cnp3-ebook/protocols/lan — French @ Weblate: 200

	English	French	Actions
	the `cost` of the shortest path between the switch that sent the `BPDU` and the root switch (`c`)
	the `identifier` of the switch that sent the `BPDU` (`T`)
	the number of the switch port over which the `BPDU` was sent (`p`)
	In addition to the `identifier` discussed above, the network administrator can also configure a `cost` to be associated to each switch port. Usually, the `cost` of a port depends on its bandwidth and the [IEEE802.1d]_ standard recommends the values below. Of course, the network administrator may choose other values. We will use the notation `cost[p]` to indicate the cost associated to port `p` in this section.
	Bandwidth
	Cost
	10 Mbps
	2000000
	100 Mbps
	200000
	1 Gbps
	20000
	2000
	100 Gbps
	200
	The `Spanning Tree Protocol` uses its own terminology that we illustrate in the figure above. A switch port can be in three different states : `Root`, `Designated` and `Blocked`. All the ports of the `root` switch are in the `Designated` state. The state of the ports on the other switches is determined based on the `BPDU` received on each port.
	The `Spanning Tree Protocol` uses the ordering relationship to build the spanning tree. Each switch listens to `BPDUs` on its ports. When `BPDU = <R,c,T,p>` is received on port `q`, the switch computes the port's `root priority vector`: `V[q] = <R,c+cost[q],T,p,q>` , where `cost[q]` is the cost associated to the port over which the `BPDU` was received. The switch stores in a table the last `root priority vector` received on each port. The switch then compares its own `identifier` with the smallest `root identifier` stored in this table. If its own `identifier` is smaller, then the switch is the root of the spanning tree and is, by definition, at a distance `0` of the root. The `BPDU` of the switch is then `<R,0,R,p>`, where `R` is the switch `identifier` and `p` will be set to the port number over which the `BPDU` is sent.
	Otherwise, the switch chooses the best priority vector from its table, `bv = <R,c+cost[q'],T,p,q'>`. The port `q'`, over which this best root priority vector was learned, is the switch port that is closest to the `root` switch. This port becomes the `Root` port of the switch. There is only one `Root` port per switch (except for the `Root` switches whose ports are all `Designated`). The switch can then compute its own `BPDU` as `BPDU = <R,c',S,p>` , where `R` is the `root identifier`, `c'` the cost of the best root priority vector, `S` the identifier of the switch and `p` will be replaced by the number of the port over which the `BPDU` will be sent.
	To determine the state of its other ports, the switch compares its own `BPDU` with the last `BPDU` received on each port. Note that the comparison is done by using the `BPDUs` and not the `root priority vectors`. If the switch's `BPDU` is better than the last `BPDU` of this port, the port becomes a `Designated` port. Otherwise, the port becomes a `Blocked` port.
	The state of each port is important when considering the transmission of `BPDUs`. The root switch regularly sends its own `BPDU` over all of its (`Designated`) ports. This `BPDU` is received on the `Root` port of all the switches that are directly connected to the `root switch`. Each of these switches computes its own `BPDU` and sends this `BPDU` over all its `Designated` ports. These `BPDUs` are then received on the `Root` port of downstream switches, which then compute their own `BPDU`, etc. When the network topology is stable, switches send their own `BPDU` on all their `Designated` ports, once they receive a `BPDU` on their `Root` port. No `BPDU` is sent on a `Blocked` port. Switches listen for `BPDUs` on their `Blocked` and `Designated` ports, but no `BPDU` should be received over these ports when the topology is stable. The utilization of the ports for both `BPDUs` and data frames is summarized in the table below.
	Port state
	Receives BPDUs
	Sends BPDU
	Handles data frames
	Blocked
	yes
	no
	Root
	Designated
	To illustrate the operation of the `Spanning Tree Protocol`, let us consider the simple network topology in the figure below.

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../../protocols/ethernet.rst:359

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2 years ago

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Translation file

locale/fr/LC_MESSAGES/protocols/lan.po, string 104