority (ranges from $0$ to $2^{16}$) (defaults to $2^{15}$). If a tie in priority is found the switch in possession of the lowest mac address wins the root bridge election.
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\subsubsection{Port}
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\begin{itemize}
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\item PortFart
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\begin{itemize}
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\item
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\end{itemize}
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\item UplinkFast
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\begin{itemize}
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\item
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\end{itemize}
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\item BackboneFast
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\begin{itemize}
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\item
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\end{itemize}
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\end{itemize}
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\subsubsection{Loop prevention}
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\begin{itemize}
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\item BPDU Guard
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\item BPDU Filter
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\item Root Guard
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\item Loop Guard
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\end{itemize}
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\subsubsection{Link}
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\begin{itemize}
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\item Unidirectional Link Detection (UDLD)
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\item FlexLinks
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\end{itemize}
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